This commit is contained in:
Luke Parker
2023-03-07 03:55:58 -05:00
parent 5a9a42f025
commit 2bad06e5d9

View File

@@ -50,6 +50,8 @@ enum DigestTranscriptMember {
Label, Label,
Value, Value,
Challenge, Challenge,
Continued,
Challenged,
} }
impl DigestTranscriptMember { impl DigestTranscriptMember {
@@ -60,6 +62,8 @@ impl DigestTranscriptMember {
DigestTranscriptMember::Label => 2, DigestTranscriptMember::Label => 2,
DigestTranscriptMember::Value => 3, DigestTranscriptMember::Value => 3,
DigestTranscriptMember::Challenge => 4, DigestTranscriptMember::Challenge => 4,
DigestTranscriptMember::Continued => 5,
DigestTranscriptMember::Challenged => 6,
} }
} }
} }
@@ -110,7 +114,13 @@ impl<D: Clone + SecureDigest> Transcript for DigestTranscript<D> {
fn challenge(&mut self, label: &'static [u8]) -> Self::Challenge { fn challenge(&mut self, label: &'static [u8]) -> Self::Challenge {
self.append(DigestTranscriptMember::Challenge, label); self.append(DigestTranscriptMember::Challenge, label);
self.0.clone().finalize() let mut cloned = self.0.clone();
// Explicitly fork these transcripts to prevent length extension attacks from being possible
// (at least, without the additional ability to remove a byte from a finalized hash)
self.0.update([DigestTranscriptMember::Continued.as_u8()]);
cloned.update([DigestTranscriptMember::Challenged.as_u8()]);
cloned.finalize()
} }
fn rng_seed(&mut self, label: &'static [u8]) -> [u8; 32] { fn rng_seed(&mut self, label: &'static [u8]) -> [u8; 32] {