rustls/tls12/
prf.rs

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1use ring::hmac;
2
3fn concat_sign(key: &hmac::Key, a: &[u8], b: &[u8]) -> hmac::Tag {
4    let mut ctx = hmac::Context::with_key(key);
5    ctx.update(a);
6    ctx.update(b);
7    ctx.sign()
8}
9
10fn p(out: &mut [u8], alg: hmac::Algorithm, secret: &[u8], seed: &[u8]) {
11    let hmac_key = hmac::Key::new(alg, secret);
12
13    // A(1)
14    let mut current_a = hmac::sign(&hmac_key, seed);
15    let chunk_size = alg.digest_algorithm().output_len();
16    for chunk in out.chunks_mut(chunk_size) {
17        // P_hash[i] = HMAC_hash(secret, A(i) + seed)
18        let p_term = concat_sign(&hmac_key, current_a.as_ref(), seed);
19        chunk.copy_from_slice(&p_term.as_ref()[..chunk.len()]);
20
21        // A(i+1) = HMAC_hash(secret, A(i))
22        current_a = hmac::sign(&hmac_key, current_a.as_ref());
23    }
24}
25
26fn concat(a: &[u8], b: &[u8]) -> Vec<u8> {
27    let mut ret = Vec::new();
28    ret.extend_from_slice(a);
29    ret.extend_from_slice(b);
30    ret
31}
32
33pub(crate) fn prf(out: &mut [u8], alg: hmac::Algorithm, secret: &[u8], label: &[u8], seed: &[u8]) {
34    let joined_seed = concat(label, seed);
35    p(out, alg, secret, &joined_seed);
36}
37
38#[cfg(test)]
39mod tests {
40    use ring::hmac::{HMAC_SHA256, HMAC_SHA512};
41
42    #[test]
43    fn check_sha256() {
44        let secret = b"\x9b\xbe\x43\x6b\xa9\x40\xf0\x17\xb1\x76\x52\x84\x9a\x71\xdb\x35";
45        let seed = b"\xa0\xba\x9f\x93\x6c\xda\x31\x18\x27\xa6\xf7\x96\xff\xd5\x19\x8c";
46        let label = b"test label";
47        let expect = include_bytes!("../testdata/prf-result.1.bin");
48        let mut output = [0u8; 100];
49
50        super::prf(&mut output, HMAC_SHA256, secret, label, seed);
51        assert_eq!(expect.len(), output.len());
52        assert_eq!(expect.to_vec(), output.to_vec());
53    }
54
55    #[test]
56    fn check_sha512() {
57        let secret = b"\xb0\x32\x35\x23\xc1\x85\x35\x99\x58\x4d\x88\x56\x8b\xbb\x05\xeb";
58        let seed = b"\xd4\x64\x0e\x12\xe4\xbc\xdb\xfb\x43\x7f\x03\xe6\xae\x41\x8e\xe5";
59        let label = b"test label";
60        let expect = include_bytes!("../testdata/prf-result.2.bin");
61        let mut output = [0u8; 196];
62
63        super::prf(&mut output, HMAC_SHA512, secret, label, seed);
64        assert_eq!(expect.len(), output.len());
65        assert_eq!(expect.to_vec(), output.to_vec());
66    }
67}
68
69#[cfg(bench)]
70mod benchmarks {
71    #[bench]
72    fn bench_sha256(b: &mut test::Bencher) {
73        let label = &b"extended master secret"[..];
74        let seed = [0u8; 32];
75        let key = &b"secret"[..];
76
77        b.iter(|| {
78            let mut out = [0u8; 48];
79            super::prf(&mut out, ring::hmac::HMAC_SHA256, key, &label, &seed);
80            test::black_box(out);
81        });
82    }
83}
rustls/tls12/prf.rs

rustls/tls12/
prf.rs
