mithril_stm/bls_multi_signature/
verification_key.rs

1use std::{
2    cmp::Ordering,
3    fmt::{Display, Formatter},
4    hash::{Hash, Hasher},
5    iter::Sum,
6};
7
8use blst::{
9    BLST_ERROR,
10    min_sig::{AggregatePublicKey, PublicKey as BlstVk},
11};
12use serde::{Deserialize, Serialize};
13
14use crate::bls_multi_signature::{
15    BlsProofOfPossession, BlsSigningKey, POP, helper::unsafe_helpers::verify_pairing,
16};
17use crate::error::{MultiSignatureError, blst_err_to_mithril};
18
19/// MultiSig verification key, which is a wrapper over the BlstVk (element in G2)
20/// from the blst library.
21#[derive(Debug, Clone, Copy, Default)]
22pub struct BlsVerificationKey(pub BlstVk);
23
24impl BlsVerificationKey {
25    /// Convert an `VerificationKey` to its compressed byte representation.
26    pub fn to_bytes(self) -> [u8; 96] {
27        self.0.to_bytes()
28    }
29
30    /// Convert a compressed byte string into a `VerificationKey`.
31    ///
32    /// # Error
33    /// This function fails if the bytes do not represent a compressed point of the prime
34    /// order subgroup of the curve Bls12-381.
35    pub fn from_bytes(bytes: &[u8]) -> Result<Self, MultiSignatureError> {
36        let bytes = bytes.get(..96).ok_or(MultiSignatureError::SerializationError)?;
37        match BlstVk::key_validate(bytes) {
38            Ok(vk) => Ok(Self(vk)),
39            Err(e) => Err(blst_err_to_mithril(e, None, None)
40                .expect_err("If deserialization is not successful, blst returns and error different to SUCCESS."))
41        }
42    }
43
44    /// Compare two `VerificationKey`. Used for PartialOrd impl, used to order signatures. The comparison
45    /// function can be anything, as long as it is consistent.
46    fn compare_verification_keys(&self, other: &BlsVerificationKey) -> Ordering {
47        let self_bytes = self.to_bytes();
48        let other_bytes = other.to_bytes();
49        let mut result = Ordering::Equal;
50
51        for (i, j) in self_bytes.iter().zip(other_bytes.iter()) {
52            result = i.cmp(j);
53            if result != Ordering::Equal {
54                return result;
55            }
56        }
57
58        result
59    }
60
61    pub(crate) fn to_blst_verification_key(self) -> BlstVk {
62        self.0
63    }
64}
65
66impl Display for BlsVerificationKey {
67    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
68        write!(f, "{:?}", self.to_bytes())
69    }
70}
71
72impl Hash for BlsVerificationKey {
73    fn hash<H: Hasher>(&self, state: &mut H) {
74        Hash::hash_slice(&self.to_bytes(), state)
75    }
76}
77
78impl PartialEq for BlsVerificationKey {
79    fn eq(&self, other: &Self) -> bool {
80        self.0 == other.0
81    }
82}
83
84impl Eq for BlsVerificationKey {}
85
86impl PartialOrd for BlsVerificationKey {
87    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
88        Some(std::cmp::Ord::cmp(self, other))
89    }
90}
91
92impl Ord for BlsVerificationKey {
93    fn cmp(&self, other: &Self) -> Ordering {
94        self.compare_verification_keys(other)
95    }
96}
97
98impl<'a> Sum<&'a Self> for BlsVerificationKey {
99    fn sum<I>(iter: I) -> Self
100    where
101        I: Iterator<Item = &'a Self>,
102    {
103        let keys: Vec<&BlstVk> = iter.map(|x| &x.0).collect();
104
105        assert!(!keys.is_empty(), "One cannot add an empty vector");
106        let aggregate_key = AggregatePublicKey::aggregate(&keys, false)
107            .expect("An MspMvk is always a valid key. This function only fails if keys is empty or if the keys are invalid, none of which can happen.")
108            .to_public_key();
109
110        Self(aggregate_key)
111    }
112}
113
114impl From<&BlsSigningKey> for BlsVerificationKey {
115    /// Convert a secret key into an `MspMvk`. This is performed by computing
116    /// `MspMvk = g2 * sk`, where `g2` is the generator in G2. We can use the
117    /// blst built-in function `sk_to_pk`.
118    fn from(sk: &BlsSigningKey) -> Self {
119        BlsVerificationKey(sk.to_blst_secret_key().sk_to_pk())
120    }
121}
122
123/// MultiSig public key, contains the verification key and the proof of possession.
124#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
125pub struct BlsVerificationKeyProofOfPossession {
126    /// The verification key.
127    pub vk: BlsVerificationKey,
128    /// Proof of Possession.
129    pub pop: BlsProofOfPossession,
130}
131
132impl BlsVerificationKeyProofOfPossession {
133    /// if `e(k1,g2) = e(H_G1("PoP" || mvk),mvk)` and `e(g1,mvk) = e(k2,g2)`
134    /// are both true, return 1. The first part is a signature verification
135    /// of message "PoP", while the second we need to compute the pairing
136    /// manually.
137    // If we are really looking for performance improvements, we can combine the
138    // two final exponentiations (for verifying k1 and k2) into a single one.
