1
use std::{
2
    ops::{Mul, Rem, Shr},
3
    sync::LazyLock,
4
};
5

            
6
use hkdf::Hkdf;
7
use num::{FromPrimitive, Integer, One, Zero};
8
use num_bigint_dig::BigUint;
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use sha2::Sha256;
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use zeroize::{Zeroize, Zeroizing};
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12
1
pub fn generate_public_key_for_secret_exchange(
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    private_key: impl AsRef<[u8]>,
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) -> Result<Vec<u8>, oo7::crypto::Error> {
15
2
    let private_key_uint = BigUint::from_bytes_be(private_key.as_ref());
16
2
    static DH_GENERATOR: LazyLock<BigUint> = LazyLock::new(|| BigUint::from_u64(0x2).unwrap());
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2
    let public_key_uint = powm_for_secret_exchange(&DH_GENERATOR, private_key_uint);
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19
2
    Ok(public_key_uint.to_bytes_be())
20
}
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22
1
pub fn generate_aes_key_for_secret_exchange(
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    private_key: impl AsRef<[u8]>,
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    server_public_key: impl AsRef<[u8]>,
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) -> Result<Zeroizing<Vec<u8>>, oo7::crypto::Error> {
26
2
    let server_public_key_uint = BigUint::from_bytes_be(server_public_key.as_ref());
27
2
    let private_key_uint = BigUint::from_bytes_be(private_key.as_ref());
28
1
    let common_secret = powm_for_secret_exchange(&server_public_key_uint, private_key_uint);
29

            
30
1
    let mut common_secret_bytes = common_secret.to_bytes_be();
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2
    let mut common_secret_padded = vec![0; 192 - common_secret_bytes.len()];
32
    // inefficient, but ok for now
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1
    common_secret_padded.append(&mut common_secret_bytes);
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35
    // hkdf
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    // input_keying_material
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1
    let ikm = common_secret_padded;
38
1
    let salt = None;
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    let info = [];
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41
    // output keying material
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2
    let mut okm = Zeroizing::new(vec![0; 16]);
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44
2
    let (_, hk) = Hkdf::<Sha256>::extract(salt, &ikm);
45
1
    hk.expand(&info, okm.as_mut())
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        .expect("hkdf expand should never fail");
47

            
48
1
    Ok(okm)
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}
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51
1
fn powm_for_secret_exchange(base: &BigUint, mut exp: BigUint) -> BigUint {
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    // for key exchange
53
1
    static DH_PRIME: LazyLock<BigUint> = LazyLock::new(|| {
54
1
        BigUint::from_bytes_be(&[
55
            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xC9, 0x0F, 0xDA, 0xA2, 0x21, 0x68,
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            0xC2, 0x34, 0xC4, 0xC6, 0x62, 0x8B, 0x80, 0xDC, 0x1C, 0xD1, 0x29, 0x02, 0x4E, 0x08,
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            0x8A, 0x67, 0xCC, 0x74, 0x02, 0x0B, 0xBE, 0xA6, 0x3B, 0x13, 0x9B, 0x22, 0x51, 0x4A,
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            0x08, 0x79, 0x8E, 0x34, 0x04, 0xDD, 0xEF, 0x95, 0x19, 0xB3, 0xCD, 0x3A, 0x43, 0x1B,
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            0x30, 0x2B, 0x0A, 0x6D, 0xF2, 0x5F, 0x14, 0x37, 0x4F, 0xE1, 0x35, 0x6D, 0x6D, 0x51,
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            0xC2, 0x45, 0xE4, 0x85, 0xB5, 0x76, 0x62, 0x5E, 0x7E, 0xC6, 0xF4, 0x4C, 0x42, 0xE9,
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            0xA6, 0x37, 0xED, 0x6B, 0x0B, 0xFF, 0x5C, 0xB6, 0xF4, 0x06, 0xB7, 0xED, 0xEE, 0x38,
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            0x6B, 0xFB, 0x5A, 0x89, 0x9F, 0xA5, 0xAE, 0x9F, 0x24, 0x11, 0x7C, 0x4B, 0x1F, 0xE6,
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            0x49, 0x28, 0x66, 0x51, 0xEC, 0xE4, 0x5B, 0x3D, 0xC2, 0x00, 0x7C, 0xB8, 0xA1, 0x63,
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            0xBF, 0x05, 0x98, 0xDA, 0x48, 0x36, 0x1C, 0x55, 0xD3, 0x9A, 0x69, 0x16, 0x3F, 0xA8,
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            0xFD, 0x24, 0xCF, 0x5F, 0x83, 0x65, 0x5D, 0x23, 0xDC, 0xA3, 0xAD, 0x96, 0x1C, 0x62,
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            0xF3, 0x56, 0x20, 0x85, 0x52, 0xBB, 0x9E, 0xD5, 0x29, 0x07, 0x70, 0x96, 0x96, 0x6D,
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            0x67, 0x0C, 0x35, 0x4E, 0x4A, 0xBC, 0x98, 0x04, 0xF1, 0x74, 0x6C, 0x08, 0xCA, 0x23,
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            0x73, 0x27, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
69
        ])
70
    });
71

            
72
1
    let mut base = base.clone();
73
1
    let mut result: BigUint = One::one();
74

            
75
3
    while !exp.is_zero() {
76
3
        if exp.is_odd() {
77
1
            result = result.mul(&base).rem(&*DH_PRIME);
78
        }
79
2
        exp = exp.shr(1);
80
1
        base = (&base).mul(&base).rem(&*DH_PRIME);
81
    }
82
1
    exp.zeroize();
83

            
84
1
    result
85
}