fix: strengthen resource fingerprints

1 files changed, 192 insertions, 0 deletions

diff --git a/crates/fparkan-binary/src/lib.rs b/crates/fparkan-binary/src/lib.rs
index ef5a0e4..793719a 100644
--- a/crates/fparkan-binary/src/lib.rs
+++ b/crates/fparkan-binary/src/lib.rs
@@ -3,6 +3,9 @@
 
 use std::fmt;
 
+/// SHA-256 digest bytes.
+pub type Sha256Digest = [u8; 32];
+
 /// Parser limits shared by binary formats.
 #[derive(Clone, Copy, Debug)]
 pub struct Limits {
@@ -262,6 +265,183 @@ pub fn read_lp_bytes(cursor: &mut Cursor<'_>, max: u32) -> Result<Vec<u8>, Decod
     Ok(cursor.read_exact(len)?.to_vec())
 }
 
+/// Computes a SHA-256 content digest without external dependencies.
+#[must_use]
+pub fn sha256(bytes: &[u8]) -> Sha256Digest {
+    const K: [u32; 64] = [
+        0x428a_2f98,
+        0x7137_4491,
+        0xb5c0_fbcf,
+        0xe9b5_dba5,
+        0x3956_c25b,
+        0x59f1_11f1,
+        0x923f_82a4,
+        0xab1c_5ed5,
+        0xd807_aa98,
+        0x1283_5b01,
+        0x2431_85be,
+        0x550c_7dc3,
+        0x72be_5d74,
+        0x80de_b1fe,
+        0x9bdc_06a7,
+        0xc19b_f174,
+        0xe49b_69c1,
+        0xefbe_4786,
+        0x0fc1_9dc6,
+        0x240c_a1cc,
+        0x2de9_2c6f,
+        0x4a74_84aa,
+        0x5cb0_a9dc,
+        0x76f9_88da,
+        0x983e_5152,
+        0xa831_c66d,
+        0xb003_27c8,
+        0xbf59_7fc7,
+        0xc6e0_0bf3,
+        0xd5a7_9147,
+        0x06ca_6351,
+        0x1429_2967,
+        0x27b7_0a85,
+        0x2e1b_2138,
+        0x4d2c_6dfc,
+        0x5338_0d13,
+        0x650a_7354,
+        0x766a_0abb,
+        0x81c2_c92e,
+        0x9272_2c85,
+        0xa2bf_e8a1,
+        0xa81a_664b,
+        0xc24b_8b70,
+        0xc76c_51a3,
+        0xd192_e819,
+        0xd699_0624,
+        0xf40e_3585,
+        0x106a_a070,
+        0x19a4_c116,
+        0x1e37_6c08,
+        0x2748_774c,
+        0x34b0_bcb5,
+        0x391c_0cb3,
+        0x4ed8_aa4a,
+        0x5b9c_ca4f,
+        0x682e_6ff3,
+        0x748f_82ee,
+        0x78a5_636f,
+        0x84c8_7814,
+        0x8cc7_0208,
+        0x90be_fffa,
+        0xa450_6ceb,
+        0xbef9_a3f7,
+        0xc671_78f2,
+    ];
+    let mut h = [
+        0x6a09_e667,
+        0xbb67_ae85,
+        0x3c6e_f372,
+        0xa54f_f53a,
+        0x510e_527f,
+        0x9b05_688c,
+        0x1f83_d9ab,
+        0x5be0_cd19,
+    ];
+
+    let bit_len = (bytes.len() as u64).wrapping_mul(8);
+    let mut chunks = bytes.chunks_exact(64);
+    for chunk in &mut chunks {
+        compress_sha256_chunk(&mut h, chunk, &K);
+    }
+
+    let tail = chunks.remainder();
+    let mut block = [0u8; 128];
+    block[..tail.len()].copy_from_slice(tail);
+    block[tail.len()] = 0x80;
+    let padded_len = if tail.len() < 56 { 64 } else { 128 };
+    block[padded_len - 8..padded_len].copy_from_slice(&bit_len.to_be_bytes());
+    for chunk in block[..padded_len].chunks_exact(64) {
+        compress_sha256_chunk(&mut h, chunk, &K);
