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102 lines
3.2 KiB
Rust
102 lines
3.2 KiB
Rust
#![cfg_attr(docsrs, feature(doc_auto_cfg))]
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#![no_std]
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#[cfg(feature = "merlin")]
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mod merlin;
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#[cfg(feature = "merlin")]
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pub use crate::merlin::MerlinTranscript;
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use digest::{typenum::type_operators::IsGreaterOrEqual, consts::U256, Digest, Output};
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pub trait Transcript {
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type Challenge: Clone + Send + Sync + AsRef<[u8]>;
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/// Create a new transcript with the specified name.
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fn new(name: &'static [u8]) -> Self;
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/// Apply a domain separator to the transcript.
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fn domain_separate(&mut self, label: &'static [u8]);
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/// Append a message to the transcript.
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fn append_message(&mut self, label: &'static [u8], message: &[u8]);
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/// Produce a challenge. This MUST update the transcript as it does so, preventing the same
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/// challenge from being generated multiple times.
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fn challenge(&mut self, label: &'static [u8]) -> Self::Challenge;
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/// Produce a RNG seed. Helper function for parties needing to generate random data from an
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/// agreed upon state. Internally calls the challenge function for the needed bytes, converting
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/// them to the seed format rand_core expects.
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fn rng_seed(&mut self, label: &'static [u8]) -> [u8; 32];
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}
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enum DigestTranscriptMember {
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Name,
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Domain,
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Label,
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Value,
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Challenge,
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}
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impl DigestTranscriptMember {
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fn as_u8(&self) -> u8 {
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match self {
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DigestTranscriptMember::Name => 0,
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DigestTranscriptMember::Domain => 1,
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DigestTranscriptMember::Label => 2,
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DigestTranscriptMember::Value => 3,
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DigestTranscriptMember::Challenge => 4,
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}
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}
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}
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pub trait SecureDigest: Clone + Digest {}
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impl<D: Clone + Digest> SecureDigest for D where D::OutputSize: IsGreaterOrEqual<U256> {}
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/// A trait defining cryptographic Digests with at least a 256-byte output size, assuming at least
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/// a 128-bit level of security accordingly.
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/// A simple transcript format constructed around the specified hash algorithm.
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#[derive(Clone, Debug)]
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pub struct DigestTranscript<D: SecureDigest>(D);
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impl<D: SecureDigest> DigestTranscript<D> {
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fn append(&mut self, kind: DigestTranscriptMember, value: &[u8]) {
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self.0.update([kind.as_u8()]);
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// Assumes messages don't exceed 16 exabytes
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self.0.update(u64::try_from(value.len()).unwrap().to_le_bytes());
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self.0.update(value);
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}
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}
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impl<D: SecureDigest> Transcript for DigestTranscript<D> {
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type Challenge = Output<D>;
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fn new(name: &'static [u8]) -> Self {
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let mut res = DigestTranscript(D::new());
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res.append(DigestTranscriptMember::Name, name);
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res
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}
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fn domain_separate(&mut self, label: &[u8]) {
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self.append(DigestTranscriptMember::Domain, label);
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}
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fn append_message(&mut self, label: &'static [u8], message: &[u8]) {
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self.append(DigestTranscriptMember::Label, label);
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self.append(DigestTranscriptMember::Value, message);
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}
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fn challenge(&mut self, label: &'static [u8]) -> Self::Challenge {
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self.append(DigestTranscriptMember::Challenge, label);
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self.0.clone().finalize()
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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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#[cfg(feature = "recommended")]
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pub type RecommendedTranscript = DigestTranscript<blake2::Blake2b512>;
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