pqc-sig 0.5.1

Post-quantum digital signatures: ML-DSA (FIPS 204), SLH-DSA (FIPS 205), FN-DSA (FIPS 206) — standalone WASM-compatible
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213

//! SLH-DSA-SHA2-128s (NIST FIPS 205, Security Level 1, small signatures)
//!
//! Parameter sizes:
//! - Public key:   32 bytes  (N=16, VkLen=2*N=32)
//! - Secret key:   64 bytes  (N=16, SkLen=4*N=64)
//! - Signature:  7856 bytes

extern crate alloc;
use alloc::format;

use slh_dsa::{SigningKey, VerifyingKey, Sha2_128s};
use slh_dsa::signature::{Keypair, Signer, Verifier};
use rand_core::{CryptoRng, RngCore};

use crate::ctx::check_ctx;
use crate::error::{SigError, SigResult};
use crate::prehash::{check_prehash, frame_prehash, PreHash};
use crate::types::{SigAlgorithm, SigPublicKey, SigSecretKey, Signature};

/// SLH-DSA-SHA2-128s keypair (NIST FIPS 205, Security Level 1, small signatures).
pub struct SlhDsaSha2_128sKeypair {
    signing_key: SigningKey<Sha2_128s>,
}

impl SlhDsaSha2_128sKeypair {
    /// Security strength in bits (FIPS 205 §10.2.2 pre-hash collision-strength floor).
    pub const SECURITY_STRENGTH_BITS: u32 = 128;

    /// Generate a new keypair using the provided RNG.
    pub fn generate<R: CryptoRng + RngCore>(rng: &mut R) -> SigResult<Self> {
        // N=16 for SHA2-128 parameter sets
        let mut sk_seed = [0u8; 16];
        let mut sk_prf  = [0u8; 16];
        let mut pk_seed = [0u8; 16];
        rng.fill_bytes(&mut sk_seed);
        rng.fill_bytes(&mut sk_prf);
        rng.fill_bytes(&mut pk_seed);
        let signing_key = SigningKey::<Sha2_128s>::slh_keygen_internal(&sk_seed, &sk_prf, &pk_seed);
        Ok(Self { signing_key })
    }

    /// Returns the public (verifying) key.
    pub fn public_key(&self) -> SigPublicKey {
        SigPublicKey::new(SigAlgorithm::SlhDsaSha2_128s, self.signing_key.verifying_key().to_bytes().to_vec())
    }

    /// Returns the secret (signing) key.
    pub fn secret_key(&self) -> SigSecretKey {
        SigSecretKey::new(SigAlgorithm::SlhDsaSha2_128s, self.signing_key.to_bytes().to_vec())
    }

    /// Sign a message (randomized signing — uses RNG to produce non-deterministic signatures).
    ///
    /// Each call with the same message produces a different signature (randomized per FIPS 205).
    pub fn sign<R: CryptoRng + RngCore>(&self, rng: &mut R, message: &[u8]) -> SigResult<Signature> {
        // N=16 for SHA2-128 parameter sets. Bridge rand_core 0.6 → try_sign_with_context opt_rand.
        // Use try_sign_with_context (not slh_sign_internal) to include the FIPS 205 domain separator.
        let mut opt_rand = [0u8; 16];
        rng.fill_bytes(&mut opt_rand);
        let sig = self.signing_key.try_sign_with_context(message, &[], Some(&opt_rand))
            .map_err(|e| SigError::Signing(format!("{:?}", e)))?;
        Ok(Signature::new(SigAlgorithm::SlhDsaSha2_128s, sig.to_bytes().to_vec()))
    }

    /// Sign a message deterministically (same message always produces same signature).
    pub fn sign_deterministic(&self, message: &[u8]) -> SigResult<Signature> {
        let sig = self.signing_key.try_sign(message)
            .map_err(|e| SigError::Signing(format!("{:?}", e)))?;
        Ok(Signature::new(SigAlgorithm::SlhDsaSha2_128s, sig.to_bytes().to_vec()))
    }