139    pub(crate) fn verify_proof_of_possession(&self) -> Result<(), MultiSignatureError> {
140        match self.vk.to_blst_verification_key().validate() {
141            Ok(_) => {
142                let result = verify_pairing(&self.vk, &self.pop);
143                if !(self.pop.get_k1().verify(
144                    false,
145                    POP,
146                    &[],
147                    &[],
148                    &self.vk.to_blst_verification_key(),
149                    false,
150                ) == BLST_ERROR::BLST_SUCCESS
151                    && result)
152                {
153                    return Err(MultiSignatureError::KeyInvalid(Box::new(*self)));
154                }
155                Ok(())
156            }
157            Err(e) => blst_err_to_mithril(e, None, Some(self.vk)),
158        }
159    }
160
161    /// if `e(k1,g2) = e(H_G1("PoP" || mvk),mvk)` and `e(g1,mvk) = e(k2,g2)`
162    /// are both true, return 1. The first part is a signature verification
163    /// of message "PoP", while the second we need to compute the pairing
164    /// manually.
165    // If we are really looking for performance improvements, we can combine the
166    // two final exponentiations (for verifying k1 and k2) into a single one.
167    #[deprecated(
168        since = "0.5.0",
169        note = "The verification of the proof of possession is not part of the public API any more"
170    )]
171    pub fn check(&self) -> Result<(), MultiSignatureError> {
172        Self::verify_proof_of_possession(self)
173    }
174
175    /// Convert to a 144 byte string.
176    ///
177    /// # Layout
178    /// The layout of a `PublicKeyPoP` encoding is
179    /// * Public key
180    /// * Proof of Possession
181    pub fn to_bytes(self) -> [u8; 192] {
182        let mut vkpop_bytes = [0u8; 192];
183        vkpop_bytes[..96].copy_from_slice(&self.vk.to_bytes());
184        vkpop_bytes[96..].copy_from_slice(&self.pop.to_bytes());
185        vkpop_bytes
186    }
187
188    /// Deserialize a byte string to a `BlsVerificationKeyProofOfPossession`.
189    pub fn from_bytes(bytes: &[u8]) -> Result<Self, MultiSignatureError> {
190        let mvk = BlsVerificationKey::from_bytes(
191            bytes.get(..96).ok_or(MultiSignatureError::SerializationError)?,
192        )?;
193
194        let pop = BlsProofOfPossession::from_bytes(
195            bytes.get(96..).ok_or(MultiSignatureError::SerializationError)?,
196        )?;
197
198        Ok(Self { vk: mvk, pop })
199    }
200}
201
202impl From<&BlsSigningKey> for BlsVerificationKeyProofOfPossession {
203    /// Convert a secret key into a `BlsVerificationKeyProofOfPossession` by simply converting to a
204    /// `MspMvk` and `MspPoP`.
205    fn from(sk: &BlsSigningKey) -> Self {
206        Self {
207            vk: sk.into(),
208            pop: sk.into(),
209        }
210    }
211}
212
213#[cfg(test)]
214mod tests {
215    use super::*;
216
217    mod golden {
218
219        use rand_chacha::ChaCha20Rng;
220        use rand_core::SeedableRng;
221
222        use super::*;
223
224        const GOLDEN_JSON: &str = r#"
225            {
226                "vk": [143, 161, 255, 48, 78, 57, 204, 220, 25, 221, 164, 252, 248, 14, 56, 126, 186, 135, 228, 188, 145, 181, 52, 200, 97, 99, 213, 46, 0, 199, 193, 89, 187, 88, 29, 135, 173, 244, 86, 36, 83, 54, 67, 164, 6, 137, 94, 72, 6, 105, 128, 128, 93, 48, 176, 11, 4, 246, 138, 48, 180, 133, 90, 142, 192, 24, 193, 111, 142, 31, 76, 111, 110, 234, 153, 90, 208, 192, 31, 124, 95, 102, 49, 158, 99, 52, 220, 165, 94, 251, 68, 69, 121, 16, 224, 194],
227                "pop": [168, 50, 233, 193, 15, 136, 65, 72, 123, 148, 129, 176, 38, 198, 209, 47, 28, 204, 176, 144, 57, 251, 42, 28, 66, 76, 89, 97, 158, 63, 54, 198, 194, 176, 135, 221, 14, 185, 197, 225, 202, 98, 243, 74, 233, 225, 143, 151, 147, 177, 170, 117, 66, 165, 66, 62, 33, 216, 232, 75, 68, 114, 195, 22, 100, 65, 44, 198, 4, 166, 102, 233, 253, 240, 59, 175, 60, 117, 142, 114, 140, 122, 17, 87, 110, 187, 1, 17, 10, 195, 154, 13, 249, 86, 54, 226]
228            }
229        "#;
230
231        fn golden_value() -> BlsVerificationKeyProofOfPossession {
232            let mut rng = ChaCha20Rng::from_seed([0u8; 32]);
233            let sk = BlsSigningKey::generate(&mut rng);
234            BlsVerificationKeyProofOfPossession {
235                vk: BlsVerificationKey::from(&sk),
236                pop: BlsProofOfPossession::from(&sk),
237            }
238        }
239
240        #[test]
241        fn golden_conversions() {
242            let value = serde_json::from_str(GOLDEN_JSON)
243                .expect("This JSON deserialization should not fail");
244            assert_eq!(golden_value(), value);
245
246            let serialized =
247                serde_json::to_string(&value).expect("This JSON serialization should not fail");
248            let golden_serialized = serde_json::to_string(&golden_value())
249                .expect("This JSON serialization should not fail");
250            assert_eq!(golden_serialized, serialized);
251        }
252    }
253}
mithril_stm/bls_multi_signature/verification_key.rs

mithril_stm/bls_multi_signature/
verification_key.rs
