Question: latency.  To collect ACK delays on all the paths, hosts should rely on time stamps as described in QUIC-Timestamp. <ins> 7.1.4. ECN feedback in QUIC is provided based on counters in the ACK frame (see Section 19.3.2. of QUIC-TRANSPORT).  That means if an ACK frame acknowledges multiple packets, the ECN feedback cannot be accounted to a specific packet. There are separate counters for each packet number space.  However, sending to zero-length CID receivers, the same number space is used for multiple paths.  Respectively, if an ACK frames acknowledges multiple packets from different paths, the ECN feedback cannot unambiguously be assigned to a path. If the sender marks its packets with the ECN capable flags, the network will expect standard reactions to ECN marks, such as slowing down transmission on the sending path.  If zero-length CID is used, the sending path is however ambiguous.  Therefore, the sender MUST treat a CE marking as a congestion signal on all sending paths that have been by a packet that was acknowledged in the ACK frame signaling the CE counter increase. A host that is sending over multiple paths to a zero-length CID receiver MAY disable ECN marking and send all subsequent packets as Not-ECN capable. 7.1.5. Hosts that are designed to support multipath using multiple number spaces MAY adopt a conservative posture after negotiating multipath support with a peer using zero-length CID.  The simplest posture is to only send data on one path at a time, while accepting packets on all acceptable paths.  In that case: the attribution of packets to path discussed in zero-length-cid- loss-and-congestion are easy to solve because packets are sent on a single path, the ACK Delays are correct, the vast majority of ECN marks relate to the current sending path. Of course, the hosts will only take limited advantage from the multipath capability in these scenarios.  Support for "make before break" migrations will improve, but load sharing between multiple paths will not work. </ins> 7.2. <del> If the multipath option is enabled with a value of 2, each path has its own packet number space for transmitting 1-RTT packets and a new ACK frame format is used as specified in ack-mp-frame.  Compared to the QUIC version 1 ACK frame, the ACK_MP frames additionally contains a Packet Number Space Identifier (PN Space ID).  The PN Space ID used to distinguish packet number spaces for different paths and is simply </del> <ins> If packets contain a non-zero CID, each path has its own packet number space for transmitting 1-RTT packets and a new ACK frame format is used as specified in ack-mp-frame.  Compared to the QUIC version 1 ACK frame, the ACK_MP frames additionally contains a Packet Number Space Identifier (PN Space ID).  The PN Space ID used to distinguish packet number spaces for different paths and is simply </ins> derived from the sequence number of Destination Connection ID. Therefore, the packet number space for 1-RTT packets can be identified based on the Destination Connection ID in each packets.

Thanks for the summary NAME I think one point is missing in your list which is related to issue . Use of a single packet number space might not support ECN. Regarding the unified solution: I think what you actually say is that we would specify both solutions and everybody would need to implement both logics. At least regarding the "simplicity of code" argument, that would be the worst choice. If we can make the multiple packet number spaces solution work with one-sided CIDs, I'm tending toward such an approach. Use of multiple packet number spaces avoids ambiguity/needed "smartness" in ACK handling and packet scheduling which, as you say above, can make the implementation more complex and, moreover, wrong decisions may have large impact on efficient (both local processing and on-the-wire). I don't think we want to leave these things to each implementation individually.
The summary Christian made above about design comparison sounds indeed quite accurate. Besides ECN, my other concern about single packet number is that it require cleverness from the receiver side if you want to be performant in some scenarios. At the sender-side, you need to consider a path-relative packet number threshold instead of an absolute one to avoid spurious losses. Just a point I think we did not mentioned yet is that there can be some interactions between Multipath out-of-order number delivery and incoming packet number duplicate detection. This requires maintaining some state at the receiver side, as described by URL With single packet number space, the receiver should take extra care when updating the "minimum packet number below which all packets are immediately dropped". Otherwise, in presence of paths with very different latencies, the receiver might end up discarding packets from a (slower) path. I'm also preferring the multiple packet number spaces solution for the above reasons. I'm not against thinking for a "unified" solution (the proposal sounds interesting), but I wonder how much complexity this would add compared to requiring end hosts to use one-byte CIDs.
I think the issue is not really so much "single vs multiple number space" as "support for multipath and NULL CID". As noted by Mirja, there is an implementation cost there. My take is: If a node uses NULL CID and proposes support of multipath, then that node MUST implement code to deal with size of acknowledgements.


Question: latency.  To collect ACK delays on all the paths, hosts should rely on time stamps as described in QUIC-Timestamp. <ins> 7.1.4. ECN feedback in QUIC is provided based on counters in the ACK frame (see Section 19.3.2. of QUIC-TRANSPORT).  That means if an ACK frame acknowledges multiple packets, the ECN feedback cannot be accounted to a specific packet. There are separate counters for each packet number space.  However, sending to zero-length CID receivers, the same number space is used for multiple paths.  Respectively, if an ACK frames acknowledges multiple packets from different paths, the ECN feedback cannot unambiguously be assigned to a path. If the sender marks its packets with the ECN capable flags, the network will expect standard reactions to ECN marks, such as slowing down transmission on the sending path.  If zero-length CID is used, the sending path is however ambiguous.  Therefore, the sender MUST treat a CE marking as a congestion signal on all sending paths that have been by a packet that was acknowledged in the ACK frame signaling the CE counter increase. A host that is sending over multiple paths to a zero-length CID receiver MAY disable ECN marking and send all subsequent packets as Not-ECN capable. 7.1.5. Hosts that are designed to support multipath using multiple number spaces MAY adopt a conservative posture after negotiating multipath support with a peer using zero-length CID.  The simplest posture is to only send data on one path at a time, while accepting packets on all acceptable paths.  In that case: the attribution of packets to path discussed in zero-length-cid- loss-and-congestion are easy to solve because packets are sent on a single path, the ACK Delays are correct, the vast majority of ECN marks relate to the current sending path. Of course, the hosts will only take limited advantage from the multipath capability in these scenarios.  Support for "make before break" migrations will improve, but load sharing between multiple paths will not work. </ins> 7.2. <del> If the multipath option is enabled with a value of 2, each path has its own packet number space for transmitting 1-RTT packets and a new ACK frame format is used as specified in ack-mp-frame.  Compared to the QUIC version 1 ACK frame, the ACK_MP frames additionally contains a Packet Number Space Identifier (PN Space ID).  The PN Space ID used to distinguish packet number spaces for different paths and is simply </del> <ins> If packets contain a non-zero CID, each path has its own packet number space for transmitting 1-RTT packets and a new ACK frame format is used as specified in ack-mp-frame.  Compared to the QUIC version 1 ACK frame, the ACK_MP frames additionally contains a Packet Number Space Identifier (PN Space ID).  The PN Space ID used to distinguish packet number spaces for different paths and is simply </ins> derived from the sequence number of Destination Connection ID. Therefore, the packet number space for 1-RTT packets can be identified based on the Destination Connection ID in each packets.

If a node sees a peer using NULL CID and supporting multipath, then that node MUST either use only one path at a time or implement code to deal with impact on loss detection due to out of order arrivals, and impact on congestion control including ambiguity of ECN signals. Then add sections on what it means to deal with the side of acknowledgements, out of order arrivals, and congestion control. I think this approach ends up with the correct compromises: It keeps the main case simple. Nodes that rely on multipath just use long CID and one number space per CID. Nodes that use long CID never have to implement the ACK length minimization algorithms. Nodes that see a peer using NULL CID have a variety of implementation choices, e.g., sending on just one path at a time, sending on mostly one path at a time in "make or break" transitions, or implementing sophisticated algorithms. If we do that, we can get rid of the single vs multiple space discussion, and end up with a single solution addressing all use cases.
Looking at all the discussions here and in other issues such as ECN, I think that we should try to write two different versions of section 7: one covering all the aspects of single packet number space (RTT estimation, retransmissions, ECN, handling of CIDs, ...) one covering all the aspects of multiple packet number space (RTT estimation, retransmissions, ECN, handling of CIDs, ...) There would be some overlap between these two sections and also some differences that would become clear as we specify them. At the end of this writing, we'll know whether it is possible to support/unify both or we need to recommend a single one. The other parts of the document are almost independent of that and can evolve in parallel with these two sections. However, I don't think that such a change would be possible by Monday
I don't think we should rush changes before we have agreed on the final vision.
It might be helpful to have these options as PRs (without merging) them, so people can understand all details of each approach.
I agree with NAME that supporting multi-path with null CIDs is a more fundamental issue than the efficiency comparison between single PN and separate PN, as it would ultimately impact the application scope of multipath QUIC. But indeed, we might want to implement proposed solution first and then decide if we want to adopt such a unified approach.


