rns-crypto 0.1.9

use alloc::vec::Vec;

pub(crate) const S_BOX: [u8; 256] = [
    0x63, 0x7C, 0x77, 0x7B, 0xF2, 0x6B, 0x6F, 0xC5, 0x30, 0x01, 0x67, 0x2B, 0xFE, 0xD7, 0xAB, 0x76,
    0xCA, 0x82, 0xC9, 0x7D, 0xFA, 0x59, 0x47, 0xF0, 0xAD, 0xD4, 0xA2, 0xAF, 0x9C, 0xA4, 0x72, 0xC0,
    0xB7, 0xFD, 0x93, 0x26, 0x36, 0x3F, 0xF7, 0xCC, 0x34, 0xA5, 0xE5, 0xF1, 0x71, 0xD8, 0x31, 0x15,
    0x04, 0xC7, 0x23, 0xC3, 0x18, 0x96, 0x05, 0x9A, 0x07, 0x12, 0x80, 0xE2, 0xEB, 0x27, 0xB2, 0x75,
    0x09, 0x83, 0x2C, 0x1A, 0x1B, 0x6E, 0x5A, 0xA0, 0x52, 0x3B, 0xD6, 0xB3, 0x29, 0xE3, 0x2F, 0x84,
    0x53, 0xD1, 0x00, 0xED, 0x20, 0xFC, 0xB1, 0x5B, 0x6A, 0xCB, 0xBE, 0x39, 0x4A, 0x4C, 0x58, 0xCF,
    0xD0, 0xEF, 0xAA, 0xFB, 0x43, 0x4D, 0x33, 0x85, 0x45, 0xF9, 0x02, 0x7F, 0x50, 0x3C, 0x9F, 0xA8,
    0x51, 0xA3, 0x40, 0x8F, 0x92, 0x9D, 0x38, 0xF5, 0xBC, 0xB6, 0xDA, 0x21, 0x10, 0xFF, 0xF3, 0xD2,
    0xCD, 0x0C, 0x13, 0xEC, 0x5F, 0x97, 0x44, 0x17, 0xC4, 0xA7, 0x7E, 0x3D, 0x64, 0x5D, 0x19, 0x73,
    0x60, 0x81, 0x4F, 0xDC, 0x22, 0x2A, 0x90, 0x88, 0x46, 0xEE, 0xB8, 0x14, 0xDE, 0x5E, 0x0B, 0xDB,
    0xE0, 0x32, 0x3A, 0x0A, 0x49, 0x06, 0x24, 0x5C, 0xC2, 0xD3, 0xAC, 0x62, 0x91, 0x95, 0xE4, 0x79,
    0xE7, 0xC8, 0x37, 0x6D, 0x8D, 0xD5, 0x4E, 0xA9, 0x6C, 0x56, 0xF4, 0xEA, 0x65, 0x7A, 0xAE, 0x08,
    0xBA, 0x78, 0x25, 0x2E, 0x1C, 0xA6, 0xB4, 0xC6, 0xE8, 0xDD, 0x74, 0x1F, 0x4B, 0xBD, 0x8B, 0x8A,
    0x70, 0x3E, 0xB5, 0x66, 0x48, 0x03, 0xF6, 0x0E, 0x61, 0x35, 0x57, 0xB9, 0x86, 0xC1, 0x1D, 0x9E,
    0xE1, 0xF8, 0x98, 0x11, 0x69, 0xD9, 0x8E, 0x94, 0x9B, 0x1E, 0x87, 0xE9, 0xCE, 0x55, 0x28, 0xDF,
    0x8C, 0xA1, 0x89, 0x0D, 0xBF, 0xE6, 0x42, 0x68, 0x41, 0x99, 0x2D, 0x0F, 0xB0, 0x54, 0xBB, 0x16,
];