+    }
+
+    let mut out = [0u8; 32];
+    for (idx, word) in h.iter().enumerate() {
+        out[idx * 4..idx * 4 + 4].copy_from_slice(&word.to_be_bytes());
+    }
+    out
+}
+
+/// Renders a SHA-256 digest as lowercase hexadecimal.
+#[must_use]
+pub fn sha256_hex(digest: &Sha256Digest) -> String {
+    const HEX: &[u8; 16] = b"0123456789abcdef";
+    let mut out = String::with_capacity(64);
+    for byte in digest {
+        out.push(char::from(HEX[usize::from(byte >> 4)]));
+        out.push(char::from(HEX[usize::from(byte & 0x0f)]));
+    }
+    out
+}
+
+#[allow(clippy::many_single_char_names)]
+fn compress_sha256_chunk(h: &mut [u32; 8], chunk: &[u8], k: &[u32; 64]) {
+    let mut w = [0u32; 64];
+    for (idx, word) in w.iter_mut().take(16).enumerate() {
+        let base = idx * 4;
+        *word = u32::from_be_bytes([
+            chunk[base],
+            chunk[base + 1],
+            chunk[base + 2],
+            chunk[base + 3],
+        ]);
+    }
+    for idx in 16..64 {
+        let s0 = w[idx - 15].rotate_right(7) ^ w[idx - 15].rotate_right(18) ^ (w[idx - 15] >> 3);
+        let s1 = w[idx - 2].rotate_right(17) ^ w[idx - 2].rotate_right(19) ^ (w[idx - 2] >> 10);
+        w[idx] = w[idx - 16]
+            .wrapping_add(s0)
+            .wrapping_add(w[idx - 7])
+            .wrapping_add(s1);
+    }
+
+    let mut a = h[0];
+    let mut b = h[1];
+    let mut c = h[2];
+    let mut d = h[3];
+    let mut e = h[4];
+    let mut f = h[5];
+    let mut g = h[6];
+    let mut hh = h[7];
+
+    for idx in 0..64 {
+        let s1 = e.rotate_right(6) ^ e.rotate_right(11) ^ e.rotate_right(25);
+        let ch = (e & f) ^ ((!e) & g);
+        let temp1 = hh
+            .wrapping_add(s1)
+            .wrapping_add(ch)
+            .wrapping_add(k[idx])
+            .wrapping_add(w[idx]);
+        let s0 = a.rotate_right(2) ^ a.rotate_right(13) ^ a.rotate_right(22);
+        let maj = (a & b) ^ (a & c) ^ (b & c);
+        let temp2 = s0.wrapping_add(maj);
+
+        hh = g;
+        g = f;
+        f = e;
+        e = d.wrapping_add(temp1);
+        d = c;
+        c = b;
+        b = a;
+        a = temp1.wrapping_add(temp2);
+    }
+
+    h[0] = h[0].wrapping_add(a);
+    h[1] = h[1].wrapping_add(b);
+    h[2] = h[2].wrapping_add(c);
+    h[3] = h[3].wrapping_add(d);
+    h[4] = h[4].wrapping_add(e);
+    h[5] = h[5].wrapping_add(f);
+    h[6] = h[6].wrapping_add(g);
+    h[7] = h[7].wrapping_add(hh);
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -305,4 +485,16 @@ mod tests {
         );
         assert_eq!(cursor.offset(), 4);
     }
+
+    #[test]
+    fn sha256_matches_known_vectors() {
+        assert_eq!(
+            sha256_hex(&sha256(b"")),
+            "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"
+        );
+        assert_eq!(
+            sha256_hex(&sha256(b"abc")),
+            "ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad"
+        );
+    }
 }