Question: latency.  To collect ACK delays on all the paths, hosts should rely on time stamps as described in QUIC-Timestamp. <ins> 7.1.4. ECN feedback in QUIC is provided based on counters in the ACK frame (see Section 19.3.2. of QUIC-TRANSPORT).  That means if an ACK frame acknowledges multiple packets, the ECN feedback cannot be accounted to a specific packet. There are separate counters for each packet number space.  However, sending to zero-length CID receivers, the same number space is used for multiple paths.  Respectively, if an ACK frames acknowledges multiple packets from different paths, the ECN feedback cannot unambiguously be assigned to a path. If the sender marks its packets with the ECN capable flags, the network will expect standard reactions to ECN marks, such as slowing down transmission on the sending path.  If zero-length CID is used, the sending path is however ambiguous.  Therefore, the sender MUST treat a CE marking as a congestion signal on all sending paths that have been by a packet that was acknowledged in the ACK frame signaling the CE counter increase. A host that is sending over multiple paths to a zero-length CID receiver MAY disable ECN marking and send all subsequent packets as Not-ECN capable. 7.1.5. Hosts that are designed to support multipath using multiple number spaces MAY adopt a conservative posture after negotiating multipath support with a peer using zero-length CID.  The simplest posture is to only send data on one path at a time, while accepting packets on all acceptable paths.  In that case: the attribution of packets to path discussed in zero-length-cid- loss-and-congestion are easy to solve because packets are sent on a single path, the ACK Delays are correct, the vast majority of ECN marks relate to the current sending path. Of course, the hosts will only take limited advantage from the multipath capability in these scenarios.  Support for "make before break" migrations will improve, but load sharing between multiple paths will not work. </ins> 7.2. <del> If the multipath option is enabled with a value of 2, each path has its own packet number space for transmitting 1-RTT packets and a new ACK frame format is used as specified in ack-mp-frame.  Compared to the QUIC version 1 ACK frame, the ACK_MP frames additionally contains a Packet Number Space Identifier (PN Space ID).  The PN Space ID used to distinguish packet number spaces for different paths and is simply </del> <ins> If packets contain a non-zero CID, each path has its own packet number space for transmitting 1-RTT packets and a new ACK frame format is used as specified in ack-mp-frame.  Compared to the QUIC version 1 ACK frame, the ACK_MP frames additionally contains a Packet Number Space Identifier (PN Space ID).  The PN Space ID used to distinguish packet number spaces for different paths and is simply </ins> derived from the sequence number of Destination Connection ID. Therefore, the packet number space for 1-RTT packets can be identified based on the Destination Connection ID in each packets.

Since NAME prodded me, we now have a PR for the "unified" proposal.
I totally agree with Christian that the issue is about "support for multipath and NULL CID", and the solution that Christian suggested looks really great! It both takes advantage of multiple spaces, and support NULL CID users without affect the efficiency of ACK arrangements. Besides, the solution is more convenient for implementations, because If both endpoints uses non-zero length cids, endpoints only need to support multiple spaces, and if one of the endpoints use NULL CID, it could use single pn space in one direction and could support NULL CID and multipath at the same time.
Very high level summary of IETF-113 discussion seems that there is interest and likely support for the unified solution (review minutes for further details).


Question: Given these inputs, the derivation of secrets for an epoch proceeds as shown in the following diagram: <del> A number of secrets are derived from the epoch secret for different </del> <ins> A number of values are derived from the epoch secret for different </ins> purposes: <del> The "external secret" is used to derive an HPKE key pair whose </del> <ins> (In general, we use "secret" to refer to a value that is used derive further secret values, and "key" to refer to a value that is used with an algorithm such as HMAC or an AEAD algorithm.) The "external_secret" is used to derive an HPKE key pair whose </ins> private key is held by the entire group: The public key "external_pub" can be published as part of the

Looks good! I would maybe add 1 sentence explaining the rule for what is called a secret and what is called a key. The rule says that a secret will go through some key derivation to obtain a key/keys, is that right?
NAME Yep, that's exactly right. Added a sentence. Thanks for the feedback everyone!
Reopening due to incomplete discussion and inaccuracy. The claims presented are incorrect in response by NAME demonstrate a misunderstanding of the roles of these keys and uses, and constitutes a change to the fundamental uses thereof. The authenticationsecret is NOT a public value nor was it ever introduced as such. If an application is using it as a public value, that onus is on the developers, and I advise against using Cisco's implementation as a standard for MLS. As shown in the name and all original discussion, the authenticationsecret is intended as a secret value (or else 'public' in the same way that the group secret is 'public). It is used for further derivation to support authentication. This should be corrected, and such foundational changes without WG discussion should be avoided.
Clearly we have a disagreement here NAME but maybe let's hold off on attributing misunderstanding. It seems like you are claiming that in order for MLS to be secure, the needs to be protected to the same level as the . What is this based on? If that is true, then we should probably remove the altogether. The "out-of-band" protocol in which it would be confirmed would have to be part of the MLS security analysis, thus no longer out-of-band.
NAME that is not the claim at all - different uses imply different compromise risks. This should not be a new concept to understand. As demonstrated in the terminology, the authenticationsecret is linked to authentication, not confidentiality. MLS, per specification, outsources authentication (the AS is not explicitly defined and all entity authentication within MLS relies on it). Even though it is definitionally out-of-scope and therefore out-of-band (certificates, authentication verification are entirely out-of-band of the protocol spec), we do not say that signature secret keys can be "public" - yet you are asserting that an authenticationsecret which can support epoch-level authentication would be public.


Question: Given these inputs, the derivation of secrets for an epoch proceeds as shown in the following diagram: <del> A number of secrets are derived from the epoch secret for different </del> <ins> A number of values are derived from the epoch secret for different </ins> purposes: <del> The "external secret" is used to derive an HPKE key pair whose </del> <ins> (In general, we use "secret" to refer to a value that is used derive further secret values, and "key" to refer to a value that is used with an algorithm such as HMAC or an AEAD algorithm.) The "external_secret" is used to derive an HPKE key pair whose </ins> private key is held by the entire group: The public key "external_pub" can be published as part of the

The authenticationsecret is private in the same way that the exportervalue is: based on key schedule derivation, compromise of these keys should not undermine MLS, but secrecy of them can be leveraged. So, unless you are now proposing removing mention of certificates, etc. from the core protocol, there really isn't a logical basis for removing 'out-of-band' authentication mechanisms.
What I'm trying to get at here is: What is the negative consequence if an is known by someone other than the members of a group? For example, leaking a signature private key would enable the attacker to impersonate the corresponding member. Leaking the would allow the attacker to decrypt all of the group's messages. What is the bad consequence of an becoming public?
NAME I am also assuming that this push to use epoch-level authentication values as public codes is based on Cisco's implementation choice. I would be curious to know why there is such insistence that all implementations also go about using authentication in the same way. If an implementation chooses to use it as a secret value to then derive an authentication code based on yet other information, why is that a problem?
Publishing the authenticationsecret as a public value has a similar effect as publishing the exportervalue as public - it is not an issue for MLS per protocol spec, but it would definitely be an issue for the application if it is then used for something secret thereafter. One reason not to specify these as public values is that they are derived following the conditions placed on keys and therefore could be used as secret values if desired by an application. Forcing or annotating them as immediately public, or as final 'codes', when such a use as a secret key is an out-of-scope potential is artificial and unnecessary.
I'm not pushing anything, I'm just trying to get the protocol to be clear. If this thing needs to be secret, then it needs to be secret, and we need to document that so that people keep it secret. Thanks for elaborating more on your concerns. I see what you're saying -- basically the same point that NAME and I discussed . I think the core of the disagreement here is what we mean when we say that a value is "public" or "secret".


Question: Given these inputs, the derivation of secrets for an epoch proceeds as shown in the following diagram: <del> A number of secrets are derived from the epoch secret for different </del> <ins> A number of values are derived from the epoch secret for different </ins> purposes: <del> The "external secret" is used to derive an HPKE key pair whose </del> <ins> (In general, we use "secret" to refer to a value that is used derive further secret values, and "key" to refer to a value that is used with an algorithm such as HMAC or an AEAD algorithm.) The "external_secret" is used to derive an HPKE key pair whose </ins> private key is held by the entire group: The public key "external_pub" can be published as part of the

I mean something very specific: That the security guarantees of MLS will not be harmed if a public value is provided to the attacker, and they will be harmed if a secret value is provided to the attacker. Importantly, "public" does not mean that the value must be published, or that the security guarantees of an application using MLS will not be harmed if you publish the value. It seems to me that in that specific taxonomy, the is "public" and not "secret". Do you disagree?
BTW, the notion of something being "public" at one layer but "secret" at another is not new. For example, values exported from TLS aren't secret in the sense that publishing them would compromise TLS. You could authenticate your TLS connection by exporting a value and shouting it through megaphones across a crowd. But the main way people use them in practice is as secrets in some other protocol. Every WebRTC call uses SRTP keys that are exported from TLS, and many people would be very sad if these "public" values were published.
If it would help, I would be happy to add some text to the Security Considerations clarifying this distinction. Basically, draw a clear boundary around which values have to be kept confidential to the client in order to realize the security properties of the protocol. But I still think is a clearer name. Doesn't mean you have to use it in any particular way in your application; doesn't prevent it being used as a shared secret; but also doesn't imply that the MLS library has to worry about its secrecy.
Within the bounds of that particular taxonomy there is not an issue. However, while you may be following a given taxonomy, that is not a general one, one that would be widely understood by implementors, nor is it specified in the protocol spec. It is not an unreasonable taxonomy, but it certainly not a general one. If you are looking for MLS usage spec to align to your taxonomy then I do think that there should be a clarification section added. BTW as a point case on more standard terminology use, the TLS 1.3 spec uses the exact phrasing for exporters as "exportermastersecret", from which the actual exporter may be derived. This aligns very closely to the authenticationsecret, from which an authentication code later may be derived.