    /// Verify a signature over a message using the given public key.
    pub fn verify(public_key: &SigPublicKey, message: &[u8], signature: &Signature) -> SigResult<()> {
        if public_key.algorithm != SigAlgorithm::SlhDsaSha2_128s {
            return Err(SigError::InvalidPublicKey(format!("expected SLH-DSA-SHA2-128s key, got {:?}", public_key.algorithm)));
        }
        if signature.algorithm != SigAlgorithm::SlhDsaSha2_128s {
            return Err(SigError::InvalidSignature(format!("expected SLH-DSA-SHA2-128s signature, got {:?}", signature.algorithm)));
        }
        let vk = VerifyingKey::<Sha2_128s>::try_from(public_key.bytes.as_slice())
            .map_err(|e| SigError::InvalidPublicKey(format!("{:?}", e)))?;
        let sig = slh_dsa::Signature::<Sha2_128s>::try_from(signature.bytes.as_slice())
            .map_err(|e| SigError::InvalidSignature(format!("{:?}", e)))?;
        vk.verify(message, &sig).map_err(|_| SigError::VerificationFailed)
    }

    /// Sign a message with a domain-separation context string (FIPS 205 §10.2), randomized.
    ///
    /// `ctx` binds the signature to a specific application or protocol — see the
    /// crate-level "Domain separation" docs. Must be at most
    /// [`MAX_CONTEXT_LEN`](crate::MAX_CONTEXT_LEN) bytes.
    pub fn sign_ctx<R: CryptoRng + RngCore>(&self, rng: &mut R, ctx: &[u8], message: &[u8]) -> SigResult<Signature> {
        check_ctx(ctx)?;
        // N=16 for SHA2-128 parameter sets.
        let mut opt_rand = [0u8; 16];
        rng.fill_bytes(&mut opt_rand);
        let sig = self.signing_key.try_sign_with_context(message, ctx, Some(&opt_rand))
            .map_err(|e| SigError::Signing(format!("{:?}", e)))?;
        Ok(Signature::new(SigAlgorithm::SlhDsaSha2_128s, sig.to_bytes().to_vec()))
    }

    /// Sign a message deterministically with a domain-separation context string.
    ///
    /// See [`Self::sign_ctx`] for details on `ctx`. An empty `ctx` (`&[]`) produces a
    /// signature byte-identical to [`Self::sign_deterministic`].
    pub fn sign_ctx_deterministic(&self, ctx: &[u8], message: &[u8]) -> SigResult<Signature> {
        check_ctx(ctx)?;
        let sig = self.signing_key.try_sign_with_context(message, ctx, None)
            .map_err(|e| SigError::Signing(format!("{:?}", e)))?;
        Ok(Signature::new(SigAlgorithm::SlhDsaSha2_128s, sig.to_bytes().to_vec()))
    }

    /// Verify a signature made with [`Self::sign_ctx`]/[`Self::sign_ctx_deterministic`].
    ///
    /// `ctx` must match exactly what was used to sign. An empty `ctx` (`&[]`) verifies
    /// signatures made by [`Self::sign`]/[`Self::sign_deterministic`] (and vice versa).
    pub fn verify_ctx(public_key: &SigPublicKey, ctx: &[u8], message: &[u8], signature: &Signature) -> SigResult<()> {
        check_ctx(ctx)?;
        if public_key.algorithm != SigAlgorithm::SlhDsaSha2_128s {
            return Err(SigError::InvalidPublicKey(format!("expected SLH-DSA-SHA2-128s key, got {:?}", public_key.algorithm)));
        }
        if signature.algorithm != SigAlgorithm::SlhDsaSha2_128s {
            return Err(SigError::InvalidSignature(format!("expected SLH-DSA-SHA2-128s signature, got {:?}", signature.algorithm)));
        }
        let vk = VerifyingKey::<Sha2_128s>::try_from(public_key.bytes.as_slice())
            .map_err(|e| SigError::InvalidPublicKey(format!("{:?}", e)))?;
        let sig = slh_dsa::Signature::<Sha2_128s>::try_from(signature.bytes.as_slice())
            .map_err(|e| SigError::InvalidSignature(format!("{:?}", e)))?;
        vk.try_verify_with_context(message, ctx, &sig).map_err(|_| SigError::VerificationFailed)
    }

