gpt-forensic 0.2.1

Forensic GUID Partition Table (GPT) parser — structure, CRC integrity, primary/backup divergence, and anomaly detection
Documentation 
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//! SHA-256 (FIPS 180-4) — dependency-free, for evidence/chain-of-custody hashing.
//!
//! Forensic tools fingerprint structures so an analyst can prove they have not
//! changed between acquisitions. Implemented from scratch (like [`crate::crc32`])
//! to keep the crate dependency-light; validated against the NIST example
//! vectors.
//!
//! Reference: NIST FIPS 180-4, "Secure Hash Standard":
//! <https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.180-4.pdf>

// The round/init constants are reproduced verbatim from FIPS 180-4 (kept
// separator-free so they can be diffed against the standard), and the working
// variables a..h mirror the standard's notation.
#![allow(clippy::unreadable_literal, clippy::many_single_char_names)]

/// Round constants (first 32 bits of the fractional parts of the cube roots of
/// the first 64 primes). FIPS 180-4 §4.2.2.
const K: [u32; 64] = [
    0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
    0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3, 0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
    0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
    0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
    0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13, 0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
    0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
    0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
    0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208, 0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2,
];

/// Initial hash values (first 32 bits of the fractional parts of the square
/// roots of the first 8 primes). FIPS 180-4 §5.3.3.
const H0: [u32; 8] = [
    0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a, 0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19,
];

/// Compute the SHA-256 digest of `data`.
#[must_use]
pub fn digest(data: &[u8]) -> [u8; 32] {
    let mut h = H0;

    // Padding: append 0x80, then zeros, then the 64-bit big-endian bit length.
    let bit_len = (data.len() as u64).wrapping_mul(8);
    let mut msg = data.to_vec();
    msg.push(0x80);
    while msg.len() % 64 != 56 {
        msg.push(0);
    }
    msg.extend_from_slice(&bit_len.to_be_bytes());

    for block in msg.chunks_exact(64) {
        let mut w = [0u32; 64];
        for (i, word) in w.iter_mut().take(16).enumerate() {
            *word = u32::from_be_bytes([
                block[i * 4],
                block[i * 4 + 1],
                block[i * 4 + 2],
                block[i * 4 + 3],
            ]);
        }
        for i in 16..64 {
            let s0 = w[i - 15].rotate_right(7) ^ w[i - 15].rotate_right(18) ^ (w[i - 15] >> 3);
            let s1 = w[i - 2].rotate_right(17) ^ w[i - 2].rotate_right(19) ^ (w[i - 2] >> 10);
            w[i] = w[i - 16]
                .wrapping_add(s0)
                .wrapping_add(w[i - 7])
                .wrapping_add(s1);
        }

        let [mut a, mut b, mut c, mut d, mut e, mut f, mut g, mut hh] = h;
        for i in 0..64 {
            let s1 = e.rotate_right(6) ^ e.rotate_right(11) ^ e.rotate_right(25);
            let ch = (e & f) ^ ((!e) & g);
            let t1 = hh
                .wrapping_add(s1)
                .wrapping_add(ch)
                .wrapping_add(K[i])
                .wrapping_add(w[i]);
            let s0 = a.rotate_right(2) ^ a.rotate_right(13) ^ a.rotate_right(22);
            let maj = (a & b) ^ (a & c) ^ (b & c);
            let t2 = s0.wrapping_add(maj);
            hh = g;
            g = f;
            f = e;
            e = d.wrapping_add(t1);
            d = c;
            c = b;
            b = a;
            a = t1.wrapping_add(t2);
        }
        for (hv, v) in h.iter_mut().zip([a, b, c, d, e, f, g, hh]) {
            *hv = hv.wrapping_add(v);
        }
    }

    let mut out = [0u8; 32];
    for (i, word) in h.iter().enumerate() {
        out[i * 4..i * 4 + 4].copy_from_slice(&word.to_be_bytes());
    }
    out
}

/// Render a digest as a lowercase hex string.
#[must_use]
pub fn hex(digest: &[u8; 32]) -> String {
    let mut s = String::with_capacity(64);
    for b in digest {
        s.push(char::from_digit(u32::from(b >> 4), 16).unwrap());
        s.push(char::from_digit(u32::from(b & 0xf), 16).unwrap());
    }
    s
}