Question: Given these inputs, the derivation of secrets for an epoch proceeds as shown in the following diagram: <del> A number of secrets are derived from the epoch secret for different </del> <ins> A number of values are derived from the epoch secret for different </ins> purposes: <del> The "external secret" is used to derive an HPKE key pair whose </del> <ins> (In general, we use "secret" to refer to a value that is used derive further secret values, and "key" to refer to a value that is used with an algorithm such as HMAC or an AEAD algorithm.) The "external_secret" is used to derive an HPKE key pair whose </ins> private key is held by the entire group: The public key "external_pub" can be published as part of the

TLS is generic in 'exporters' after an exportermastersecret is derived. Thus there is alignment of the term 'secret' to things that can be used for keys (have sufficient entropy), not as an alignment to public/secret at different layers. I am strongly opposed to the use of authenticationcode, and see no clear definition for that in your customized taxonomy. As such, it would follow the more standard interpretations, such as message authentication codes, etc. which are indeed explicitly public values. Codes are normally an end-state in themselves, not keys. Perhaps it is a clearer name for the Cisco implementation design, but it is not a clear name for something that can/should be used for further derivations as may be more generally applicable. Following the TLS norm for exporters, the name would be "authenticationmastersecret". The shortened "authenticationsecret" was a good name. If you are going to provide a write-up for the custom taxonomy, then an adjustment to "authenticationexporter" could perhaps be made.
The notion of a having boundary to the protocol and values that may or may not safely be exported across the boundary is not exotic or customized. You see it in FIPS 140-2, PKCS, and WebCrypto, and in tools like ProVerif and Tamarin. The only choice I'm making is in the specific words, in particular reserving "secret" for "something that should not be exposed outside the protocol implementation because it would compromise the protocol". I hope you agree that is different from say in this regard. It would be OK for an MLS implementation to have an API for an application to access the , but it would not be OK to have an API to access the . I'm not wedded to , I just want something other than . If you want to align with the exported values (to which I agree it is similar), we could call it an .
The distinction between those documents and tools, and the MLS spec is that those tools clearly define the boundaries and terminology, vs. just anyone making terminology assumptions without them being specified in the document. Not to be pedantic, but if you want to assume specific meanings for terms relative to a threat model for MLS only, versus a general usage ("exporter secrets" being secrets used in other things), then you really do need to specify those assumptions within the specification itself and not various side discussions.


Question: Given these inputs, the derivation of secrets for an epoch proceeds as shown in the following diagram: <del> A number of secrets are derived from the epoch secret for different </del> <ins> A number of values are derived from the epoch secret for different </ins> purposes: <del> The "external secret" is used to derive an HPKE key pair whose </del> <ins> (In general, we use "secret" to refer to a value that is used derive further secret values, and "key" to refer to a value that is used with an algorithm such as HMAC or an AEAD algorithm.) The "external_secret" is used to derive an HPKE key pair whose </ins> private key is held by the entire group: The public key "external_pub" can be published as part of the

Such specification is part of what a standard is meant to do. Within other documents this is clearly defined - i.e., what is known as a threat model - such as one sees in ProVerif and Tamarin. Assuming that you are going to add such a taxonomy, and that it follows that described by you in , then the correct term would be "authenticationkey". To quote you what you said there, which correctly aligns to a reasonable usage of the authenticationkey. pointed out that there is a lack of consistency in the usage of "keys" vs "secrets" throughout the document - something that still has not been addressed and should not be dropped from the issue for edits. Regardless of what taxonomy is being used or even assumed, there is no consistency in it in the spec. You seem to be commenting on adjustments only for the "key" and "secret" uses that appear as variables, but the commentary within the spec interchangeably use these terms for the same thing. Whatever is used should be applied consistently. It is not reasonable to assume that developers will correctly guess reasons for terminology separations particularly when they are inconsistently enforced.
On your latter point about usage of "keys" vs "secrets" throughout the document — Sorry if I misinterpreted your intent here. If you're seeing places where there are inconsistencies, it would be helpful if you could highlight those more specifically, or ideally send a PR to fix them.
NAME had a call about this today and hashed out a couple of things: We should be clear in general about what we mean by secrets/keys, in that we generally use them interchangeably, but sometimes use one or the other to indicate how a specific value is used The need for secrecy of the value labeled depends on the context in which it is used. So we should provide some text to suggest that there are different ways to use it, and use a fairly neutral name. NAME suggested , which I like a lot. I have attempted to implement these in
The spec currently uses a mix of terminologies for keys/secrets.


Question: Given these inputs, the derivation of secrets for an epoch proceeds as shown in the following diagram: <del> A number of secrets are derived from the epoch secret for different </del> <ins> A number of values are derived from the epoch secret for different </ins> purposes: <del> The "external secret" is used to derive an HPKE key pair whose </del> <ins> (In general, we use "secret" to refer to a value that is used derive further secret values, and "key" to refer to a value that is used with an algorithm such as HMAC or an AEAD algorithm.) The "external_secret" is used to derive an HPKE key pair whose </ins> private key is held by the entire group: The public key "external_pub" can be published as part of the

In the key schedule we have the following: senderdatasecret | "sender data" encryptionsecret | "encryption" exportersecret | "exporter" authenticationsecret | "authentication" externalsecret | "external" confirmationkey | "confirm" membershipkey | "membership" resumptionsecret | "resumption" It would be best to provide a coherency to how we use these terms and check for consistency throughout, to avoid confusion for readers: A simple solution would be to use "secret" for all cases, i.e., changing membershipkey to membershipsecret.Another alternative, which may take more refining but could be useful to readers is to separate out terms based on items that are for internal protocol use versus external protocol use. For example, encryption, confirmation, membership, etc., would use "key" and exporter, authentication, etc., could use "secret", or vice versa. --Break-- Ref the mailinglist on confirmation vs authentication secrets, perhaps the naming of these two are a little misleading - authentication normally being within bounds of a protocol while confirmation is external to it. This confusion probably sparked some of that discussion to begin with. It could_ be worth considering switching those terms for clarity.
I actually think we have a fairly coherent taxonomy here: "secret" is something that gets fed into HKDF to derive further things "key" is something that gets fed into another algorithm, e.g., HMAC Looking through the list, the ones that deviate from this pattern are: , which is exported to the application but expected to be kept private , which is exported to the application but not expected to be kept private Given that, I would propose we update the table in question to something like the following, using because that's how it's used, and to follow the "security code" terminology used by applications:
Things are easier to understand like this! The "Purpose" column is quite valuable I think, I remember I was quite overwhelmed when I first read it and had no idea what all those secret / keys were used for. This helps to understand the big picture.


Question: The "signature" field in an MLSPlaintext object is computed using the signing private key corresponding to the public key, which was authenticated by the credential at the leaf of the tree indicated by <del> the sender field.  The signature covers the plaintext metadata and message content, which is all of MLSPlaintext except for the "signature", the "confirmation_tag" and "membership_tag" fields.  If the sender is a member of the group, the signature also covers the GroupContext for the current epoch, so that signatures are specific to a given group and epoch. </del> <ins> the sender field.  The signature is computed using "SignWithLabel" with label ""MLSPlaintextTBS"" and with a content that covers the plaintext metadata and message content, which is all of MLSPlaintext except for the "signature", the "confirmation_tag" and "membership_tag" fields.  If the sender is a member of the group, the content also covers the GroupContext for the current epoch, so that signatures are specific to a given group and epoch. </ins> The "membership_tag" field in the MLSPlaintext object authenticates the sender's membership in the group.  For an MLSPlaintext with a

Signatures as specified in the MLS protocol document are ambiguous, in the sense that signatures produced for one purpose in the protocol can be (maliciously) used in a different place of the protocol. Indeed, we found that for example, a can have the same serialization as , which proves that one signature could be accepted for different structures. The collisions we have found so far are quite artificial, so it is not super clear how to exploit this, but at least it makes it impossible to have provable security. The solution is pretty simple, we simply prefix each signed value with a label, in a fashion similar to . That way, when calling you can give the structure name in the argument.
Something that is still bothering me is the structure: struct { select (URL) { case member: GroupContext context; case preconfigured: case newmember: struct{}; } WireFormat wireformat; opaque groupid; uint64 epoch; Sender sender; opaque authenticateddata; ContentType contenttype; select (MLSPlaintextTBS.contenttype) { case application: opaque applicationdata; case proposal: Proposal proposal; case commit: Commit commit; } } MLSPlaintextTBS; Since the first is done on a field defined after it, this structure is not parsable. We could say that's not a problem since we only need to serialize it, but for security purposes I would recommend to put it at the end, like this: struct { WireFormat wireformat; opaque groupid; uint64 epoch; Sender sender; opaque authenticateddata; ContentType contenttype; select (MLSPlaintextTBS.contenttype) { case application: opaque applicationdata; case proposal: Proposal proposal; case commit: Commit commit; } select (URL) { case member: GroupContext context; case preconfigured: case newmember: struct{}; } } MLSPlaintextTBS; What do you think about it?
Nice one! Crafting collisions is probably not straightforward, but eliminating the the risk altogether is the way to go.
It is actually quite easy to craft collisions, I made a script do find them: URL (I wanted to check whether there was accidentally a way do disambiguate the structures)
Introduced in .


