const INITIAL_STATE: [u32; 8] = [
0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a, 0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19,
];
const ROUND_CONSTANTS: [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,
];
pub(super) struct Sha256 {
state: [u32; 8],
buffer: [u8; 64],
buffer_len: usize,
input_len: u64,
}
impl Sha256 {
pub(super) fn new() -> Self {
Self {
state: INITIAL_STATE,
buffer: [0; 64],
buffer_len: 0,
input_len: 0,
}
}
pub(super) fn update(&mut self, mut input: &[u8]) {
self.input_len = self
.input_len
.checked_add(u64::try_from(input.len()).expect("input length fits in u64"))
.expect("SHA-256 input is shorter than 2^64 bytes");
if self.buffer_len > 0 {
let copied = input.len().min(64 - self.buffer_len);
self.buffer[self.buffer_len..self.buffer_len + copied]
.copy_from_slice(&input[..copied]);
self.buffer_len += copied;
input = &input[copied..];
if self.buffer_len < 64 {
return;
}
compress(&mut self.state, &self.buffer);
self.buffer_len = 0;
}
let (blocks, remainder) = input.as_chunks::<64>();
for block in blocks {
compress(&mut self.state, block);
}
self.buffer[..remainder.len()].copy_from_slice(remainder);
self.buffer_len = remainder.len();
}
pub(super) fn finalize(mut self) -> [u8; 32] {
let bit_len = self.input_len.wrapping_mul(8);
self.buffer[self.buffer_len] = 0x80;
self.buffer_len += 1;
if self.buffer_len > 56 {
self.buffer[self.buffer_len..].fill(0);
compress(&mut self.state, &self.buffer);
self.buffer.fill(0);
} else {
self.buffer[self.buffer_len..56].fill(0);
}
self.buffer[56..].copy_from_slice(&bit_len.to_be_bytes());
compress(&mut self.state, &self.buffer);
let mut digest = [0; 32];
for (output, word) in digest.as_chunks_mut::<4>().0.iter_mut().zip(self.state) {
output.copy_from_slice(&word.to_be_bytes());
}
digest
}
}
fn compress(state: &mut [u32; 8], block: &[u8; 64]) {
let mut schedule = [0_u32; 64];
for (word, bytes) in schedule.iter_mut().zip(block.as_chunks::<4>().0) {
*word = u32::from_be_bytes(*bytes);
}
for index in 16..64 {
let s0 = schedule[index - 15].rotate_right(7)
^ schedule[index - 15].rotate_right(18)
^ (schedule[index - 15] >> 3);
let s1 = schedule[index - 2].rotate_right(17)
^ schedule[index - 2].rotate_right(19)
^ (schedule[index - 2] >> 10);
schedule[index] = schedule[index - 16]
.wrapping_add(s0)
.wrapping_add(schedule[index - 7])
.wrapping_add(s1);
}
let [mut a, mut b, mut c, mut d, mut e, mut f, mut g, mut h] = *state;
for (word, constant) in schedule.into_iter().zip(ROUND_CONSTANTS) {
let choice = (e & f) ^ (!e & g);
let majority = (a & b) ^ (a & c) ^ (b & c);
let sum0 = a.rotate_right(2) ^ a.rotate_right(13) ^ a.rotate_right(22);
let sum1 = e.rotate_right(6) ^ e.rotate_right(11) ^ e.rotate_right(25);
let temporary1 = h
.wrapping_add(sum1)
.wrapping_add(choice)
.wrapping_add(constant)
.wrapping_add(word);
let temporary2 = sum0.wrapping_add(majority);
h = g;
g = f;
f = e;
e = d.wrapping_add(temporary1);
d = c;
c = b;
b = a;
a = temporary1.wrapping_add(temporary2);
}
for (value, compressed) in state.iter_mut().zip([a, b, c, d, e, f, g, h]) {
*value = value.wrapping_add(compressed);
}
}
#[cfg(test)]
mod tests;