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Fix #200

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This commit is contained in:
Luke Parker 2023-03-07 03:55:58 -05:00
parent 5a9a42f025
commit 2bad06e5d9
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1 changed files with 11 additions and 1 deletions
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12
crypto/transcript/src/lib.rs
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@ -50,6 +50,8 @@ enum DigestTranscriptMember {
Label,
Value,
Challenge,
Continued,
Challenged,
}
impl DigestTranscriptMember {
@ -60,6 +62,8 @@ impl DigestTranscriptMember {
DigestTranscriptMember::Label => 2,
DigestTranscriptMember::Value => 3,
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 {
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] {