Question: The "signature" field in an MLSPlaintext object is computed using the signing private key corresponding to the public key, which was authenticated by the credential at the leaf of the tree indicated by <del> the sender field.  The signature covers the plaintext metadata and message content, which is all of MLSPlaintext except for the "signature", the "confirmation_tag" and "membership_tag" fields.  If the sender is a member of the group, the signature also covers the GroupContext for the current epoch, so that signatures are specific to a given group and epoch. </del> <ins> the sender field.  The signature is computed using "SignWithLabel" with label ""MLSPlaintextTBS"" and with a content that covers the plaintext metadata and message content, which is all of MLSPlaintext except for the "signature", the "confirmation_tag" and "membership_tag" fields.  If the sender is a member of the group, the content also covers the GroupContext for the current epoch, so that signatures are specific to a given group and epoch. </ins> The "membership_tag" field in the MLSPlaintext object authenticates the sender's membership in the group.  For an MLSPlaintext with a

s currently have two usages in the spec: Pre-published key packages that you can download and put in a leaf when adding a new member leaf node content that you update when doing a full Currently, things have been designed to use only one structure for both uses, leading to some weirdness such as: and are useful in the usage 1, but are parameters of the group in usage 2. is a good name in usage 1, but would better be named in usage 2. some data is important in usage 2 and have no meaning in usage 1, hence they were designed as "mandatory-when-updating extensions" (such as , and we were also discussing about adding the in to help prevent cross-group attacks) How about using different structures for these? // Essentially identical to KeyPackage struct { ProtocolVersion version; CipherSuite ciphersuite; HPKEPublicKey hpkeinitkey; opaque endpointid; Credential credential; Extension extensions; opaque signature; } PrePublishedKeyPackage; struct { HPKEPublicKey hpkekey; opaque endpointid; Credential credential; opaque parenthash; opaque groupid; Extension extensions; opaque signature; } LeafNodeContent; enum { reserved(0), prepublishedkeypackage(1), leafnodecontent(2), (255) } LeafNodeType; struct LeafNode { // This is not included in the signature, but with the "unambiguous signature" PR that's not a problem LeafNodeType type; select(URL) { case prepublishedkeypackage: PrePublishedKeyPackage data; case leafnode_content: LeafNodeContent data; } } What would you think about refactoring like this?
If we're doing this, I'd suggest including a dedicated public key to encrypt Welcome messages to for the . NAME suggested this at some point. It gives us better FS guarantees, because the receiver of the can delete the corresponding private key immediately after decryption, while they might have to keep the other key around for a bit until they can actually issue an update. This might also help clarify .
Ties into as well because is an example of an extension that is required and should be a field instead
NAME one concern I have is how is that field in created?
When sending a full , the participant includes a new in the (it replaces the field).


Question: The "signature" field in an MLSPlaintext object is computed using the signing private key corresponding to the public key, which was authenticated by the credential at the leaf of the tree indicated by <del> the sender field.  The signature covers the plaintext metadata and message content, which is all of MLSPlaintext except for the "signature", the "confirmation_tag" and "membership_tag" fields.  If the sender is a member of the group, the signature also covers the GroupContext for the current epoch, so that signatures are specific to a given group and epoch. </del> <ins> the sender field.  The signature is computed using "SignWithLabel" with label ""MLSPlaintextTBS"" and with a content that covers the plaintext metadata and message content, which is all of MLSPlaintext except for the "signature", the "confirmation_tag" and "membership_tag" fields.  If the sender is a member of the group, the content also covers the GroupContext for the current epoch, so that signatures are specific to a given group and epoch. </ins> The "membership_tag" field in the MLSPlaintext object authenticates the sender's membership in the group.  For an MLSPlaintext with a

It computes the signature with where: corresponds to all the fields of except (the usual thing) comes from
What about the scenario where Alice pulls down Bob's key package to add him to the group? In that case Alice can't do the conversion between formats on Bob's behalf.
Alice don't have to do the conversion, this is why either contain a (when adding someone to the group) or a (when updating your own key package).
Ah somehow I missed that part in your original post. Makes sense
I like this general direction. It solves a few things. Instead of having leaf nodes contain either a prepublished thing or a normal leaf node, how about having the prepublished thing wrap the leaf node thing? As a bonus, we get separation between the key pair used for Welcome encryption and the key pair that goes in the leaf for TreeKEM. Then when Alice adds Bob, she extracts his LeafNodeContent and sends that in the Add. That doesn't let the other members of the group verify that Alice did the right thing w.r.t. expiry, but I'm not heartbroken about that. We might also be able to remove the extensions field from the outer (KeyPackage) wrapping if we turn the extension into KeyPackage field. I expect we probably need leaf extensions, but would be open to making into a field.
Why not keep sending the KeyPackage in the Add? That wouldn't cost much and would allow everyone to validate the lifetime. Note, that the lifetime is crucial in achieving PCS for pre-published key material. If I compromise Bob and get hold of the private key material of a bunch of his KeyPackages, I can add "Bob" to any group I want as long as the Credential inside the LeafNodeContent remains valid and Bob doesn't revoke the LeafNodeContent somehow. Also, we'll have to do this if we want to enable any member to send the Welcome message as you proposed here: URL
I agree that including inside is quite clean, but something is bothering me with this approach: I'd like that the is signed by the participant occupying that leaf, to protect against cross-group attacks. In the first message of this issue I did this by including in , but in fact we don't need to store it in the leaf, we just need to include it in the .


Question: The "signature" field in an MLSPlaintext object is computed using the signing private key corresponding to the public key, which was authenticated by the credential at the leaf of the tree indicated by <del> the sender field.  The signature covers the plaintext metadata and message content, which is all of MLSPlaintext except for the "signature", the "confirmation_tag" and "membership_tag" fields.  If the sender is a member of the group, the signature also covers the GroupContext for the current epoch, so that signatures are specific to a given group and epoch. </del> <ins> the sender field.  The signature is computed using "SignWithLabel" with label ""MLSPlaintextTBS"" and with a content that covers the plaintext metadata and message content, which is all of MLSPlaintext except for the "signature", the "confirmation_tag" and "membership_tag" fields.  If the sender is a member of the group, the content also covers the GroupContext for the current epoch, so that signatures are specific to a given group and epoch. </ins> The "membership_tag" field in the MLSPlaintext object authenticates the sender's membership in the group.  For an MLSPlaintext with a

In any case, if we want to include in the signature, we need a way to differentiate between leaves that triggered a commit and the ones that are "fresh". And for that I think using a tagged-union struct is the cleanest way to do it.
It always feels a bit lazy to use an extension (and implementations have to be careful to check for their presence), but we could use a extension in the same way that we use a extension. You will find both of them only on LeafContents that were updated at least once. Another result of including GroupId in the KeyPackage is that the signature will explicitly sign the and I'm not sure if that doesn't completely destroy any deniability guarantees we can still get from MLS.
I don't think there's really a good way to get the into the leaf. Because of prepublication, it would have to be optional, but in order to prevent attacks, you need rules to decide whether it's required in a given situation. It seems like the best you can do is basically TOFU: When you first get the tree, you can't validate whether the groupid should be in a given leaf or not Once you're a member, you require that groupid is sent in Update and UpdatePath.leafkey_package I could live with a solution of that character, but given it's a bit complex, might prefer to leave it out unless we get a useful property from it. NAME - Re: Sending KeyPackage in Add - Yep, that makes sense. So you would send KeyPackage in Add, and LeafNode in Update.
I tried to worked through what would be necessary to implement this. It looks like it would require some fairly invasive changes to be made to rationalize the document's structure before making this change. But those changes should probably be made anyway.


Question: The "signature" field in an MLSPlaintext object is computed using the signing private key corresponding to the public key, which was authenticated by the credential at the leaf of the tree indicated by <del> the sender field.  The signature covers the plaintext metadata and message content, which is all of MLSPlaintext except for the "signature", the "confirmation_tag" and "membership_tag" fields.  If the sender is a member of the group, the signature also covers the GroupContext for the current epoch, so that signatures are specific to a given group and epoch. </del> <ins> the sender field.  The signature is computed using "SignWithLabel" with label ""MLSPlaintextTBS"" and with a content that covers the plaintext metadata and message content, which is all of MLSPlaintext except for the "signature", the "confirmation_tag" and "membership_tag" fields.  If the sender is a member of the group, the content also covers the GroupContext for the current epoch, so that signatures are specific to a given group and epoch. </ins> The "membership_tag" field in the MLSPlaintext object authenticates the sender's membership in the group.  For an MLSPlaintext with a

Proposal: Preparatory PR: Rationalize layout Move "Cryptograhic Objects" to before "Ratchet Trees" Update "Ratchet Tree Nodes" to define ParentNode and LeafNode structs, with LeafNode initially just equal to KeyPackage Move subsections of "Key Packages" to under "Ratchet Trees" Parent Hash Tree Hashes Update Paths Move Group State to its own top-level section Main PR: Change LeafNode to have the required content: HPKE key for TreeKEM Credential Parent hash Capabilities Extensions Signature Change KeyPackage to refer to LeafNode for internals, plus: HPKE key for Welcome Lifetime Extensions Signature Add continues to send KeyPackage Update and Commit send LeafNode instead of KeyPackage Remove and Sender refer to LeafNodeRef instead of KeyPackageRef We should probably do the preparatory PR regardless of this issue.
Discussion on working call: General agreement on the approach Should sign group_id when possible Include in TBS if we at least have a flag for pre-published / in-group Or we can store it Or we could have independent structs for pre-published / in-group leaves Do we need extensions at both levels? Capabilities / lifetime should probably be promoted to fields
From what I can see, there is no reason not to sign the context in the case of an external init. I'm not sure why it got taken out, but while implementing external inits, verification went through even when including the context.
As I commented in , it's not even clear that we need this context any more for members any more, given for MLSPlaintext and the AEAD of MLSCiphertext. So I would propose we just remove the context added to MLSPlaintextTBS altogether. NAME IIRC you were the one that proposed adding the context. WDYT?
This was fixed in
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Question: The "signature" field in an MLSPlaintext object is computed using the signing private key corresponding to the public key, which was authenticated by the credential at the leaf of the tree indicated by <del> the sender field.  The signature covers the plaintext metadata and message content, which is all of MLSPlaintext except for the "signature", the "confirmation_tag" and "membership_tag" fields.  If the sender is a member of the group, the signature also covers the GroupContext for the current epoch, so that signatures are specific to a given group and epoch. </del> <ins> the sender field.  The signature is computed using "SignWithLabel" with label ""MLSPlaintextTBS"" and with a content that covers the plaintext metadata and message content, which is all of MLSPlaintext except for the "signature", the "confirmation_tag" and "membership_tag" fields.  If the sender is a member of the group, the content also covers the GroupContext for the current epoch, so that signatures are specific to a given group and epoch. </ins> The "membership_tag" field in the MLSPlaintext object authenticates the sender's membership in the group.  For an MLSPlaintext with a

