-
Notifications
You must be signed in to change notification settings - Fork 2
/
elgamal.rs
145 lines (125 loc) · 4.55 KB
/
elgamal.rs
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
use zei_algebra::ristretto::RistrettoPoint;
use zei_algebra::{
hash::{Hash, Hasher},
prelude::*,
};
#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
/// The ElGamal encryption key/public key.
pub struct ElGamalEncKey<G>(pub G);
#[derive(Debug, PartialEq, Eq, Serialize, Deserialize)]
/// The ElGamal decryption key/secret key.
pub struct ElGamalDecKey<S>(pub(crate) S);
#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
/// An ElGamal ciphertext.
pub struct ElGamalCiphertext<G> {
/// `e1` = `r * G`
pub e1: G,
/// `e2` = `m * G + r * pk`
pub e2: G,
}
impl Hash for ElGamalEncKey<RistrettoPoint> {
fn hash<H: Hasher>(&self, state: &mut H) {
self.0.to_compressed_bytes().as_slice().hash(state);
}
}
impl ZeiFromToBytes for ElGamalCiphertext<RistrettoPoint> {
fn zei_to_bytes(&self) -> Vec<u8> {
let mut v = vec![];
v.extend_from_slice(self.e1.to_compressed_bytes().as_slice());
v.extend_from_slice(self.e2.to_compressed_bytes().as_slice());
v
}
fn zei_from_bytes(bytes: &[u8]) -> Result<Self> {
let e1 = RistrettoPoint::from_compressed_bytes(&bytes[0..RistrettoPoint::COMPRESSED_LEN])
.c(d!(ZeiError::DeserializationError))?;
let e2 = RistrettoPoint::from_compressed_bytes(&bytes[RistrettoPoint::COMPRESSED_LEN..])
.c(d!(ZeiError::DeserializationError))?;
Ok(ElGamalCiphertext { e1, e2 })
}
}
/// Return an ElGamal key pair as `(sk, pk = sk * G)`
pub fn elgamal_key_gen<R: CryptoRng + RngCore, G: Group>(
prng: &mut R,
) -> (ElGamalDecKey<G::ScalarType>, ElGamalEncKey<G>) {
let base = G::get_base();
let secret_key = ElGamalDecKey(G::ScalarType::random(prng));
let public_key = ElGamalEncKey(base.mul(&secret_key.0));
(secret_key, public_key)
}
/// Return an ElGamal ciphertext pair as `(r * G, m * G + r * pk)`, where `G` is a base point on the curve
pub fn elgamal_encrypt<G: Group>(
m: &G::ScalarType,
r: &G::ScalarType,
pub_key: &ElGamalEncKey<G>,
) -> ElGamalCiphertext<G> {
let base = G::get_base();
let e1 = base.mul(r);
let e2 = base.mul(m).add(&(pub_key.0).mul(r));
ElGamalCiphertext::<G> { e1, e2 }
}
/// Verify that the ElGamal ciphertext encrypts m by checking `ctext.e2 - ctext.e1 * sk = m * G`
pub fn elgamal_verify<G: Group>(
m: &G::ScalarType,
ctext: &ElGamalCiphertext<G>,
sec_key: &ElGamalDecKey<G::ScalarType>,
) -> Result<()> {
let base = G::get_base();
if base.mul(m).add(&ctext.e1.mul(&sec_key.0)) == ctext.e2 {
Ok(())
} else {
Err(eg!(ZeiError::ElGamalVerificationError))
}
}
/// Perform a partial decryption for the ElGamal ciphertext that returns `m * G`
pub fn elgamal_partial_decrypt<G: Group>(
ctext: &ElGamalCiphertext<G>,
sec_key: &ElGamalDecKey<G::ScalarType>,
) -> G {
ctext.e2.sub(&ctext.e1.mul(&sec_key.0))
}
#[cfg(test)]
mod elgamal_test {
use ark_std::test_rng;
use zei_algebra::bls12_381::{BLSGt, BLSG1, BLSG2};
use zei_algebra::prelude::*;
use zei_algebra::ristretto::RistrettoPoint;
fn verification<G: Group>() {
let mut prng = test_rng();
let (secret_key, public_key) = super::elgamal_key_gen::<_, G>(&mut prng);
let m = G::ScalarType::from(100u32);
let r = G::ScalarType::random(&mut prng);
let ctext = super::elgamal_encrypt::<G>(&m, &r, &public_key);
pnk!(super::elgamal_verify::<G>(&m, &ctext, &secret_key));
let wrong_m = G::ScalarType::from(99u32);
let err = super::elgamal_verify(&wrong_m, &ctext, &secret_key)
.err()
.unwrap();
msg_eq!(ZeiError::ElGamalVerificationError, err);
}
fn decryption<G: Group>() {
let mut prng = test_rng();
let (secret_key, public_key) = super::elgamal_key_gen::<_, G>(&mut prng);
let mu32 = 100u32;
let m = G::ScalarType::from(mu32);
let r = G::ScalarType::random(&mut prng);
let ctext = super::elgamal_encrypt(&m, &r, &public_key);
pnk!(super::elgamal_verify(&m, &ctext, &secret_key));
let m = G::ScalarType::from(u64::MAX);
let ctext = super::elgamal_encrypt(&m, &r, &public_key);
pnk!(super::elgamal_verify(&m, &ctext, &secret_key));
}
#[test]
fn verify() {
verification::<RistrettoPoint>();
verification::<BLSG1>();
verification::<BLSG2>();
verification::<BLSGt>();
}
#[test]
fn decrypt() {
decryption::<RistrettoPoint>();
decryption::<BLSG1>();
decryption::<BLSG2>();
decryption::<BLSGt>();
}
}