[TLS] Ambiguity of TLS Certificate Compression (RFC 8879)

[Kazu Yamamoto (山本和彦)]

Hello,

Though implementation of certificate compression, I felt that 
RFC 8879 is ambiguous on how to calculate transcript hash.

RFC 8446 defines the content for Certificate Verify as follow:

   Transcript-Hash(Handshake Context, Certificate)

This is natural reuse of transcript hash. So, AFAIK, "tlsfuzzer" and
facebook.com use the following as the content:

   Transcript-Hash(Handshake Context, CompressedCertificate)

But RFC 8879 says:

   After decompression, the Certificate message MUST be processed as
   if it were encoded without being compressed.

I think the following original interpretation is possible for the
content:

   Transcript-Hash(Handshake Context, Certificate)

Clarification would be helpful.

--Kazu


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