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Question: encapsulations for consistency but there is no hard requirement in this regard. <ins> Implementation details of PREOF functions is out of scope for this document.  IEEE802.1CB-2017 specifies replication and elimination specific aspects, which can be applied to PRF and PEF. </ins> 4.2.2.1. The Packet Replication Function (PRF) function MAY be supported by an

Proposed changes: 0, fixing Roman Danyliw comment 1, change introduction to highlight additional functions of data plane and the focus of the draft 2, highlight that implementation of PREOF is out of scope, pointing to related IEEE work (i.e., 802.1CB) 3, fixing the POF section and its configuration via controller plane


Question: EDHOC data and the OSCORE ciphertext, using the newly defined EDHOC option for signalling. <del> 4. The approach defined in this specification consists of sending EDHOC message_3 inside an OSCORE protected CoAP message. The resulting EDHOC + OSCORE request is in practice the OSCORE Request from fig-non-combined, sent to a protected resource and with the correct CoAP method and options, with the addition that it also transports EDHOC message_3. Since EDHOC message_3 may be too large to be included in a CoAP Option, e.g. if containing a large public key certificate chain, it has to be transported through the CoAP payload. The use of this approach is explicitly signalled by including an EDHOC Option (see signalling) in the EDHOC + OSCORE request. 4.1. </del> <ins> 5.2. </ins> The Client prepares an EDHOC + OSCORE request as follows.

Clean-up after URL As the content-from-edhoc branch seems to be the most up-to-date one (in which the parts changed are introduced in the first place), this builds on , and only the latest commit is actually relevant.
Compared to the original bstridentifier mapping, this is a different int-to-bstr mapping, but one that's most likely efficient to implement. I have not made any statement on the efficiencies, but some guidance we could give is that from a coding density point of view, numeric Cx should only be used with -24..23; for all other values, doing it in a bstr is just as good and saves a byte in OSCORE. (In fact we may want to make that normative, so that only the single-byte case needs to be implemented where this needs explicit implementation).


Question: The "a=rtcp-mux" line MUST only be added if present in the most recent answer. <del> The "a=rtcp-mux-only" line MUST only be added if present in the most recent answer. </del> The "a=rtcp-rsize" line MUST only be added if present in the most recent answer.

I applied the following principles, which unfortunately are somewhat inconsistent with the current mux-exclusive draft. You use a=rtcp-mux to negotiate mux a=rtcp-mux-only is used by the offerer to say "I really mean it" To that end, offers contain a=rtcp-mux-only if the policy is require. Answers don't contain it because you don't need it to negotiate mux.
Those principles are consistent with bundle-only, although I wrote the mux-only examples as if mux-only should always be included whenever a=rtcp-mux is present.
NAME back at you
NAME ping
LG


Question: When the multipath option is negotiated, clients that want to use an additional path MUST first initiate the Address Validation procedure <del> with PATH_CHALLENGE and PATH_RESPONSE frames described in Section 8 of QUIC-TRANSPORT.  After receiving packets from the client on the new paths, the servers MAY in turn attempt to validate these paths using the same mechanisms. </del> <ins> with PATH_CHALLENGE and PATH_RESPONSE frames described in Section 8.2 of QUIC-TRANSPORT.  After receiving packets from the client on a new path, if the server decides to use the new path, the server MUST perform path validation Section 8.2 of QUIC-TRANSPORT unless it has previously validated that address. </ins> If validation succeed, the client can send non-probing, 1-RTT packets on the new paths.  In contrast with the specification in Section 9 of

Fix issue
In section 3.1, we wrote When the multipath option is negotiated, clients that want to use an additional path MUST first initiate the Address Validation procedure with PATHCHALLENGE and PATHRESPONSE frames described in of ]. After receiving packets from the client on the new paths, the servers MAY in turn attempt to validate these paths using the same mechanisms. With multipath, we cannot simply write that the server MAY validate the new path. There is a risk of a malicious client that operates as follows: client creates path from its own address, A. Path is validate by server client starts long download from server client creates a second path to server using a spoofed address, B client starts address validation for B but does not care about the response from the server client stops acknowledging packets over the first path to force the server to move packets to the second one and then opportunistically acknowledges packets that should have been sent by the server over that second packet (SPNS would probably make such an attack simpler than MPNS) We probably need to start working on the security considerations section of the draft.
This is already covered in the QUIC threat model. The server is supposed to validate new paths by sending a "path challenge" on that path, then waiting for a challenge response. If the client spoofs a path, it will never receive the challenge, and thus the server will never receive the response and will not validate the path. See section 8.2 of RFC 9000, path validation. Security section 21.1.3. Connection Migration states that "Path validation () establishes that a peer is both willing and able to receive packets sent on a particular path."
So yes, the current text should be "the servers MUST in turn attempt to validate these paths using the same mechanisms, as specified in {{ Section 8.2 of RFC9000 }}."
No, this should not be a MUST. It is true that the path MUST be validated before it can be used. However, just because the serve receives a new packet on a path, that doesn't automatically mean that the server has to start path validation. It could e.g. also decide to simply withdraw that packet.
Actually, this is also not right. This is what RFC9000 says (section 9): So I guess we should maybe not use normative language here but refer to section 9 in RFC9000 instead...?
Just submitted PR for this issue.


Question: 4.2. <del> The Obfuscated CID Algorithm makes an attempt to obscure the mapping of connections to servers to reduce linkability, while not requiring true encryption and decryption.  The format is depicted in the figure </del> <ins> The Stream Cipher CID algorithm provides cryptographic protection at the cost of additional per-packet processing at the load balancer to decrypt every incoming connection ID.  The CID format is depicted </ins> below. 4.2.1. <del> The configuration agent selects an arbitrary set of bits of the server connection ID that it will use to route to a given server, called the "routing bits".  The number of bits MUST have enough entropy to have a different code point for each server, and SHOULD have enough entropy so that there are many codepoints for each server. The configuration agent MUST NOT select a routing mask with more than 136 routing bits set to 1, which allows for the first octet and up to 2 octets for server purposes in a maximum-length connection ID. The configuration agent selects a divisor that MUST be larger than the number of servers.  It SHOULD be large enough to accommodate reasonable increases in the number of servers.  The divisor MUST be an odd integer so certain addition operations do not always produce an even number. The configuration agent also assigns each server a "modulus", an integer between 0 and the divisor minus 1.  These MUST be unique for each server, and SHOULD be distributed across the entire number space between zero and the divisor. 4.2.2. Upon receipt of a QUIC packet, the load balancer extracts the selected bits of the Server CID and expresses them as an unsigned integer of that length.  The load balancer then divides the result by the chosen divisor.  The modulus of this operation maps to the modulus for the destination server. Note that any Server CID that contains a server's modulus, plus an arbitrary integer multiple of the divisor, in the routing bits is routable to that server regardless of the contents of the non-routing bits.  Outside observers that do not know the divisor or the routing bits will therefore have difficulty identifying that two Server CIDs route to the same server. Note also that not all Connection IDs are necessarily routable, as the computed modulus may not match one assigned to any server.  These DCIDs are non-compliant as described above. 4.2.3. The server chooses a connection ID length.  This MUST contain all of the routing bits and MUST be at least 9 octets to provide adequate entropy. When a server needs a new connection ID, it adds an arbitrary nonnegative integer multiple of the divisor to its modulus, without exceeding the maximum integer value implied by the number of routing bits.  The choice of multiple should appear random within these constraints. The server encodes the result in the routing bits.  It MAY put any other value into bits that used neither for routing nor config rotation.  These bits SHOULD appear random to observers. 4.3. The Stream Cipher CID algorithm provides true cryptographic protection, rather than mere obfuscation, at the cost of additional per-packet processing at the load balancer to decrypt every incoming connection ID.  The CID format is depicted below. 4.3.1. </del> The configuration agent assigns a server ID to every server in its pool, and determines a server ID length (in octets) sufficiently large to encode all server IDs, including potential future servers.

by popular demand in .
As discussed at IETF 108. Split from .
Thanks for filing this. I agree that this was the feedback, but I'll take it from the list to be sure.
Removing this seems fine to me.
Yes, do it.
Seems fine.
Do it.
Do it.
Nick Harper concurred on the list
Yes, that works. Minor comment.


Question: the ICE candidate event.  If the pool becomes depleted, either because a larger-than-expected number of ICE components is used, or because the pool has not had enough time to gather candidates, the <del> remaining candidates are gathered as usual. </del> <ins> remaining candidates are gathered as usual.  This only occurs for the first offer/answer exchange, after which the candidate pool is emptied and no longer used. </ins> One example of where this concept is useful is an application that expects an incoming call at some point in the future, and wants to

The pool is only used in the first offer/answer exchange. After applying a local description, the pool size is frozen and changing the ICE servers will not result in new candidates being pooled. After an answer is applied, any leftover candidates are discarded. This only happens when applying an answer so that candidates aren't prematurely discarded for use cases that involve pranswer, or multiple offers.
I can live with this as is. Want to read again if we end up making changes to address EKR comments
Updated PR and its description based on our discussion.


