noxtls_crypto/hash/mdigest/

sha256.rs

// Copyright (c) 2019-2026, Argenox Technologies LLC
// All rights reserved.
//
// SPDX-License-Identifier: GPL-2.0-only OR LicenseRef-Argenox-Commercial-License
//
// This file is part of the NoxTLS Library.
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by the
// Free Software Foundation; version 2 of the License.
//
// Alternatively, this file may be used under the terms of a commercial
// license from Argenox Technologies LLC.
//
// See `noxtls/LICENSE` and `noxtls/LICENSE.md` in this repository for full details.
// CONTACT: info@argenox.com

use super::Digest;
use crate::internal_alloc::Vec;

/// Implements SHA-256 compression and streaming digest state.
#[derive(Debug, Clone)]
pub struct Sha256 {
    state: [u32; 8],
    buffer: [u8; 64],
    buffer_len: usize,
    bit_len: u64,
}

impl Default for Sha256 {
    /// Builds a SHA-256 hasher with standard IV constants and an empty buffer.
    ///
    /// # Returns
    ///
    /// Fresh [`Sha256`] in the initial state.
    ///
    /// # Panics
    ///
    /// This function does not panic.
    fn default() -> Self {
        Self {
            state: [
                0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a, 0x510e527f, 0x9b05688c, 0x1f83d9ab,
                0x5be0cd19,
            ],
            buffer: [0; 64],
            buffer_len: 0,
            bit_len: 0,
        }
    }
}

impl Sha256 {
    /// Creates a new SHA-256 hasher initialized with standard IV constants.
    ///
    /// # Returns
    /// A fresh `Sha256` instance with empty input state.
    ///
    /// # Panics
    ///
    /// This function does not panic.
    pub fn new() -> Self {
        Self::default()
    }

    /// Compresses one 512-bit SHA-256 message block into the eight working words.
    ///
    /// # Arguments
    ///
    /// * `self` — Running hasher whose `state` is updated.
    /// * `block` — One fully prepared 64-byte big-endian message block.
    ///
    /// # Returns
    ///
    /// `()`; folds the round function output into `self.state`.
    ///
    /// # Panics
    ///
    /// This function does not panic.
    fn compress(&mut self, block: &[u8; 64]) {
        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,
        ];
        let mut w = [0_u32; 64];
        for (i, chunk) in block.chunks_exact(4).enumerate().take(16) {
            w[i] = u32::from_be_bytes([chunk[0], chunk[1], chunk[2], chunk[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 = self.state[0];
        let mut b = self.state[1];
        let mut c = self.state[2];
        let mut d = self.state[3];
        let mut e = self.state[4];
        let mut f = self.state[5];
        let mut g = self.state[6];
        let mut h = self.state[7];

        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 temp1 = h
                .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 temp2 = s0.wrapping_add(maj);

            h = g;
            g = f;
            f = e;
            e = d.wrapping_add(temp1);
            d = c;
            c = b;
            b = a;
            a = temp1.wrapping_add(temp2);
        }

        self.state[0] = self.state[0].wrapping_add(a);
        self.state[1] = self.state[1].wrapping_add(b);
        self.state[2] = self.state[2].wrapping_add(c);
        self.state[3] = self.state[3].wrapping_add(d);
        self.state[4] = self.state[4].wrapping_add(e);
        self.state[5] = self.state[5].wrapping_add(f);
        self.state[6] = self.state[6].wrapping_add(g);
        self.state[7] = self.state[7].wrapping_add(h);
    }
}

impl Digest for Sha256 {
    /// Absorbs `data` into the running digest, compressing whenever 64 bytes accumulate.
    ///
    /// # Arguments
    ///
    /// * `self` — Running SHA-256 hasher.
    /// * `data` — Next message bytes to append.
    ///
    /// # Returns
    ///
    /// `()`.
    ///
    /// # Panics
    ///
    /// This function does not panic.
    fn update(&mut self, mut data: &[u8]) {
        self.bit_len = self.bit_len.wrapping_add((data.len() as u64) * 8);
        while !data.is_empty() {
            let to_copy = (64 - self.buffer_len).min(data.len());
            self.buffer[self.buffer_len..self.buffer_len + to_copy]
                .copy_from_slice(&data[..to_copy]);
            self.buffer_len += to_copy;
            data = &data[to_copy..];
            if self.buffer_len == 64 {
                let block = self.buffer;
                self.compress(&block);
                self.buffer_len = 0;
            }
        }
    }

    /// Finalizes SHA-256 padding and returns the 32-byte digest in a newly allocated vector.
    ///
    /// # Arguments
    ///
    /// * `self` — Consumed hasher holding buffered tail bytes and the bit length.
    ///
    /// # Returns
    ///
    /// [`Vec`] containing exactly 32 digest bytes (big-endian words from internal state).
    ///
    /// # Panics
    ///
    /// This function does not panic.
    fn finalize(mut self) -> Vec<u8> {
        self.buffer[self.buffer_len] = 0x80;
        self.buffer_len += 1;

        if self.buffer_len > 56 {
            self.buffer[self.buffer_len..].fill(0);
            let block = self.buffer;
            self.compress(&block);
            self.buffer_len = 0;
        }

        self.buffer[self.buffer_len..56].fill(0);
        self.buffer[56..64].copy_from_slice(&self.bit_len.to_be_bytes());
        let block = self.buffer;
        self.compress(&block);

        let mut out = Vec::with_capacity(32);
        for word in self.state {
            out.extend_from_slice(&word.to_be_bytes());
        }
        out
    }
}

/// Computes SHA-256 of `data` and returns the 32-byte digest.
///
/// # Arguments
/// * `data`: Input bytes to hash.
///
/// # Returns
/// A 32-byte SHA-256 digest.
///
/// # Panics
///
/// This function does not panic.
#[must_use]
pub fn sha256(data: &[u8]) -> [u8; 32] {
    let mut hasher = Sha256::new();
    hasher.update(data);
    let digest = hasher.finalize();
    let mut out = [0_u8; 32];
    out.copy_from_slice(&digest);
    out
}