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58 lines
2.2 KiB
Rust
58 lines
2.2 KiB
Rust
use core::fmt::{Debug, Formatter};
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use crate::Transcript;
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/// A wrapper around a Merlin transcript which satisfiees the Transcript API.
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///
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/// Challenges are fixed to 64 bytes, despite Merlin supporting variable length challenges.
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///
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/// This implementation is intended to remain in the spirit of Merlin more than it's intended to be
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/// in the spirit of the provided DigestTranscript. While DigestTranscript uses flags for each of
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/// its different field types, the domain_separate function simply appends a message with a label
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/// of "dom-sep", Merlin's preferred domain separation label. Since this could introduce transcript
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/// conflicts between a domain separation and a message with a label of "dom-sep", the
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/// append_message function uses an assertion to prevent such labels.
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#[derive(Clone)]
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pub struct MerlinTranscript(merlin::Transcript);
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// Merlin doesn't implement Debug so provide a stub which won't panic
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impl Debug for MerlinTranscript {
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fn fmt(&self, fmt: &mut Formatter<'_>) -> Result<(), core::fmt::Error> {
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fmt.debug_struct("MerlinTranscript").finish_non_exhaustive()
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}
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}
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impl Transcript for MerlinTranscript {
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// Uses a challenge length of 64 bytes to support wide reduction on commonly used EC scalars
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// From a security level standpoint (Merlin targets 128-bits), this should just be 32 bytes
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// From a Merlin standpoint, this should be variable per call
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// From a practical standpoint, this should be practical
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type Challenge = [u8; 64];
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fn new(name: &'static [u8]) -> Self {
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MerlinTranscript(merlin::Transcript::new(name))
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}
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fn domain_separate(&mut self, label: &'static [u8]) {
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self.0.append_message(b"dom-sep", label);
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}
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fn append_message<M: AsRef<[u8]>>(&mut self, label: &'static [u8], message: M) {
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assert!(
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label != "dom-sep".as_bytes(),
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"\"dom-sep\" is reserved for the domain_separate function",
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);
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self.0.append_message(label, message.as_ref());
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}
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fn challenge(&mut self, label: &'static [u8]) -> Self::Challenge {
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let mut challenge = [0; 64];
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self.0.challenge_bytes(label, &mut challenge);
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challenge
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}
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fn rng_seed(&mut self, label: &'static [u8]) -> [u8; 32] {
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let mut seed = [0; 32];
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seed.copy_from_slice(&self.challenge(label)[.. 32]);
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seed
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}
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}
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