Question: 4.1.2. <del> Branch types must occur in a specific order relative to one another to avoid creating leaf nodes with invalid or incompatible settings. In the example above, it would be invalid to branch for derived endpoints (the DNS results for www.example.com) before branching between interface paths, since there are situations when the results will be different across networks due to private names or different supported IP versions.  Implementations must be careful to branch in an order that results in usable leaf nodes whenever there are multiple branch types that could be used from a single node. The order of operations for branching should be: Alternate Paths </del> <ins> Branch types ought to occur in a specific order relative to one another to avoid creating leaf nodes with invalid or incompatible settings.  In the example above, it would be invalid to branch for derived endpoints (the DNS results for www.example.com) before branching between interface paths, since there are situations when the results will be different across networks due to private names or different supported IP versions.  Implementations need to be careful to branch in a consistent order that results in usable leaf nodes whenever there are multiple branch types that could be used from a single node. This document recommends the following order of operations for branching: Network Paths </ins> Protocol Options

SORRY I made a PR on your PR, when I meant to leave a review comment, see 1024. .... Silly to make a PR on a PR - I added a review comment instead...
In section 4.1.4 in the impl draft, we have: "The order of operations for branching, where lower numbers are acted upon first, should be: Alternate Paths Protocol Options Derived Endpoints" However, I would say there is not really a strict ordering required. The text actually indicates that selection of the protocol is rather independent while there is usually a dependency between the interface and derived endpoint. I think this is related to my other issue about the use of the term path, because a path consists of both the local and remote endpoint and therefore there is of course a dependency. So in summary I'm not sure how useful I find this whole section as currently written...
We should conclude if anything more is needed here besides cleaning up the terminology, where Alternate Paths is not a good term - see .
Any implementation should have a consistent order of operations. This is a recommended example. Reference the arch text that says it needs to work the same way each time.
Reference ICE/HE


Question: to use smaller packets, so that the limited reassembly capacity is not exceeded. <del> For TCP, MSS clamping (Section 3.2 of {?RFC4459}}) is often used to </del> <ins> For TCP, MSS clamping (Section 3.2 of RFC4459) is often used to </ins> change the sender's maximum TCP segment size, but QUIC requires a different approach.  Section 14 of QUIC-TRANSPORT advises senders to probe larger sizes using Datagram Packetization Layer PMTU Discovery

Some section refs weren't linked to the sections; some objects were defined multiple ways; one reference wasn't actually cited in the text.
Thanks a lot!


Question: be acknowledged, an endpoint MAY wait until an ack-eliciting packet has been received to include an ACK frame with outgoing frames. <ins> A receiver MUST NOT send an ack-eliciting frame in all packets that would otherwise be non-ack-eliciting, to avoid an infinite feedback loop of acknowledgements. </ins> 13.2.2. A receiver determines how frequently to send acknowledgements in

It's no longer normative and it's in a single section. I only moved text so far, and not as far as NAME suggested. I can go farther here or in a follow-up PR.
NAME I would like to merge this. WDYT?
Can we merge this soon. I'm worried about it developing conflicts.
Yep, NAME lost the chance to fix the PR. We are - of course - still open for editorial improvements in the form of new pull requests though.
calls them "exemplary" but 13.2.4 has MUST in it.
For reference, this refers to and in the editor's copy. I'm in favour of striking the exemplary note and saying that while the recovery draft is advisory, this document depends on implementations following something like what is recommended.
The specific MUSTs aren't really about the ACK algorithm per se, but about state endpoints will have to maintain for other reasons that are typically folded into your loss recovery code. If an implementation is unable to do duplicate detection for a packet number range, it MUST fail toward rejecting all packets, not toward accepting potential duplicates. An implementation must track the greatest packet number ever received, for use in recovering future packet numbers. In fact, the first requirement is discussed in 12.3 and could probably be dropped here. The second isn't actually called out (MUST) in 17.1, but could easily be moved there.
I think I'm inclined towards reorganizing the text and putting all the 'exemplary' parts into one section(ie: "Limiting ACK Ranges") and moving the normative text either into "Managing ACK Ranges" or elsewhere in the draft.
I thought I could clean this up fairly quickly, but I think a fair number of paragraphs need to move, including some of NAME suggestions. I'm happy to try to improve this in a few days if no one else has beaten me to it.
Anyone want to help NAME out and take this on?
Sorry about dropping this one. I'm fine with it, and happy to make editorials one later.Thanks Ian. When you lay it out like this, it seems so obvious. I checked that we don't have citations for {{ack-tracking}}, so this works nicely. If you care about the "MAY", then we can fix that in another PR.


Question: 3.2. <del> The properties specified during pre-establishment has a close </del> <ins> The properties specified during pre-establishment have a close </ins> connection to system policy.  The implementation is responsible for combining and reconciling several different sources of preferences when establishing Connections.  These include, but are not limited to: Application preferences, i.e., preferences specified during the <del> pre-establishment such as Local Endpoint, Remote Endpoint, Path Selection Properties, and Protocol Selection Properties. </del> <ins> pre-establishment via Selection Properties. </ins> Dynamic system policy, i.e., policy compiled from internally and externally acquired information about available network

Several small updates, mostly to clean things up a bit, and align property names and such.
NAME - I think you're wrong: my understanding (and also the way the text is written - otherwise we'd have to change it in the API draft) was that Connection Properties can (and should) also be set on Preconnections, to give as much input as possible for Connection establishment. In the API draft, the Selection Properties in Section 5.2 can only be used on Preconnections: you can't ask for congestion control after establishment. You can't say that you'd rather have multistreaming support after establishment. But that doesn't exclude Connection properties from being usable earlier. Required minimum checksum coverage could influence choosing UDP-Lite vs. UDP. Bounds on Send or Receive Rate could influence the interface choice. The capacity profile could influence various things (and no, there isn't a matching Selection Property now - there is a per-Message override). So... I think that either you're wrong, or I'm missing something and the API draft heavily lags behind a decision that was made. I hope not!
NAME The API drafts says: I interpret this as only the Selection Properties influence selection and the Connection properties are used to further configure the connections according to user preferences. Otherwise what is the difference between them?
If you interpret it as you do, I think the text isn't clear enough (indeed it isn't super clear - in particular, "eventually established" is misleading IMO). Though, note that it says that Connection properties can also be used later. Regarding the difference between them: Selection Properties only make sense for Preconnections.
NAME - sorry lost this thread. But I saw that you have started cleaning up some Connection properties that had mixed Connection and Selection properties up in the API draft. Does it mean that we are now in synch and agree that only Selection properties are used in the selection and Connection properties are used for configuration (both during establisment and also after the connection setup).
NAME the other PR means nothing about what I said here: it only tried to address issue which is about a wording inconsistency in a specific property. You say that Connection properties can also be used during establishment - if you agree with allowing this, then why not allow to configure them as early as possible and allow them to influence selection?


Question: 3.2. <del> The properties specified during pre-establishment has a close </del> <ins> The properties specified during pre-establishment have a close </ins> connection to system policy.  The implementation is responsible for combining and reconciling several different sources of preferences when establishing Connections.  These include, but are not limited to: Application preferences, i.e., preferences specified during the <del> pre-establishment such as Local Endpoint, Remote Endpoint, Path Selection Properties, and Protocol Selection Properties. </del> <ins> pre-establishment via Selection Properties. </ins> Dynamic system policy, i.e., policy compiled from internally and externally acquired information about available network

What's bad about having more information available that can guide the selection process?
NAME the problem is that the Connection properties are not expressed in a way suitable for selection. If they should also be used for Selection they would have to be reworked to be of type Preference. Otherwise I do not know what they mean for selection. What does it mean if I pick say a particular connection group transmission scheduler? Is it required or preferred? Most connection properties also do not look very useful to me for selection so in case there are some we need I think it would be simpler to just define a matching selection property.
NAME we're only discussing whether it's allowed to use them as additional input or not. I agree, some (like the scheduler choice) don't seem useful, but some do... generally we may not have good guidance on how they should be used by an implementation, but giving the system freedom to use as many inputs as possible is probably a good thing. Regarding the type, require/prefer//ignore/avoid/prohibit obviously works fine for a "wishlist" of boolean character: having something, or not having it. The selection properties are generally like that - except "Interface Instance or Type" and "Provisioning Domain Instance or Type" which are, well... wishlist-collections. Consider the capacity profile. Surely configuring this early can be useful input - e.g. if someone picks low latency / interactive, you may even want to put this traffic on a specific network interface! But if you'd want to make a copy of the capacity profile as a "proper" selection property, how would you do it? Apply require/prefer/ignore/avoid/prohibit for each of its values? Then I could say "prefer" low latency/non-interactive but "avoid" low latency/non-interactive, which would surely be odd. Apply the qualifier to the whole thing? Then it's about, e.g. "avoiding" to use a capacity profile at all. That's odd as well. I think it's in the nature of the current selection properties that they merely say "I want to be able to do this, and this is how important it is to me", which is different from configuring something. That's also why, as written, they simply wouldn't work for later connection configuration.


