sn_curv 0.10.1

Curv contains an extremely simple interface to onboard new elliptic curves. Use this library for general purpose elliptic curve cryptography
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

/*
    This file is part of Curv library
    Copyright 2018 by Kzen Networks
    (https://github.com/KZen-networks/curv)
    License MIT: <https://github.com/KZen-networks/curv/blob/master/LICENSE>
*/

//! in ECDH Alice chooses at random a secret "a" and sends Bob public key A = aG
//! Bob chooses at random a secret "b" and sends to Alice B = bG.
//! Both parties can compute a joint secret: C = aB = bA = abG which cannot be computed by
//! a man in the middle attacker.

use serde::{Deserialize, Serialize};

use crate::elliptic::curves::{Curve, Point, Scalar};

#[derive(Clone, Debug, Serialize, Deserialize)]
#[serde(bound = "")]
pub struct EcKeyPair<E: Curve> {
    pub public_share: Point<E>,
    secret_share: Scalar<E>,
}

#[derive(Clone, Debug, Serialize, Deserialize)]
#[serde(bound = "")]
pub struct Party1FirstMessage<E: Curve> {
    pub public_share: Point<E>,
}
#[derive(Clone, Debug, Serialize, Deserialize)]
#[serde(bound = "")]
pub struct Party2FirstMessage<E: Curve> {
    pub public_share: Point<E>,
}

#[derive(Debug, Serialize, Deserialize)]
pub struct Party2SecondMessage {}

impl<E: Curve> Party1FirstMessage<E> {
    pub fn first() -> (Party1FirstMessage<E>, EcKeyPair<E>) {
        let base = Point::<E>::generator();

        let secret_share = Scalar::random();

        let public_share = base * &secret_share;

        let ec_key_pair = EcKeyPair {
            public_share: public_share.clone(),
            secret_share,
        };
        (Party1FirstMessage { public_share }, ec_key_pair)
    }

    pub fn first_with_fixed_secret_share(
        secret_share: Scalar<E>,
    ) -> (Party1FirstMessage<E>, EcKeyPair<E>) {
        let public_share = Point::generator() * secret_share.clone();

        let ec_key_pair = EcKeyPair {
            public_share: public_share.clone(),
            secret_share,
        };
        (Party1FirstMessage { public_share }, ec_key_pair)
    }
}

impl<E: Curve> Party2FirstMessage<E> {
    pub fn first() -> (Party2FirstMessage<E>, EcKeyPair<E>) {
        let base = Point::<E>::generator();
        let secret_share = Scalar::random();
        let public_share = base * &secret_share;
        let ec_key_pair = EcKeyPair {
            public_share: public_share.clone(),
            secret_share,
        };
        (Party2FirstMessage { public_share }, ec_key_pair)
    }

    pub fn first_with_fixed_secret_share(
        secret_share: Scalar<E>,
    ) -> (Party2FirstMessage<E>, EcKeyPair<E>) {
        let public_share = Point::generator() * &secret_share;
        let ec_key_pair = EcKeyPair {
            public_share: public_share.clone(),
            secret_share,
        };
        (Party2FirstMessage { public_share }, ec_key_pair)
    }
}

pub fn compute_pubkey<E: Curve>(
    local_share: &EcKeyPair<E>,
    other_share_public_share: &Point<E>,
) -> Point<E> {
    other_share_public_share * &local_share.secret_share
}

#[cfg(test)]
mod tests {
    use crate::cryptographic_primitives::twoparty::dh_key_exchange::*;
    use crate::elliptic::curves::Curve;
    use crate::test_for_all_curves;
    use crate::BigInt;
    use std::convert::TryFrom;

    test_for_all_curves!(test_dh_key_exchange_random_shares);
    fn test_dh_key_exchange_random_shares<E: Curve>() {
        let (kg_party_one_first_message, kg_ec_key_pair_party1) = Party1FirstMessage::<E>::first();
        let (kg_party_two_first_message, kg_ec_key_pair_party2) = Party2FirstMessage::<E>::first();

        assert_eq!(
            compute_pubkey(
                &kg_ec_key_pair_party2,
                &kg_party_one_first_message.public_share
            ),
            compute_pubkey(
                &kg_ec_key_pair_party1,
                &kg_party_two_first_message.public_share
            )
        );
    }

    test_for_all_curves!(test_dh_key_exchange_fixed_shares);
    fn test_dh_key_exchange_fixed_shares<E: Curve>() {
        let secret_party_1 = Scalar::try_from(&BigInt::from(1)).unwrap();
        let (kg_party_one_first_message, kg_ec_key_pair_party1) =
            Party1FirstMessage::<E>::first_with_fixed_secret_share(secret_party_1);
        let secret_party_2 = Scalar::try_from(&BigInt::from(2)).unwrap();

        let (kg_party_two_first_message, kg_ec_key_pair_party2) =
            Party2FirstMessage::first_with_fixed_secret_share(secret_party_2.clone());

        assert_eq!(
            compute_pubkey(
                &kg_ec_key_pair_party2,
                &kg_party_one_first_message.public_share
            ),
            compute_pubkey(
                &kg_ec_key_pair_party1,
                &kg_party_two_first_message.public_share
            )
        );
        assert_eq!(
            compute_pubkey(
                &kg_ec_key_pair_party2,
                &kg_party_one_first_message.public_share
            ),
            Point::generator() * secret_party_2
        );
    }
}