SOLIDWORKS Bridge

//! SHA-256, in plain Rust — for recording WHICH bytes a migration copied.
//!
//! `migrate_legacy` records every file it copies by (path, size, mtime, sha256 of
//! the copy), so a later start can tell "the same file" from "a file that has
//! changed since it was copied". The size and mtime are what it compares; the
//! digest is what lets a person — or the next adversary — prove afterwards which
//! bytes the copy held. No crate for it: the dependency list is two crates on
//! purpose, and FIPS 180-4 is short. Checked against the standard vectors below.

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,
];

/// A streaming SHA-256.
pub struct Sha256 {
    h: [u32; 8],
    buf: [u8; 64],
    buf_len: usize,
    total: u64,
}

impl Default for Sha256 {
    fn default() -> Self {
        Self::new()
    }
}

impl Sha256 {
    pub fn new() -> Sha256 {
        Sha256 {
            h: [
                0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a, 0x510e527f, 0x9b05688c, 0x1f83d9ab,
                0x5be0cd19,
            ],
            buf: [0; 64],
            buf_len: 0,
            total: 0,
        }
    }

    fn block(&mut self, block: &[u8]) {
        let mut w = [0u32; 64];
        for (i, word) in w.iter_mut().take(16).enumerate() {
            *word = u32::from_be_bytes([block[4 * i], block[4 * i + 1], block[4 * i + 2], block[4 * i + 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 h] = self.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 = 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 t2 = s0.wrapping_add(maj);
            h = g;
            g = f;
            f = e;
            e = d.wrapping_add(t1);
            d = c;
            c = b;
            b = a;
            a = t1.wrapping_add(t2);
        }
        for (x, y) in self.h.iter_mut().zip([a, b, c, d, e, f, g, h]) {
            *x = x.wrapping_add(y);
        }
    }

    pub fn update(&mut self, mut data: &[u8]) {
        self.total = self.total.wrapping_add(data.len() as u64);
        if self.buf_len > 0 {
            let take = (64 - self.buf_len).min(data.len());
            self.buf[self.buf_len..self.buf_len + take].copy_from_slice(&data[..take]);
            self.buf_len += take;
            data = &data[take..];
            if self.buf_len == 64 {
                let block = self.buf;
                self.block(&block);
                self.buf_len = 0;
            }
        }
        while data.len() >= 64 {
            self.block(&data[..64]);
            data = &data[64..];
        }
        if !data.is_empty() {
            self.buf[..data.len()].copy_from_slice(data);
            self.buf_len = data.len();
        }
    }

    pub fn hex(mut self) -> String {
        let bits = self.total.wrapping_mul(8);
        let mut pad = vec![0x80u8];
        let rem = (self.total as usize + 1) % 64;
        let zeros = if rem <= 56 { 56 - rem } else { 120 - rem };
        pad.extend(std::iter::repeat(0u8).take(zeros));
        pad.extend_from_slice(&bits.to_be_bytes());
        // `update` would count the padding into the length; feed it raw.
        let total = self.total;
        self.update(&pad);
        self.total = total;
        self.h.iter().map(|x| format!("{x:08x}")).collect()
    }
}

/// The digest of a byte slice.
pub fn hex_of(data: &[u8]) -> String {
    let mut s = Sha256::new();
    s.update(data);
    s.hex()
}

/// The digest of a file, streamed; `None` when it cannot be read.
pub fn hex_of_file(path: &std::path::Path) -> Option<String> {
    use std::io::Read;
    let mut f = std::fs::File::open(path).ok()?;
    let mut s = Sha256::new();
    let mut buf = vec![0u8; 1 << 20];
    loop {
        let n = f.read(&mut buf).ok()?;
        if n == 0 {
            return Some(s.hex());
        }
        s.update(&buf[..n]);
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn the_standard_vectors() {
        assert_eq!(hex_of(b""), "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855");
        assert_eq!(hex_of(b"abc"), "ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad");
        assert_eq!(
            hex_of(b"abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq"),
            "248d6a61d20638b8e5c026930c3e6039a33ce45964ff2167f6ecedd419db06c1"
        );
        let million = vec![b'a'; 1_000_000];
        assert_eq!(hex_of(&million), "cdc76e5c9914fb9281a1c7e284d73e67f1809a48a497200e046d39ccc7112cd0");
    }

    #[test]
    fn streaming_in_odd_pieces_gives_the_same_digest() {
        let data: Vec<u8> = (0..10_000u32).map(|i| (i * 7 % 256) as u8).collect();
        let mut s = Sha256::new();
        for chunk in data.chunks(37) {
            s.update(chunk);
        }
        assert_eq!(s.hex(), hex_of(&data));
    }
}