Question: 3.2. <del> The properties specified during pre-establishment has a close </del> <ins> The properties specified during pre-establishment have a close </ins> connection to system policy.  The implementation is responsible for combining and reconciling several different sources of preferences when establishing Connections.  These include, but are not limited to: Application preferences, i.e., preferences specified during the <del> pre-establishment such as Local Endpoint, Remote Endpoint, Path Selection Properties, and Protocol Selection Properties. </del> <ins> pre-establishment via Selection Properties. </ins> Dynamic system policy, i.e., policy compiled from internally and externally acquired information about available network

Connection properties really are about configuring something, but I still say that being able to use them as early input is good. I agree that the implementation isn't super clear as they don't come with a require/prefer/... etc. qualifier, but then we just offer some freedom to implementers.
NAME I just pushed a commit that updates the selection and connection properties text, removing "connection" almost everywhere, but adding a disclaimer in the beginning that says that connection properties should be configured as early as possible because they can influence decisions made by the implementation, and "In the remainder of this document, we only refer to Selection Properties because they are the more typical case." Frankly I'm not sure this is better... but it does remove most of the "selection and connection" double mentions that you pointed out.
Fixed up branch building and resolved merge conflicts. I'll merge this in later today before the posting deadline.
Cool thanks! Sorry if I messed something up
As discussed in
Thank you for updating this – looks good! just needs s/send-params/msg-properties/ and merging


Question: addresses on a single link.  In such cases, identification could be performed by subnet, such as the /64 to which the IP belongs. <del> 3.4.3. The URIs provided in the API SHOULD contain all the information necessary to render the resources requested: the resources should not depend on ambient information, such as remote address on the connection.  This is to ensure that the content served from these URIs is correct and meaningful to the User Equipment, even when accessed from a network other than the one that contains the captive portal.  One consequence of this is that URIs provided in the API are expected to be resolved using public global DNS (as defined in Section 2 of RFC8499). </del> <ins> 3.5. A Captive Portal API needs to present information to clients that is unique to that client.  To do this, some systems use information from the context of a request, such as the source address, to identify the UE. Using information from context rather than information from the URI allows the same URI to be used for different clients.  However, it also means that the resource is unable to provide relevant information if the UE makes a request using a different network path. This might happen when UE has multiple network interfaces.  It might also happen if the address of the API provided by DNS depends on where the query originates (as in split DNS RFC8499). Accessing the API MAY depend on contextual information.  However, the URIs provided in the API SHOULD be unique to the UE and not dependent on contextual information to function correctly. </ins> Though a URI might still correctly resolve when the UE makes the request from a different network, it is possible that some functions

This rewrites the context-free URI section to give more context. It also moves the section out from underneath the example identifiers section, and into a proper sub-section of the top level "User Equipment Identity" section. Closes issue
NAME , I mostly took your text word-for-word. Thanks for it!
A reviewer writes, I think this is trying to say the server should not be looking at Ethernet addresses, for example, because the server is probably not on the same subnet as the User Equipment. So the info needs to be in the URL. Figure out what we're trying to say, and whether this is the right section for it.
That's exactly what it's talking about. That said, while it is related to identifying the UE, it's not an example identifier. It has been a while since I thought about this, and I wasn't at the meeting where it was discussed, but I think the intention here was to limit any URIs provide in the API to these context-free URIs. That is, the resource pointed to by the URI cannot depend on information not present in the URI. For example, the API draft (URL) provides a 'user-portal-url'. Suppose that URL is "captive-URL". That resource could be implemented by checking the source ethernet address of the connection to see if you're already logged in. But, that won't be correct if you're not in the same subnet. Instead, the URL should be something like: "captive-URL" So, this is more of a constraint on the API and how it uses identifiers than an example of an identifier. Did we just get the indentation wrong? Or was this a misunderstanding of what the working group requested?
Maybe all this needs is a preface explaining how some systems operate. The last two paragraphs are a direct copy of existing text.
Hardly surprising that I think this is OK :)


Question: Section 4.4 of IANA-POLICY) where two registrations MUST NOT have the same Key.  This registry is initially empty. <del> 10.  References </del> <ins> 9.  References </ins> <del> 10.1.  URIs </del> <ins> 9.1.  URIs </ins> [1] mailto:masque@ietf.org

This PR aims to take the design discussions we had at the last interim, and propose a potential solution. This PR should in theory contain enough information to allow folks to implement this new design. That will allow us to perform interop testing and confirm whether the design is sound.
I'm confused by this pull request (probably because I was out of the loop for a while). My understanding, at least when I first read the proposal a month ago was that we would separate multiplexing streams and multiplexing contexts into different layers, so that methods that need context would get it (CONNECT-UDP), and features that don't (WebTransport/extended CONNECT) could use stream-associated datagrams directly.
NAME you're referring to which this PR isn't trying to address. That'll happen in a subsequent PR.
In , capsules, contexts and context IDs are explicitly defined as end-to-end and there are requirements for intermediaries to not modify them, and to not even parse them. The motivation for this was to ensure that we retain the ability to deploy extensions end-to-end without having to modify intermediaries. NAME mentioned that these requirements might be too strict, as he would like to have his intermediary be able to parse the context ID, for logging purposes.
Part of the comment from the PR is also about consistency of interface for generic HTTP libraries that can be used to build either endpoints or intermediaries. If the context ID is always present, it's overly prescriptive to say that an intermediary can't parse it, and such a requirement couldn't be enforced anyways. If context IDs are negotiated on/off, whether this is possible depends on the negotiation mechanism.
I think its fine for a component that has bytes passing through it to look at those bytes. The import thing to do is set expectations on what that means for the protocol behaviour we are defining. We don't expect intermediaries to do anything with a context ID; they should not enforce the protocol semantic rules (odd, even, reuse etc). H2 and H3 somewhat solve this problem by decoupling frame parsing from frame payload interpretation. E.g. if the form of a request or response is invalid, an intermediary shouldn't pass it on. DATAGRAM is different because it isn't defined as an actual HTTP/3 frame with frame headers and frame payload.


Question: Section 4.4 of IANA-POLICY) where two registrations MUST NOT have the same Key.  This registry is initially empty. <del> 10.  References </del> <ins> 9.  References </ins> <del> 10.1.  URIs </del> <ins> 9.1.  URIs </ins> [1] mailto:masque@ietf.org

Something that might work is to formalise that quarter stream ID is part of the envelope that intermediaries have to be able to handle the syntax of, but context ID is part of content and separate.
Unless you encrypt capsules end-to-end, I don't think any text in the spec can in practice prevent intermediaries from inspecting and modifying capsules. You can send something like GREASE capsules, though.
In , we introduce the CLOSEDATAGRAMCONTEXT capsule which allows endpoints to close a context. That message currently only contains the context ID to close. NAME suggests that we may want to add more information there. Should we differentiate between "context close" and "context registration rejected"? Should we add an error code? In particular, do folks have use cases for these features?
My first concern is with infinite loops. If the context was "garbage collected" by the recipient, the sender can simply re-create it if they still want it. However, if it was closed due to incompatibility (i.e. rejected) or hitting a resource limit (e.g. max # of contexts), reopening it in response will produce a tight infinite loop. This could be maybe be avoided by some kind of heuristic, but an explicit indication of what's going on seems better.
This issue assumes that decide to go with the two-layer design described in . Given that design, some applications might not need the multiplexing provided by context IDs. We have multiple options here: Make context ID mandatory Applications that don't need it waste a byte per datagram Negotiate the presence of context IDs using an HTTP header Context IDs would still be mandatory to implement on servers because the client might send that header Have the method determine whether context IDs are present or not This would prevent extensibility on those methods Create a REGISTERNOCONTEXT message This assumes we use the Message design from We add a register message that means that this stream does not use context IDs This allows avoiding the byte overhead without sacrificing extensibility
Making the context ID mandatory is simple, although slightly wasteful. For the variations where it is optional, I prefer the one that uses a header. It could work with a variant of where we do Header + Message, and the Header determines whether or not you have contexts, and whether or not they can be dynamic.
What are the benefits of message over header to make it optional?


Question: Section 4.4 of IANA-POLICY) where two registrations MUST NOT have the same Key.  This registry is initially empty. <del> 10.  References </del> <ins> 9.  References </ins> <del> 10.1.  URIs </del> <ins> 9.1.  URIs </ins> [1] mailto:masque@ietf.org

To me it seems like header is sufficient, because the context IDs are end-to-end, and should not affect intermediaries, making the header a natural place to put it. I think having the context ID be the default behavior and the header is to opt-out is the right decision if we were to allow removing it.
This is a bit of a bike-shed, but why would it default to having context-IDs instead of not having them?
I think the second option "Negotiate the presence of context IDs using an HTTP header" is the best personally. In terms of: "Context IDs would still be mandatory to implement on servers because the client might send that header", I assume server in this context is the final application server, not a proxy? Even so, I'd argue it's applications which decide if they need this functionality, so if a server only implemented one application and it didn't use Context-IDs, then I don't see why it would need to implement it.
Ian, in your comment, are you talking about an intermediary when you say "proxy"? If so, then an intermediary need not implement anything based on the payload of than H3 DATAGRAM, it only has to pass the data along. That may be worth a clarification.
Having context ID optional has a nice future-proof property - other uses of datagrams in HTTP/3 can decide if they want the second layer or not. I wouldn't even state it as application needing multiplexing or not. Other applications might find it very useful to include a second ((third, fourth, fifth) layer of frame header. I think its fine for us to state as much in this in the spec, while also defining an explicit second layer for multiplexing.
Yes, by proxy I meant intermediary. And I agree about what intermediaries need to do, I just wanted to ensure I understood what server meant when David used it above. Yup, whenever all this gets written up, we can make it clear that intermediaries can ignore much of this.
The method defines the semantics of datagrams for a particular request, thus I think the third option makes most sense.