pub(crate) const INV_S_BOX: [u8; 256] = [
    0x52, 0x09, 0x6A, 0xD5, 0x30, 0x36, 0xA5, 0x38, 0xBF, 0x40, 0xA3, 0x9E, 0x81, 0xF3, 0xD7, 0xFB,
    0x7C, 0xE3, 0x39, 0x82, 0x9B, 0x2F, 0xFF, 0x87, 0x34, 0x8E, 0x43, 0x44, 0xC4, 0xDE, 0xE9, 0xCB,
    0x54, 0x7B, 0x94, 0x32, 0xA6, 0xC2, 0x23, 0x3D, 0xEE, 0x4C, 0x95, 0x0B, 0x42, 0xFA, 0xC3, 0x4E,
    0x08, 0x2E, 0xA1, 0x66, 0x28, 0xD9, 0x24, 0xB2, 0x76, 0x5B, 0xA2, 0x49, 0x6D, 0x8B, 0xD1, 0x25,
    0x72, 0xF8, 0xF6, 0x64, 0x86, 0x68, 0x98, 0x16, 0xD4, 0xA4, 0x5C, 0xCC, 0x5D, 0x65, 0xB6, 0x92,
    0x6C, 0x70, 0x48, 0x50, 0xFD, 0xED, 0xB9, 0xDA, 0x5E, 0x15, 0x46, 0x57, 0xA7, 0x8D, 0x9D, 0x84,
    0x90, 0xD8, 0xAB, 0x00, 0x8C, 0xBC, 0xD3, 0x0A, 0xF7, 0xE4, 0x58, 0x05, 0xB8, 0xB3, 0x45, 0x06,
    0xD0, 0x2C, 0x1E, 0x8F, 0xCA, 0x3F, 0x0F, 0x02, 0xC1, 0xAF, 0xBD, 0x03, 0x01, 0x13, 0x8A, 0x6B,
    0x3A, 0x91, 0x11, 0x41, 0x4F, 0x67, 0xDC, 0xEA, 0x97, 0xF2, 0xCF, 0xCE, 0xF0, 0xB4, 0xE6, 0x73,
    0x96, 0xAC, 0x74, 0x22, 0xE7, 0xAD, 0x35, 0x85, 0xE2, 0xF9, 0x37, 0xE8, 0x1C, 0x75, 0xDF, 0x6E,
    0x47, 0xF1, 0x1A, 0x71, 0x1D, 0x29, 0xC5, 0x89, 0x6F, 0xB7, 0x62, 0x0E, 0xAA, 0x18, 0xBE, 0x1B,
    0xFC, 0x56, 0x3E, 0x4B, 0xC6, 0xD2, 0x79, 0x20, 0x9A, 0xDB, 0xC0, 0xFE, 0x78, 0xCD, 0x5A, 0xF4,
    0x1F, 0xDD, 0xA8, 0x33, 0x88, 0x07, 0xC7, 0x31, 0xB1, 0x12, 0x10, 0x59, 0x27, 0x80, 0xEC, 0x5F,
    0x60, 0x51, 0x7F, 0xA9, 0x19, 0xB5, 0x4A, 0x0D, 0x2D, 0xE5, 0x7A, 0x9F, 0x93, 0xC9, 0x9C, 0xEF,
    0xA0, 0xE0, 0x3B, 0x4D, 0xAE, 0x2A, 0xF5, 0xB0, 0xC8, 0xEB, 0xBB, 0x3C, 0x83, 0x53, 0x99, 0x61,
    0x17, 0x2B, 0x04, 0x7E, 0xBA, 0x77, 0xD6, 0x26, 0xE1, 0x69, 0x14, 0x63, 0x55, 0x21, 0x0C, 0x7D,
];

pub(crate) const R_CON: [u8; 32] = [
    0x00, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40,
    0x80, 0x1B, 0x36, 0x6C, 0xD8, 0xAB, 0x4D, 0x9A,
    0x2F, 0x5E, 0xBC, 0x63, 0xC6, 0x97, 0x35, 0x6A,
    0xD4, 0xB3, 0x7D, 0xFA, 0xEF, 0xC5, 0x91, 0x39,
];

/// State as 4 columns of 4 bytes each (column-major, matching Python's list-of-lists).
/// s[i][j] means column i, row j.
pub(crate) type State = [[u8; 4]; 4];

pub(crate) fn bytes_to_matrix(text: &[u8]) -> State {
    let mut state = [[0u8; 4]; 4];
    for i in 0..4 {
        for j in 0..4 {
            state[i][j] = text[i * 4 + j];
        }
    }
    state
}

pub(crate) fn matrix_to_bytes(state: &State) -> [u8; 16] {
    let mut result = [0u8; 16];
    for i in 0..4 {
        for j in 0..4 {
            result[i * 4 + j] = state[i][j];
        }
    }
    result
}

pub(crate) fn xor_bytes(a: &[u8], b: &[u8]) -> Vec<u8> {
    a.iter().zip(b.iter()).map(|(x, y)| x ^ y).collect()
}

pub(crate) fn add_round_key(state: &mut State, key: &[Vec<u8>]) {
    for i in 0..4 {
        for j in 0..4 {
            state[i][j] ^= key[i][j];
        }
    }
}

pub(crate) fn sub_bytes(state: &mut State) {
    for i in 0..4 {
        for j in 0..4 {
            state[i][j] = S_BOX[state[i][j] as usize];
        }
    }
}

pub(crate) fn inv_sub_bytes(state: &mut State) {
    for i in 0..4 {
        for j in 0..4 {
            state[i][j] = INV_S_BOX[state[i][j] as usize];
        }
    }
}

pub(crate) fn shift_rows(state: &mut State) {
    // Row 1: shift left by 1
    let tmp = state[0][1];
    state[0][1] = state[1][1];
    state[1][1] = state[2][1];
    state[2][1] = state[3][1];
    state[3][1] = tmp;

    // Row 2: shift left by 2
    let tmp0 = state[0][2];
    let tmp1 = state[1][2];
    state[0][2] = state[2][2];
    state[1][2] = state[3][2];
    state[2][2] = tmp0;
    state[3][2] = tmp1;

