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113 lines
3.8 KiB
Rust
113 lines
3.8 KiB
Rust
#![cfg_attr(docsrs, feature(doc_cfg))]
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#![cfg_attr(docsrs, feature(doc_auto_cfg))]
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#![cfg_attr(not(feature = "std"), no_std)]
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use core::fmt::Debug;
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#[cfg(feature = "std")]
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use std::io::{self, Read};
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use rand_core::{RngCore, CryptoRng};
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use zeroize::Zeroize;
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use subtle::ConstantTimeEq;
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use digest::{core_api::BlockSizeUser, Digest, HashMarker};
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use transcript::SecureDigest;
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use group::{
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ff::{Field, PrimeField, PrimeFieldBits},
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Group, GroupOps,
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prime::PrimeGroup,
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};
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#[cfg(feature = "std")]
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use group::GroupEncoding;
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#[cfg(feature = "dalek")]
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mod dalek;
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#[cfg(feature = "ristretto")]
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pub use dalek::Ristretto;
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#[cfg(feature = "ed25519")]
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pub use dalek::Ed25519;
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#[cfg(feature = "kp256")]
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mod kp256;
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#[cfg(feature = "secp256k1")]
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pub use kp256::Secp256k1;
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#[cfg(feature = "p256")]
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pub use kp256::P256;
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#[cfg(feature = "ed448")]
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mod ed448;
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#[cfg(feature = "ed448")]
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pub use ed448::*;
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/// Unified trait defining a ciphersuite around an elliptic curve.
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pub trait Ciphersuite: Clone + Copy + PartialEq + Eq + Debug + Zeroize {
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/// Scalar field element type.
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// This is available via G::Scalar yet `C::G::Scalar` is ambiguous, forcing horrific accesses
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type F: PrimeField + PrimeFieldBits + Zeroize;
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/// Group element type.
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type G: Group<Scalar = Self::F> + GroupOps + PrimeGroup + Zeroize + ConstantTimeEq;
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/// Hash algorithm used with this curve.
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// Requires BlockSizeUser so it can be used within Hkdf which requies that.
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type H: Clone + BlockSizeUser + Digest + HashMarker + SecureDigest;
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/// ID for this curve.
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const ID: &'static [u8];
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/// Generator for the group.
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// While group does provide this in its API, privacy coins may want to use a custom basepoint
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fn generator() -> Self::G;
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/// Hash the provided domain-separation tag and message to a scalar. Ciphersuites MAY naively
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/// prefix the tag to the message, enabling transpotion between the two. Accordingly, this
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/// function should NOT be used in any scheme where one tag is a valid substring of another
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/// UNLESS the specific Ciphersuite is verified to handle the DST securely.
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///
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/// Verifying specific ciphersuites have secure tag handling is not recommended, due to it
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/// breaking the intended modularity of ciphersuites. Instead, component-specific tags with
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/// further purpose tags are recommended ("Schnorr-nonce", "Schnorr-chal").
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#[allow(non_snake_case)]
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fn hash_to_F(dst: &[u8], msg: &[u8]) -> Self::F;
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/// Generate a random non-zero scalar.
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#[allow(non_snake_case)]
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fn random_nonzero_F<R: RngCore + CryptoRng>(rng: &mut R) -> Self::F {
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let mut res;
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while {
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res = Self::F::random(&mut *rng);
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res.ct_eq(&Self::F::zero()).into()
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} {}
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res
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}
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/// Read a canonical scalar from something implementing std::io::Read.
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#[cfg(feature = "std")]
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#[allow(non_snake_case)]
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fn read_F<R: Read>(reader: &mut R) -> io::Result<Self::F> {
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let mut encoding = <Self::F as PrimeField>::Repr::default();
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reader.read_exact(encoding.as_mut())?;
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// ff mandates this is canonical
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let res = Option::<Self::F>::from(Self::F::from_repr(encoding))
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.ok_or_else(|| io::Error::new(io::ErrorKind::Other, "non-canonical scalar"));
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encoding.as_mut().zeroize();
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res
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}
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/// Read a canonical point from something implementing std::io::Read.
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#[cfg(feature = "std")]
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#[allow(non_snake_case)]
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fn read_G<R: Read>(reader: &mut R) -> io::Result<Self::G> {
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let mut encoding = <Self::G as GroupEncoding>::Repr::default();
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reader.read_exact(encoding.as_mut())?;
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let point = Option::<Self::G>::from(Self::G::from_bytes(&encoding))
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.ok_or_else(|| io::Error::new(io::ErrorKind::Other, "invalid point"))?;
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if point.to_bytes().as_ref() != encoding.as_ref() {
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Err(io::Error::new(io::ErrorKind::Other, "non-canonical point"))?;
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}
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Ok(point)
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}
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}
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