libsm 0.6.0

A Rust Library of China's Standards of Encryption Algorithms (SM2/3/4)
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

use num_bigint::BigUint;
use num_traits::One;

use super::ecc::{EccCtx, Point};
use crate::sm2::error::{Sm2Error, Sm2Result};
use crate::{sm2::util::kdf, sm3::hash::Sm3Hash};

pub struct EncryptCtx {
    klen: usize,
    curve: EccCtx,
    pk_b: Point,
}

pub struct DecryptCtx {
    klen: usize,
    curve: EccCtx,
    sk_b: BigUint,
}

impl EncryptCtx {
    pub fn new(klen: usize, pk_b: Point) -> EncryptCtx {
        EncryptCtx {
            klen,
            curve: EccCtx::new(),
            pk_b,
        }
    }

    // klen bytes, result: C1+C2+C3
    pub fn encrypt(&self, msg: &[u8]) -> Sm2Result<Vec<u8>> {
        loop {
            let k = self.curve.random_uint();
            let c_1_point = self.curve.g_mul(&k)?;
            let h = BigUint::one();
            let s_point = self.curve.mul(&h, &self.pk_b)?;
            if s_point.is_zero() {
                return Err(Sm2Error::ZeroPoint);
            }

            let c_2_point = self.curve.mul(&k, &self.pk_b)?;
            let (x_2, y_2) = self.curve.to_affine(&c_2_point)?;
            let x_2_bytes = x_2.to_bytes();
            let y_2_bytes = y_2.to_bytes();

            let mut prepend: Vec<u8> = vec![];
            prepend.extend_from_slice(&x_2_bytes);
            prepend.extend_from_slice(&y_2_bytes);
            let mut t = kdf(&prepend, self.klen);

            let mut flag = true;
            for elem in &t {
                if elem != &0 {
                    flag = false;
                    break;
                }
            }

            if !flag {
                for i in 0..t.len() {
                    t[i] ^= msg[i];
                }
                let mut prepend: Vec<u8> = vec![];
                prepend.extend_from_slice(&x_2_bytes);
                prepend.extend_from_slice(msg);
                prepend.extend_from_slice(&y_2_bytes);
                let c_3 = Sm3Hash::new(&prepend).get_hash();
                let c_1_bytes = self.curve.point_to_bytes(&c_1_point, false)?;

                let a = [c_1_bytes, t, c_3.to_vec()].concat();
                return Ok(a);
            }
        }
    }
}

impl DecryptCtx {
    pub fn new(klen: usize, sk_b: BigUint) -> DecryptCtx {
        DecryptCtx {
            klen,
            curve: EccCtx::new(),
            sk_b,
        }
    }

    pub fn decrypt(&self, cipher: &[u8]) -> Sm2Result<Vec<u8>> {
        let c_1_bytes = &cipher[0..65];
        let c_1_point = self.curve.bytes_to_point(c_1_bytes)?;
        // if c_1_point not in curve, return error, todo return error
        if !self.curve.check_point(&c_1_point)? {
            return Err(Sm2Error::CheckPointErr);
        }
        let h = BigUint::one();
        let s_point = self.curve.mul(&h, &c_1_point)?;
        // todo return error
        if s_point.is_zero() {
            return Err(Sm2Error::ZeroPoint);
        }

        let c_2_point = self.curve.mul(&self.sk_b, &c_1_point)?;
        let (x_2, y_2) = self.curve.to_affine(&c_2_point)?;
        let x_2_bytes = x_2.to_bytes();
        let y_2_bytes = y_2.to_bytes();

        let mut prepend: Vec<u8> = vec![];
        prepend.extend_from_slice(&x_2_bytes);
        prepend.extend_from_slice(&y_2_bytes);
        let t = kdf(&prepend, self.klen);
        let mut flag = true;
        for elem in &t {
            if elem != &0 {
                flag = false;
                break;
            }
        }
        if flag {
            return Err(Sm2Error::ZeroData);
        }
        let mut c_2 = cipher[65..(65 + self.klen)].to_vec();
        for i in 0..self.klen {
            c_2[i] ^= t[i];
        }
        let mut prepend: Vec<u8> = vec![];
        prepend.extend_from_slice(&x_2_bytes);
        prepend.extend_from_slice(&c_2);
        prepend.extend_from_slice(&y_2_bytes);
        let c_3 = &cipher[(65 + self.klen)..];
        let u = Sm3Hash::new(&prepend).get_hash();
        if c_3 != u {
            return Err(Sm2Error::HashNotEqual);
        }
        Ok(c_2)
    }
}

#[cfg(test)]
mod tests {
    use crate::sm2::signature::SigCtx;

    use super::*;

    #[test]
    fn sm2_encrypt_decrypt_test() {
        let msg = "hello world".as_bytes();
        let klen = msg.len();
        let ctx = SigCtx::new();
        let (pk_b, sk_b) = ctx.new_keypair().unwrap();

        let encrypt_ctx = EncryptCtx::new(klen, pk_b);
        let cipher = encrypt_ctx.encrypt(msg).unwrap();

        let decrypt_ctx = DecryptCtx::new(klen, sk_b);
        let plain = decrypt_ctx.decrypt(&cipher).unwrap();
        assert_eq!(msg, plain);
    }
}