rustls/crypto/
tls12.rs

1use super::hmac;
2use super::ActiveKeyExchange;
3use crate::error::Error;
4
5use alloc::boxed::Box;
6
7/// Implements [`Prf`] using a [`hmac::Hmac`].
8pub struct PrfUsingHmac<'a>(pub &'a dyn hmac::Hmac);
9
10impl<'a> Prf for PrfUsingHmac<'a> {
11    fn for_key_exchange(
12        &self,
13        output: &mut [u8; 48],
14        kx: Box<dyn ActiveKeyExchange>,
15        peer_pub_key: &[u8],
16        label: &[u8],
17        seed: &[u8],
18    ) -> Result<(), Error> {
19        prf(
20            output,
21            self.0
22                .with_key(
23                    kx.complete(peer_pub_key)?
24                        .secret_bytes(),
25                )
26                .as_ref(),
27            label,
28            seed,
29        );
30        Ok(())
31    }
32
33    fn for_secret(&self, output: &mut [u8], secret: &[u8], label: &[u8], seed: &[u8]) {
34        prf(output, self.0.with_key(secret).as_ref(), label, seed);
35    }
36}
37
38/// An instantiation of the TLS1.2 PRF with a specific, implicit hash function.
39///
40/// See the definition in [RFC5246 section 5](https://www.rfc-editor.org/rfc/rfc5246#section-5).
41///
42/// See [`PrfUsingHmac`] as a route to implementing this trait with just
43/// an implementation of [`hmac::Hmac`].
44pub trait Prf: Send + Sync {
45    /// Computes `PRF(secret, label, seed)` using the secret from a completed key exchange.
46    ///
47    /// Completes the given key exchange, and then uses the resulting shared secret
48    /// to compute the PRF, writing the result into `output`.
49    ///
50    /// The caller guarantees that `label`, `seed` are non-empty. The caller makes no
51    /// guarantees about the contents of `peer_pub_key`. It must be validated by
52    /// [`ActiveKeyExchange::complete`].
53    fn for_key_exchange(
54        &self,
55        output: &mut [u8; 48],
56        kx: Box<dyn ActiveKeyExchange>,
57        peer_pub_key: &[u8],
58        label: &[u8],
59        seed: &[u8],
60    ) -> Result<(), Error>;
61
62    /// Computes `PRF(secret, label, seed)`, writing the result into `output`.
63    ///
64    /// The caller guarantees that `secret`, `label`, and `seed` are non-empty.
65    fn for_secret(&self, output: &mut [u8], secret: &[u8], label: &[u8], seed: &[u8]);
66}
67
68pub(crate) fn prf(out: &mut [u8], hmac_key: &dyn hmac::Key, label: &[u8], seed: &[u8]) {
69    // A(1)
70    let mut current_a = hmac_key.sign(&[label, seed]);
71
72    let chunk_size = hmac_key.tag_len();
73    for chunk in out.chunks_mut(chunk_size) {
74        // P_hash[i] = HMAC_hash(secret, A(i) + seed)
75        let p_term = hmac_key.sign(&[current_a.as_ref(), label, seed]);
76        chunk.copy_from_slice(&p_term.as_ref()[..chunk.len()]);
77
78        // A(i+1) = HMAC_hash(secret, A(i))
79        current_a = hmac_key.sign(&[current_a.as_ref()]);
80    }
81}
82
83#[cfg(all(test, feature = "ring"))]
84mod tests {
85    use crate::crypto::hmac::Hmac;
86    use crate::test_provider::hmac;
87
88    // Below known answer tests come from https://mailarchive.ietf.org/arch/msg/tls/fzVCzk-z3FShgGJ6DOXqM1ydxms/
89
90    #[test]
91    fn check_sha256() {
92        let secret = b"\x9b\xbe\x43\x6b\xa9\x40\xf0\x17\xb1\x76\x52\x84\x9a\x71\xdb\x35";
93        let seed = b"\xa0\xba\x9f\x93\x6c\xda\x31\x18\x27\xa6\xf7\x96\xff\xd5\x19\x8c";
94        let label = b"test label";
95        let expect = include_bytes!("../testdata/prf-result.1.bin");
96        let mut output = [0u8; 100];
97
98        super::prf(
99            &mut output,
100            &*hmac::HMAC_SHA256.with_key(secret),
101            label,
102            seed,
103        );
104        assert_eq!(expect.len(), output.len());
105        assert_eq!(expect.to_vec(), output.to_vec());
106    }
107
108    #[test]
109    fn check_sha512() {
110        let secret = b"\xb0\x32\x35\x23\xc1\x85\x35\x99\x58\x4d\x88\x56\x8b\xbb\x05\xeb";
111        let seed = b"\xd4\x64\x0e\x12\xe4\xbc\xdb\xfb\x43\x7f\x03\xe6\xae\x41\x8e\xe5";
112        let label = b"test label";
113        let expect = include_bytes!("../testdata/prf-result.2.bin");
114        let mut output = [0u8; 196];
115
116        super::prf(
117            &mut output,
118            &*hmac::HMAC_SHA512.with_key(secret),
119            label,
120            seed,
121        );
122        assert_eq!(expect.len(), output.len());
123        assert_eq!(expect.to_vec(), output.to_vec());
124    }
125
126    #[test]
127    fn check_sha384() {
128        let secret = b"\xb8\x0b\x73\x3d\x6c\xee\xfc\xdc\x71\x56\x6e\xa4\x8e\x55\x67\xdf";
129        let seed = b"\xcd\x66\x5c\xf6\xa8\x44\x7d\xd6\xff\x8b\x27\x55\x5e\xdb\x74\x65";
130        let label = b"test label";
131        let expect = include_bytes!("../testdata/prf-result.3.bin");
132        let mut output = [0u8; 148];
133
134        super::prf(
135            &mut output,
136            &*hmac::HMAC_SHA384.with_key(secret),
137            label,
138            seed,
139        );
140        assert_eq!(expect.len(), output.len());
141        assert_eq!(expect.to_vec(), output.to_vec());
142    }
143}
144
145#[cfg(all(bench, any(feature = "ring", feature = "aws_lc_rs")))]
146mod benchmarks {
147    #[bench]
148    fn bench_sha256(b: &mut test::Bencher) {
149        use crate::crypto::hmac::Hmac;
150        use crate::test_provider::hmac;
151
152        let label = &b"extended master secret"[..];
153        let seed = [0u8; 32];
154        let key = &b"secret"[..];
155
156        b.iter(|| {
157            let mut out = [0u8; 48];
158            super::prf(&mut out, &*hmac::HMAC_SHA256.with_key(key), &label, &seed);
159            test::black_box(out);
160        });
161    }
162}
rustls/crypto/tls12.rs

rustls/crypto/
tls12.rs
