Re: [quicwg/base-drafts] Pad rather than shift the header protection offset (#2030)

[Martin Thomson <[e-mail]>]

martinthomson commented on this pull request.



> -is assumed to be 4 bytes long (its maximum possible encoded length), unless
-there is insufficient space in the packet for a complete sample.  The starting
-offset for the sample is set to 4 bytes after the start of the Packet Number
-field, then is reduced until there are enough bytes to sample.
+is assumed to be 4 bytes long (its maximum possible encoded length).
+
+An endpoint MUST discard packets that are not long enough to contain a complete
+sample.
+
+To ensure that sufficient data is available for sampling, packets are padded so
+that the combined lengths of the encoded packet number and protected payload is
+at least 4 bytes longer than the sample required for header protection.  For the
+AEAD functions defined in {{?TLS13}}, which have 16 byte expansion and 16 byte
+header protection samples, this results in needing at least 3 bytes of frames in
+the unprotected payload if the packet number is encoded on a single byte, or 2
+bytes of frames for a 2 byte packet number encoding.

Good catch.

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