    // Row 3: shift left by 3
    let tmp = state[3][3];
    state[3][3] = state[2][3];
    state[2][3] = state[1][3];
    state[1][3] = state[0][3];
    state[0][3] = tmp;
}

pub(crate) fn inv_shift_rows(state: &mut State) {
    // Row 1: shift right by 1
    let tmp = state[3][1];
    state[3][1] = state[2][1];
    state[2][1] = state[1][1];
    state[1][1] = state[0][1];
    state[0][1] = tmp;

    // Row 2: shift right by 2
    let tmp0 = state[0][2];
    let tmp1 = state[1][2];
    state[0][2] = state[2][2];
    state[1][2] = state[3][2];
    state[2][2] = tmp0;
    state[3][2] = tmp1;

    // Row 3: shift right by 3
    let tmp = state[0][3];
    state[0][3] = state[1][3];
    state[1][3] = state[2][3];
    state[2][3] = state[3][3];
    state[3][3] = tmp;
}

fn xtime(a: u8) -> u8 {
    if a & 0x80 != 0 {
        ((a << 1) ^ 0x1B) & 0xFF
    } else {
        a << 1
    }
}

fn mix_single_column(a: &mut [u8; 4]) {
    let t = a[0] ^ a[1] ^ a[2] ^ a[3];
    let u = a[0];
    a[0] ^= t ^ xtime(a[0] ^ a[1]);
    a[1] ^= t ^ xtime(a[1] ^ a[2]);
    a[2] ^= t ^ xtime(a[2] ^ a[3]);
    a[3] ^= t ^ xtime(a[3] ^ u);
}

pub(crate) fn mix_columns(state: &mut State) {
    for i in 0..4 {
        mix_single_column(&mut state[i]);
    }
}

pub(crate) fn inv_mix_columns(state: &mut State) {
    for i in 0..4 {
        let u = xtime(xtime(state[i][0] ^ state[i][2]));
        let v = xtime(xtime(state[i][1] ^ state[i][3]));
        state[i][0] ^= u;
        state[i][1] ^= v;
        state[i][2] ^= u;
        state[i][3] ^= v;
    }
    mix_columns(state);
}

/// Expand key into round key matrices. Used by both AES-128 and AES-256.
pub(crate) fn expand_key(master_key: &[u8], rounds: usize) -> Vec<Vec<Vec<u8>>> {
    let mut key_columns: Vec<Vec<u8>> = Vec::new();
    // Initialize with key material in 4-byte columns
    for i in (0..master_key.len()).step_by(4) {
        key_columns.push(master_key[i..i + 4].to_vec());
    }

    let iteration_size = master_key.len() / 4;
    let mut i = 1usize;

    while key_columns.len() < (rounds + 1) * 4 {
        let mut word = key_columns.last().unwrap().clone();

        if key_columns.len() % iteration_size == 0 {
            // Circular shift
            let first = word.remove(0);
            word.push(first);
            // S-box
            for b in word.iter_mut() {
                *b = S_BOX[*b as usize];
            }
            // XOR with R_CON
            word[0] ^= R_CON[i];
            i += 1;
        } else if master_key.len() == 32 && key_columns.len() % iteration_size == 4 {
            // Extra S-box for 256-bit keys
            for b in word.iter_mut() {
                *b = S_BOX[*b as usize];
            }
        }

        // XOR with equivalent word from previous iteration
        let prev = &key_columns[key_columns.len() - iteration_size];
        word = word.iter().zip(prev.iter()).map(|(a, b)| a ^ b).collect();
        key_columns.push(word);
    }

    // Group into 4x4 matrices
    key_columns
        .chunks(4)
        .map(|chunk| chunk.to_vec())
        .collect()
}

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

    #[test]
    fn test_bytes_to_matrix_roundtrip() {
        let data: [u8; 16] = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15];
        let matrix = bytes_to_matrix(&data);
        let result = matrix_to_bytes(&matrix);
        assert_eq!(data, result);
    }

    #[test]
    fn test_sub_bytes_inv_sub_bytes() {
        let original = bytes_to_matrix(&[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]);
        let mut state = original;
        sub_bytes(&mut state);
        assert_ne!(state, original);
        inv_sub_bytes(&mut state);
        assert_eq!(state, original);
    }

    #[test]
    fn test_shift_rows_inv_shift_rows() {
        let original = bytes_to_matrix(&[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]);
        let mut state = original;
        shift_rows(&mut state);
        assert_ne!(state, original);
        inv_shift_rows(&mut state);
        assert_eq!(state, original);
    }

    #[test]
    fn test_mix_columns_inv_mix_columns() {
        let original = bytes_to_matrix(&[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16]);
        let mut state = original;
        mix_columns(&mut state);
        assert_ne!(state, original);
        inv_mix_columns(&mut state);
        assert_eq!(state, original);
    }
}