slh_dsa/
signing_key.rs

use crate::address::{ForsTree, WotsHash};
use crate::signature_encoding::Signature;
use crate::util::split_digest;
use crate::verifying_key::VerifyingKey;
use crate::{ParameterSet, PkSeed, Sha2L1, Sha2L35, Shake, VerifyingKeyLen};
use ::signature::{Error, KeypairRef, RandomizedSigner, Signer};
use hybrid_array::{Array, ArraySize};
use typenum::{Unsigned, U, U16, U24, U32};

// NewTypes for ensuring hash argument order correctness
#[derive(Clone, PartialEq, Eq, Debug)]
pub(crate) struct SkSeed<N: ArraySize>(pub(crate) Array<u8, N>);
impl<N: ArraySize> AsRef<[u8]> for SkSeed<N> {
    fn as_ref(&self) -> &[u8] {
        self.0.as_ref()
    }
}
impl<N: ArraySize> From<&[u8]> for SkSeed<N> {
    fn from(slice: &[u8]) -> Self {
        #[allow(deprecated)]
        Self(Array::clone_from_slice(slice))
    }
}
impl<N: ArraySize> SkSeed<N> {
    pub(crate) fn new(rng: &mut impl rand_core::CryptoRngCore) -> Self {
        let mut bytes = Array::<u8, N>::default();
        rng.fill_bytes(bytes.as_mut_slice());
        Self(bytes)
    }
}

#[derive(Clone, PartialEq, Eq, Debug)]
pub(crate) struct SkPrf<N: ArraySize>(pub(crate) Array<u8, N>);
impl<N: ArraySize> AsRef<[u8]> for SkPrf<N> {
    fn as_ref(&self) -> &[u8] {
        self.0.as_ref()
    }
}
impl<N: ArraySize> From<&[u8]> for SkPrf<N> {
    fn from(slice: &[u8]) -> Self {
        #[allow(deprecated)]
        Self(Array::clone_from_slice(slice))
    }
}
impl<N: ArraySize> SkPrf<N> {
    pub(crate) fn new(rng: &mut impl rand_core::CryptoRngCore) -> Self {
        let mut bytes = Array::<u8, N>::default();
        rng.fill_bytes(bytes.as_mut_slice());
        Self(bytes)
    }
}

/// A `SigningKey` allows signing messages with a fixed parameter set
#[derive(Clone, PartialEq, Eq, Debug)]
pub struct SigningKey<P: ParameterSet> {
    pub(crate) sk_seed: SkSeed<P::N>,
    pub(crate) sk_prf: SkPrf<P::N>,
    pub(crate) verifying_key: VerifyingKey<P>,
}

/// A trait specifying the length of a serialized signing key for a given parameter set
pub trait SigningKeyLen: VerifyingKeyLen {
    /// The length of the serialized signing key in bytes
    type SkLen: ArraySize;
}

impl<P: ParameterSet> SigningKey<P> {
    /// Create a new `SigningKey` from a cryptographic random number generator
    pub fn new(rng: &mut impl rand_core::CryptoRngCore) -> Self {
        let sk_seed = SkSeed::new(rng);
        let sk_prf = SkPrf::new(rng);
        let pk_seed = PkSeed::new(rng);
        Self::from_seed(sk_seed, sk_prf, pk_seed)
    }

    fn from_seed(sk_seed: SkSeed<P::N>, sk_prf: SkPrf<P::N>, pk_seed: PkSeed<P::N>) -> Self {
        let mut adrs = WotsHash::default();
        adrs.layer_adrs.set(P::D::U32 - 1);

        let pk_root = P::xmss_node(&sk_seed, 0, P::HPrime::U32, &pk_seed, &adrs);
        let verifying_key = VerifyingKey { pk_seed, pk_root };
        SigningKey {
            sk_seed,
            sk_prf,
            verifying_key,
        }
    }