Question: Section 4.4 of IANA-POLICY) where two registrations MUST NOT have the same Key.  This registry is initially empty. <del> 10.  References </del> <ins> 9.  References </ins> <del> 10.1.  URIs </del> <ins> 9.1.  URIs </ins> [1] mailto:masque@ietf.org

I don't see a point in using explicit negotiation, since in the two cases I can think of the top of the head, the answer is always clear from the method (CONNECT-IP seems to always want context IDs, WebTransport does not ever want context IDs). If some method starts out without context, but wants to add context later, it can add its own negotiation.
One set of use cases for which the method approach(3) is best are those where there are multiple context IDs but they're predefined by the method and don't need negotiation. My strawman is WebRTC.
During the 2021-04 MASQUE Interim, we discussed multiple options for registering context IDs. Without going into the specific of the encoding, there are two broad classes of solutions: "Header" design Once-at-setup registration This happens during the HTTP request/response Simplest solution is to use an HTTP header such as (encoding TBD) Example use-case: CONNECT-UDP without extensions "Message" design Mid-stream registration This can happen at any point during the lifetime of the request stream This would involve some sort of "register" message (encoding TBD, see separate issue) Example use-case: CONNECT-IP on-the-fly compression (this can't be done at tunnel setup time because the bits top be compressed aren't always known at that time) It's possible to implement once-at-setup registration using the Message design, but it isn't possible to implement mid-stream registration. Therefore I think we should go with the Message design. It would also be possible to implement both but I don't think that provides much value.
I'd like to here some more from the WebTransport use case on the issue. My understanding is that the Requests are used to create WebTransport sessions and that creation of datagram flows(contexts) could be a lot more ad-hoc / server generated after the request phase, when compared to the CONNECT-UDP case. Cc NAME
Personally, I'd vote for either "message" or "message + header" (a la priorities), but not just "header". Mid-stream annotation of context/flow/etc is quite useful.
I prefer "Message" only, since the dynamic use case seems like a fairly compelling use of sub-flows(contexts?).


Question: Section 4.4 of IANA-POLICY) where two registrations MUST NOT have the same Key.  This registry is initially empty. <del> 10.  References </del> <ins> 9.  References </ins> <del> 10.1.  URIs </del> <ins> 9.1.  URIs </ins> [1] mailto:masque@ietf.org

I'm not sure there are many cases when one allocates all sub-flows up front AND needs to use a header to do that in a flexible way. If an application needs multiple sub-flows, but they're fixed in number/format(ie: data and control), I don't think there's a need for a header or a "Message", since the application can consider that part of its internal format.
During the 2021-04 MASQUE Interim, we discussed having the ability to accept or reject registration of context IDs. An important motivation for this is the fact that context ID registrations take up memory (for example it could be a compression context which contains the data that is elided) and therefore we need to prevent endpoints from arbitrarily making their peer allocate memory. While we could flow control context ID registration, a much simpler solution would be to have a way for endpoints to close/shutdown a registration.
IIUC there's an opposing view that the constraints can be negotiated apiori. Either statically (such as defining an extension which states that there can only be N contenxts of a given type) or dynamically using something like a HTTP header. Failure to meet these constraints could lead to an HTTP/3 stream or connection error rather than a flow rejection.
NAME I've filed to discuss whether to register/negotiate at request start or mid-stream.
I think that if there is the ability to register mid-stream (), we need the ability to close/de-register/reject mid-stream as well. If we don't have mid-stream changes, then no need to negotiate. However, someone trying to register something needs to be able to know whether or not the thing they registered will be accepted.
I agree that notification of the registration status is particularly important if we allow mid-stream registration.
In draft-ietf-masque-h3-datagram-00, flow IDs are bidirectional. During the 2021-04 MASQUE Interim, we discussed the possibility of making them unidirectional. Here are the differences: Bidirectional single shared namespace for both endpoints (even for client, odd for server) it's easier to refer to peer's IDs, which makes negotiation easier Unidirectional one namespace per direction every bidirectional use needs to associate both directions somehow I'm personally leaning towards keeping them bidirectional.


Question: Section 4.4 of IANA-POLICY) where two registrations MUST NOT have the same Key.  This registry is initially empty. <del> 10.  References </del> <ins> 9.  References </ins> <del> 10.1.  URIs </del> <ins> 9.1.  URIs </ins> [1] mailto:masque@ietf.org

Unlike QUIC streams, these do not have a state machine or flow control credits, so there is no cost to only using a single direction of a bidirectional flow for unidirectional use-cases.
There's another option where flows are unidirectional but they share a namespace (cleint even/server odd). I'm undecided. And I also don't know how important it is to choose. The 2 layer design means that DATAGRAMs always have a bidirectional tie via the stream ID. On balance, I think bidirectional would be good enough today but I would be receptive to extension use cases that make a strong point of unidirectional.
Bidirectional is my personal preference, but either way could work ultimately. It seems to me that any extension that wants unidirectional can just only use this context/flow/etc ID for one direction if it wants.
I think bidirectional flows are likely overcomplicated and unnecessary. For example, if either peer can "close" a flow, this requires a much more complex state machine. In my experience, half-closed states are hard to get right. Closing unidirectional flows seems much easier to reason about. Many, perhaps most, of our use cases for flows are really unidirectional. For example, DSCP marking likely only makes sense from client to server, while timestamps for congestion control tuning likely only make sense from server to client. QUIC connection IDs are different in each direction, so QUIC header compression may be easiest to understand with unidirectional flows.
Bidirectional doesn't imply half-close states. I'm thinking of a bidirectional flow that can only be closed atomically as a whole. I don't think that's true. The default extension-less CONNECT-UDP is bidirectional. So is ECN, and so would a timestamp extension.
I would prefer bidirectional without support for half-close. I feel that having unidirectional flow/context IDs adds overhead we don't need; peers now need to track those associations and it's unclear what the benefits of having them separated out are.
This issue is conflating consent (unilateral/bilateral) with scope (unidirectional/bidirectional). IIUC there are two questions here: 1) Can I send a flow-id forever once declared, or can the endpoint tell me to stop without killing the whole stream (consent)?


Question: Section 4.4 of IANA-POLICY) where two registrations MUST NOT have the same Key.  This registry is initially empty. <del> 10.  References </del> <ins> 9.  References </ins> <del> 10.1.  URIs </del> <ins> 9.1.  URIs </ins> [1] mailto:masque@ietf.org

2) Can the receiver of a flow-id assignment use that same flow-id when sending datagrams, or could this mean something completely different? I think the answer to (1) is "yes, it can tell me to stop" (i.e. it is negotiated while allowing speculative sending). For (2), I lean toward bidirectional, but not strongly. There are plenty of codepoints, so it seems wasteful for each endpoint to define the same semantic explicitly.
NAME the intent of this issue wan't to conflate those two things. This issue is about scope. For consent, see issue .
Conceptually, I like unidirectional better. I tell the peer that when I send with context-ID=X, it has a given semantic. For bidirectional the sender is saying both that and that if the peer sends on that ID the original sender will interpret with the same semantic. That might not even make sense. Is it possible to associate datagrams with a unidirectional stream (push?). If so, does allowing for bidirectional context imply that even though the receiver cannot send frames on the stream, it can send datagrams? Every negotiation does run the risk of loss/reordering resulting in a drop or buffering event at the receiver. The appeal of bidirectional is that it removes half of this risk in the cases where the bidirectionality is used.
To second NAME I would also prefer bidirectional without support for half-close. Given you can always not send something in one direction, and there's none of the overhead of streams(ie: flow control, etc) I can't see any benefits of unidirectional over bidirectional in this case. Associating h3-datagrams with a server push seems like unnecessary complexity to me, but you're right that it should be clarified.
During the 2021-04 MASQUE Interim, we discussed a design proposal from NAME to replace the one-layer flow ID design with a two-layer design. This design replaces the flow ID with two numbers: a stream ID and a context ID.


Question: Section 4.4 of IANA-POLICY) where two registrations MUST NOT have the same Key.  This registry is initially empty. <del> 10.  References </del> <ins> 9.  References </ins> <del> 10.1.  URIs </del> <ins> 9.1.  URIs </ins> [1] mailto:masque@ietf.org

The contents of the QUIC DATAGRAM frame would now look like: While the flow ID in the draft was per-hop, the proposal has better separation: the stream ID is per-hop, it maps to an HTTP request the context ID is end-to-end, it maps to context information inside that request Intermediaries now only look at stream IDs and can be blissfully ignorant of context IDs. In the room at the 2021-04 MASQUE Interim, multiple participants spoke in support of this design and no one raised objections. This issue exists to ensure that we have consensus on this change - please speak up if you disagree.
I am fine with the 2-layer design for CONNECT-UDP, but I am not sure if the second identifier should be in H3 DATAGRAM or should be specific to CONNECT-UDP. As I indicated to the list, webtrans and httpbis might weigh in on this with broader consideration of other use cases.
Hi NAME the topic of the optionality of context IDs is discussed in issue .
I think this is a good design, because it minimizes the core functionality of the draft, but avoids every application that needs multiple dynamically created sub-flows from re-inventing a different mechanism. Nit: I would not call this a 'Frame', since it's not an HTTP(TLV) frame.
I think this is a good change. Thanks! There are some things that I think we should still discuss, but we shouldn't hold up this change on those details.