    /// Sign a pre-computed digest using the `HashSLH-DSA` construction (FIPS 205
    /// §10.2.2, Algorithm 23), randomized.
    ///
    /// `digest` is the output of hashing the actual message with `hash` — this crate
    /// never hashes on the caller's behalf (see the crate-level "Pre-hash signing"
    /// docs). `hash.collision_strength_bits()` must be at least
    /// [`Self::SECURITY_STRENGTH_BITS`] or this returns [`SigError::PreHashTooWeak`];
    /// `digest.len()` must equal `hash.digest_len()` or this returns
    /// [`SigError::InvalidDigestLength`]. `ctx` follows the same rules as
    /// [`Self::sign_ctx`].
    ///
    /// This builds `M' = 0x01 ‖ len(ctx) ‖ ctx ‖ OID(hash) ‖ digest` and signs it via
    /// the upstream `slh-dsa` crate's `slh_sign_internal` — the literal FIPS 205
    /// `HashSLH-DSA.Sign` construction, byte-for-byte interoperable with any
    /// conformant verifier.
    pub fn sign_prehash<R: CryptoRng + RngCore>(
        &self,
        rng: &mut R,
        ctx: &[u8],
        hash: PreHash,
        digest: &[u8],
    ) -> SigResult<Signature> {
        check_ctx(ctx)?;
        check_prehash(hash, digest, Self::SECURITY_STRENGTH_BITS, "SLH-DSA-SHA2-128s")?;
        let m_prime = frame_prehash(ctx, hash, digest);
        // N=16 for SHA2-128 parameter sets.
        let mut opt_rand = [0u8; 16];
        rng.fill_bytes(&mut opt_rand);
        let sig = self.signing_key.slh_sign_internal(&[m_prime.as_slice()], Some(&opt_rand));
        Ok(Signature::new(SigAlgorithm::SlhDsaSha2_128s, sig.to_bytes().to_vec()))
    }

    /// Sign a pre-computed digest deterministically using the `HashSLH-DSA`
    /// construction. See [`Self::sign_prehash`] for the framing and validation rules.
    pub fn sign_prehash_deterministic(
        &self,
        ctx: &[u8],
        hash: PreHash,
        digest: &[u8],
    ) -> SigResult<Signature> {
        check_ctx(ctx)?;
        check_prehash(hash, digest, Self::SECURITY_STRENGTH_BITS, "SLH-DSA-SHA2-128s")?;
        let m_prime = frame_prehash(ctx, hash, digest);
        let sig = self.signing_key.slh_sign_internal(&[m_prime.as_slice()], None);
        Ok(Signature::new(SigAlgorithm::SlhDsaSha2_128s, sig.to_bytes().to_vec()))
    }

    /// Verify a signature made with [`Self::sign_prehash`]/[`Self::sign_prehash_deterministic`].
    ///
    /// A pre-hash signature does **not** verify via [`Self::verify`]/[`Self::verify_ctx`]
    /// (and vice versa) — the `0x01` domain byte in `M'` structurally separates
    /// `HashSLH-DSA` from pure-mode SLH-DSA, per FIPS 205 §10.2.2.
    pub fn verify_prehash(
        public_key: &SigPublicKey,
        ctx: &[u8],
        hash: PreHash,
        digest: &[u8],
        signature: &Signature,
    ) -> SigResult<()> {
        check_ctx(ctx)?;
        check_prehash(hash, digest, Self::SECURITY_STRENGTH_BITS, "SLH-DSA-SHA2-128s")?;
        if public_key.algorithm != SigAlgorithm::SlhDsaSha2_128s {
            return Err(SigError::InvalidPublicKey(format!("expected SLH-DSA-SHA2-128s key, got {:?}", public_key.algorithm)));
        }
        if signature.algorithm != SigAlgorithm::SlhDsaSha2_128s {
            return Err(SigError::InvalidSignature(format!("expected SLH-DSA-SHA2-128s signature, got {:?}", signature.algorithm)));
        }
        let vk = VerifyingKey::<Sha2_128s>::try_from(public_key.bytes.as_slice())
            .map_err(|e| SigError::InvalidPublicKey(format!("{:?}", e)))?;
        let sig = slh_dsa::Signature::<Sha2_128s>::try_from(signature.bytes.as_slice())
            .map_err(|e| SigError::InvalidSignature(format!("{:?}", e)))?;
        let m_prime = frame_prehash(ctx, hash, digest);
        vk.slh_verify_internal(&[m_prime.as_slice()], &sig).map_err(|_| SigError::VerificationFailed)
    }

    /// Restore a keypair from raw secret key bytes.
    pub fn from_secret_key_bytes(bytes: &[u8]) -> SigResult<Self> {
        let signing_key = SigningKey::<Sha2_128s>::try_from(bytes)
            .map_err(|e| SigError::InvalidSecretKey(format!("{:?}", e)))?;
        Ok(Self { signing_key })
    }
}