    #[doc(hidden)]
    #[allow(clippy::must_use_candidate)]
    /// Construct a new SigningKey from pre-chosen seeds.
    /// Implements [slh_keygen_internal] as defined in FIPS-205.
    /// Published for KAT validation purposes but not intended for general use.
    pub fn slh_keygen_internal(sk_seed: &[u8], sk_prf: &[u8], pk_seed: &[u8]) -> Self {
        let sk_seed = SkSeed::from(sk_seed);
        let sk_prf = SkPrf::from(sk_prf);
        let pk_seed = PkSeed::from(pk_seed);
        Self::from_seed(sk_seed, sk_prf, pk_seed)
    }

    #[doc(hidden)]
    /// Sign a message with a pre-chosen randomizer.
    /// Implements [slh_sign_internal] as defined in FIPS-205.
    /// Published for KAT validation purposes but not intended for general use.
    /// opt_rand must be a P::N length slice, panics otherwise.
    pub fn slh_sign_internal(&self, msg: &[u8], opt_rand: Option<&[u8]>) -> Signature<P> {
        let rand = opt_rand
            .unwrap_or(&self.verifying_key.pk_seed.0)
            .try_into()
            .unwrap();

        let sk_seed = &self.sk_seed;
        let pk_seed = &self.verifying_key.pk_seed;

        let randomizer = P::prf_msg(&self.sk_prf, rand, msg);

        let digest = P::h_msg(&randomizer, pk_seed, &self.verifying_key.pk_root, msg);
        let (md, idx_tree, idx_leaf) = split_digest::<P>(&digest);
        let adrs = ForsTree::new(idx_tree, idx_leaf);
        let fors_sig = P::fors_sign(md, sk_seed, pk_seed, &adrs);

        let fors_pk = P::fors_pk_from_sig(&fors_sig, md, pk_seed, &adrs);
        let ht_sig = P::ht_sign(&fors_pk, sk_seed, pk_seed, idx_tree, idx_leaf);

        Signature {
            randomizer,
            fors_sig,
            ht_sig,
        }
    }

    /// Implements [slh-sign] as defined in FIPS-205, using a context string.
    /// Context strings must be 255 bytes or less.
    /// # Errors
    /// Returns an error if the context string is too long.
    pub fn try_sign_with_context(
        &self,
        msg: &[u8],
        ctx: &[u8],
        opt_rand: Option<&[u8]>,
    ) -> Result<Signature<P>, Error> {
        let ctx_len = u8::try_from(ctx.len()).map_err(|_| Error::new())?;
        let ctx_len_bytes = ctx_len.to_be_bytes();

        // TODO - figure out what to do about this allocation. Maybe pass a chained iterator to slh_sign_internal?
        let ctx_msg = [&[0], &ctx_len_bytes, ctx, msg].concat();
        Ok(self.slh_sign_internal(&ctx_msg, opt_rand))
    }

    /// Serialize the signing key to a new stack-allocated array
    ///
    /// This clones the underlying fields
    pub fn to_bytes(&self) -> Array<u8, P::SkLen> {
        let mut bytes = Array::<u8, P::SkLen>::default();
        bytes[..P::N::USIZE].copy_from_slice(&self.sk_seed.0);
        bytes[P::N::USIZE..2 * P::N::USIZE].copy_from_slice(&self.sk_prf.0);
        bytes[2 * P::N::USIZE..].copy_from_slice(&self.verifying_key.to_bytes());
        bytes
    }

    /// Serialize the signing key to a new heap-allocated vector
    #[cfg(feature = "alloc")]
    pub fn to_vec(&self) -> Vec<u8>
    where
        P: VerifyingKeyLen,
    {
        self.to_bytes().to_vec()
    }
}

impl<P: ParameterSet> TryFrom<&[u8]> for SigningKey<P> {
    type Error = Error;

    fn try_from(bytes: &[u8]) -> Result<Self, Self::Error> {
        if bytes.len() != P::SkLen::USIZE {
            return Err(Error::new());
        }

        let (sk_seed_bytes, rest) = bytes.split_at(P::N::USIZE);
        let (sk_prf_bytes, verifying_key_bytes) = rest.split_at(P::N::USIZE);
        let verifying_key = VerifyingKey::try_from(verifying_key_bytes)?;

