Clarify that DTLS uses the DTLS HKDF-Expand-Label #641
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We've made a mess of things and now every extension that cites HKDF-Expand-Label needs to clarify this. This seems like a mistake. Worse, if a future TLS 1.4 change the "tls13" prefix to "tls14", every extension will now become ambiguous! I've left that alone in this document, but we may need to contend with this later. In hindsight, we should have excluded the implicit "tls13 " prefix from the HKDF-Expand-Label function. Instead, the version-dependent labels could have been incorporated into individual labels as needed. (In particular, I don't think this label actually needed to be version-dependent.) Instead we seem to have implicitly decided that HKDF-Expand-Label is part of the "interface" that TLS exposes to its extensions, without remembering to say so clearly. Anyway, this PR does the minimal thing to paper over this mess.
This was referenced Dec 2, 2024
martinthomson
approved these changes
Dec 5, 2024
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@ekr,
@davidben is completely right here. That's something we've more or less assumed about TLS in QUIC. RFC 8446bis seems to be open still. Is this feasibly something we could fix there? (It's in AD evaluation, which is hardly so far gone as to make this sort of thing impossible.) |
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Yes, I think we could make this change as long as @paulwouters is OK with that. |
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It's fine with me, but please send a message to the TLS list with the change and reasoning quoted from this PR as an audit log to the IETF process. |
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(I made this into a separate PR from #640 just because I realized the ambiguity later and it seemed rude to change #640 after folks have already looked at it.)
We've made a mess of things and now every extension that cites HKDF-Expand-Label needs to clarify this. This seems like a mistake.
Worse, if a future TLS 1.4 change the "tls13" prefix to "tls14", every extension will now become ambiguous! I've left that alone in this document, but we may need to contend with this later.
In hindsight, we should have excluded the implicit "tls13 " prefix from the HKDF-Expand-Label function. Instead, the version-dependent labels could have been incorporated into individual labels as needed. (In particular, I don't think this label actually needed to be version-dependent.)
Instead we seem to have implicitly decided that HKDF-Expand-Label is part of the "interface" that TLS exposes to its extensions, without remembering to say so clearly.
Anyway, this PR does the minimal thing to paper over this mess.