rac 1.3.4

Traits and types to work with elliptic curve
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

use generic_array::GenericArray;
use digest::{FixedOutput, Update};
use core::marker::PhantomData;
use crate::{
    line::{Array, LineValid},
    concat::Concat,
    elliptic::{Scalar, Curve},
};

pub trait Signature
where
    Self: LineValid,
{
    type Scalar: Scalar;

    type Curve: Curve<Scalar = Self::Scalar>;

    fn sign<M>(secret_key: &Self::Scalar, message: &M, seed: &Self::Scalar) -> Result<Self, ()>
    where
        M: AsRef<[u8]>;

    fn verify<M>(&self, public_key: &Self::Curve, message: &M) -> Result<(), ()>
    where
        M: AsRef<[u8]>;
}

#[derive(Debug, Clone)]
pub struct Schnorr<C, D>
where
    C: Curve,
    D: Default + Update + FixedOutput<OutputSize = <C::Scalar as LineValid>::Length>,
    Concat<Array<C::CoordinateLength>, C::Scalar>: LineValid,
{
    r: Array<C::CoordinateLength>,
    s: C::Scalar,
    phantom_data: PhantomData<D>,
}

impl<C, D> LineValid for Schnorr<C, D>
where
    C: Curve,
    D: Default + Update + FixedOutput<OutputSize = <C::Scalar as LineValid>::Length>,
    Concat<Array<C::CoordinateLength>, C::Scalar>: LineValid,
{
    type Length = <Concat<Array<C::CoordinateLength>, C::Scalar> as LineValid>::Length;

    fn try_clone_array(a: &Array<Self::Length>) -> Result<Self, ()> {
        Concat::try_clone_array(a).map(|Concat(r, s)| Schnorr {
            r: r,
            s: s,
            phantom_data: PhantomData,
        })
    }

    fn clone_line(&self) -> Array<Self::Length> {
        use generic_array::typenum::Unsigned;

        let mut x = GenericArray::default();
        let m = <<C::Scalar as LineValid>::Length as Unsigned>::USIZE;
        x[..m].clone_from_slice(self.r.clone_line().as_ref());
        x[m..].clone_from_slice(self.s.clone_line().as_ref());
        x
    }
}

impl<C, D> Signature for Schnorr<C, D>
where
    C: Curve,
    D: Default + Update + FixedOutput<OutputSize = <C::Scalar as LineValid>::Length>,
    Concat<Array<C::CoordinateLength>, C::Scalar>: LineValid,
{
    type Scalar = C::Scalar;
    type Curve = C;

    fn sign<M>(secret_key: &Self::Scalar, message: &M, seed: &Self::Scalar) -> Result<Self, ()>
    where
        M: AsRef<[u8]>,
    {
        let d = secret_key;
        let k = seed;
        let q = C::base().exp_ec(k);
        let r = q.x_coordinate();
        let h = D::default()
            .chain(r.clone_line())
            .chain(message)
            .finalize_fixed();
        let h = LineValid::try_clone_array(&h)?;
        let s = k.sub_ff(&(d.mul_ff(&h)?))?;
        Ok(Schnorr {
            r: r,
            s: s,
            phantom_data: PhantomData,
        })
    }

    fn verify<M>(&self, public_key: &Self::Curve, message: &M) -> Result<(), ()>
    where
        M: AsRef<[u8]>,
    {
        let &Schnorr {
            r: ref r, s: ref s, ..
        } = self;
        let y = public_key;
        let h = D::default()
            .chain(r.clone_line())
            .chain(message)
            .finalize_fixed();
        let h = LineValid::try_clone_array(&h)?;
        let qk = y.exp_ec(&h).mul_ec(&C::base().exp_ec(&s));
        if qk.x_coordinate().eq(r) {
            Ok(())
        } else {
            Err(())
        }
    }
}

#[cfg(all(test, feature = "curve25519-dalek"))]
#[test]
fn signature() {
    use curve25519_dalek::{edwards::EdwardsPoint, scalar::Scalar};
    use generic_array::sequence::GenericSequence;

    let seed = Scalar::try_clone_array(&GenericArray::generate(|_| rand::random())).unwrap();
    let sk = Scalar::try_clone_array(&GenericArray::generate(|_| rand::random())).unwrap();
    let pk = EdwardsPoint::base().exp_ec(&sk);

    let message = [1, 2, 3, 4];
    let signature = Schnorr::<EdwardsPoint, sha3::Sha3_256>::sign(&sk, &message, &seed).unwrap();
    signature.verify(&pk, &message).unwrap();
}