        Ok(SigningKey {
            sk_seed: SkSeed::from(sk_seed_bytes),
            sk_prf: SkPrf::from(sk_prf_bytes),
            verifying_key,
        })
    }
}

impl<P: ParameterSet> Signer<Signature<P>> for SigningKey<P> {
    fn try_sign(&self, msg: &[u8]) -> Result<Signature<P>, Error> {
        self.try_sign_with_context(msg, &[], None)
    }
}

impl<P: ParameterSet> RandomizedSigner<Signature<P>> for SigningKey<P> {
    fn try_sign_with_rng(
        &self,
        rng: &mut impl signature::rand_core::CryptoRngCore,
        msg: &[u8],
    ) -> Result<Signature<P>, signature::Error> {
        let mut randomizer = Array::<u8, P::N>::default();
        rng.fill_bytes(randomizer.as_mut_slice());
        self.try_sign_with_context(msg, &[], Some(&randomizer))
    }
}

impl<P: ParameterSet> AsRef<VerifyingKey<P>> for SigningKey<P> {
    fn as_ref(&self) -> &VerifyingKey<P> {
        &self.verifying_key
    }
}

impl<P: ParameterSet> KeypairRef for SigningKey<P> {
    type VerifyingKey = VerifyingKey<P>;
}

impl<M> SigningKeyLen for Sha2L1<U16, M> {
    type SkLen = U<{ 4 * 16 }>;
}

impl<M> SigningKeyLen for Sha2L35<U24, M> {
    type SkLen = U<{ 4 * 24 }>;
}
impl<M> SigningKeyLen for Sha2L35<U32, M> {
    type SkLen = U<{ 4 * 32 }>;
}

impl<M> SigningKeyLen for Shake<U16, M> {
    type SkLen = U<{ 4 * 16 }>;
}
impl<M> SigningKeyLen for Shake<U24, M> {
    type SkLen = U<{ 4 * 24 }>;
}
impl<M> SigningKeyLen for Shake<U32, M> {
    type SkLen = U<{ 4 * 32 }>;
}

#[cfg(test)]
mod tests {
    use crate::{util::macros::test_parameter_sets, ParameterSet, SigningKey};

    fn test_serialize_deserialize<P: ParameterSet>() {
        let mut rng: rand::prelude::ThreadRng = rand::thread_rng();
        let sk = SigningKey::<P>::new(&mut rng);
        let bytes = sk.to_bytes();
        let sk2 = SigningKey::<P>::try_from(bytes.as_slice()).unwrap();
        assert_eq!(sk, sk2);
    }
    test_parameter_sets!(test_serialize_deserialize);

    #[cfg(feature = "alloc")]
    fn test_serialize_deserialize_vec<P: ParameterSet>() {
        let mut rng: rand::prelude::ThreadRng = rand::thread_rng();
        let sk = SigningKey::<P>::new(&mut rng);
        let vec = sk.to_vec();
        let sk2 = SigningKey::<P>::try_from(vec.as_slice()).unwrap();
        assert_eq!(sk, sk2);
    }
    #[cfg(feature = "alloc")]
    test_parameter_sets!(test_serialize_deserialize_vec);

    #[test]
    fn test_deserialize_fail_on_incorrect_length() {
        let mut rng: rand::prelude::ThreadRng = rand::thread_rng();
        let sk = SigningKey::<Shake128f>::new(&mut rng);
        let bytes = sk.to_bytes();
        let incorrect_bytes = &bytes[..bytes.len() - 1];
        assert!(SigningKey::<Shake128f>::try_from(incorrect_bytes).is_err());
    }
}
slh_dsa/signing_key.rs

slh_dsa/
signing_key.rs
