rust_web_server/core/sha256/
mod.rs

1//! SHA-256 (FIPS 180-4) and HMAC-SHA256 (RFC 2104), for code that must sign
2//! or verify without an optional crypto dependency — e.g. the MCP server's
3//! `requestState` (MCP 2026-07-28). Not constant-time beyond [`verify`]'s
4//! comparison; not for secrets that a timing side channel would expose.
5
6#[cfg(test)]
7mod tests;
8
9const K: [u32; 64] = [
10    0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
11    0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3, 0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
12    0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
13    0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
14    0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13, 0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
15    0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
16    0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
17    0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208, 0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2,
18];
19
20/// SHA-256 of `data`.
21pub fn sha256(data: &[u8]) -> [u8; 32] {
22    let mut h: [u32; 8] = [0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a, 0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19];
23    let mut message = data.to_vec();
24    message.push(0x80);
25    while message.len() % 64 != 56 {
26        message.push(0);
27    }
28    message.extend_from_slice(&((data.len() as u64).wrapping_mul(8)).to_be_bytes());
29    for block in message.chunks(64) {
30        let mut w = [0u32; 64];
31        for (i, word) in block.chunks(4).enumerate() {
32            w[i] = u32::from_be_bytes([word[0], word[1], word[2], word[3]]);
33        }
34        for i in 16..64 {
35            let s0 = w[i - 15].rotate_right(7) ^ w[i - 15].rotate_right(18) ^ (w[i - 15] >> 3);
36            let s1 = w[i - 2].rotate_right(17) ^ w[i - 2].rotate_right(19) ^ (w[i - 2] >> 10);
37            w[i] = w[i - 16].wrapping_add(s0).wrapping_add(w[i - 7]).wrapping_add(s1);
38        }
39        let [mut a, mut b, mut c, mut d, mut e, mut f, mut g, mut hh] = h;
40        for i in 0..64 {
41            let s1 = e.rotate_right(6) ^ e.rotate_right(11) ^ e.rotate_right(25);
42            let ch = (e & f) ^ (!e & g);
43            let t1 = hh.wrapping_add(s1).wrapping_add(ch).wrapping_add(K[i]).wrapping_add(w[i]);
44            let s0 = a.rotate_right(2) ^ a.rotate_right(13) ^ a.rotate_right(22);
45            let maj = (a & b) ^ (a & c) ^ (b & c);
46            let t2 = s0.wrapping_add(maj);
47            hh = g;
48            g = f;
49            f = e;
50            e = d.wrapping_add(t1);
51            d = c;
52            c = b;
53            b = a;
54            a = t1.wrapping_add(t2);
55        }
56        for (state, value) in h.iter_mut().zip([a, b, c, d, e, f, g, hh]) {
57            *state = state.wrapping_add(value);
58        }
59    }
60    let mut out = [0u8; 32];
61    for (i, word) in h.iter().enumerate() {
62        out[i * 4..i * 4 + 4].copy_from_slice(&word.to_be_bytes());
63    }
64    out
65}
66
67/// HMAC-SHA256 of `message` under `key`.
68pub fn hmac_sha256(key: &[u8], message: &[u8]) -> [u8; 32] {
69    let mut block = [0u8; 64];
70    if key.len() > 64 {
71        block[..32].copy_from_slice(&sha256(key));
72    } else {
73        block[..key.len()].copy_from_slice(key);
74    }
75    let mut inner: Vec<u8> = block.iter().map(|b| b ^ 0x36).collect();
76    inner.extend_from_slice(message);
77    let mut outer: Vec<u8> = block.iter().map(|b| b ^ 0x5c).collect();
78    outer.extend_from_slice(&sha256(&inner));
79    sha256(&outer)
80}
81
82/// Whether `mac` is the HMAC-SHA256 of `message` under `key`, compared in
83/// constant time.
84pub fn verify(key: &[u8], message: &[u8], mac: &[u8]) -> bool {
85    let expected = hmac_sha256(key, message);
86    mac.len() == expected.len() && mac.iter().zip(expected).fold(0u8, |diff, (a, b)| diff | (a ^ b)) == 0
87}
rust_web_server/core/sha256/mod.rs

rust_web_server/core/sha256/
mod.rs
