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//! An implementation of the [SM4][1] block cipher.
//!
//! [1]: https://en.wikipedia.org/wiki/SM4_(cipher)

#![no_std]
#![doc(html_logo_url = "https://raw.githubusercontent.com/RustCrypto/meta/master/logo_small.png")]
#![forbid(unsafe_code)]
#![warn(rust_2018_idioms)]
#![allow(clippy::unreadable_literal)]

pub use block_cipher;

use block_cipher::consts::{U1, U16};
use block_cipher::generic_array::GenericArray;
use block_cipher::{BlockCipher, NewBlockCipher};
use byteorder::{ByteOrder, BE};

pub const SBOX: [u8; 256] = [
    0xd6, 0x90, 0xe9, 0xfe, 0xcc, 0xe1, 0x3d, 0xb7, 0x16, 0xb6, 0x14, 0xc2, 0x28, 0xfb, 0x2c, 0x05,
    0x2b, 0x67, 0x9a, 0x76, 0x2a, 0xbe, 0x04, 0xc3, 0xaa, 0x44, 0x13, 0x26, 0x49, 0x86, 0x06, 0x99,
    0x9c, 0x42, 0x50, 0xf4, 0x91, 0xef, 0x98, 0x7a, 0x33, 0x54, 0x0b, 0x43, 0xed, 0xcf, 0xac, 0x62,
    0xe4, 0xb3, 0x1c, 0xa9, 0xc9, 0x08, 0xe8, 0x95, 0x80, 0xdf, 0x94, 0xfa, 0x75, 0x8f, 0x3f, 0xa6,
    0x47, 0x07, 0xa7, 0xfc, 0xf3, 0x73, 0x17, 0xba, 0x83, 0x59, 0x3c, 0x19, 0xe6, 0x85, 0x4f, 0xa8,
    0x68, 0x6b, 0x81, 0xb2, 0x71, 0x64, 0xda, 0x8b, 0xf8, 0xeb, 0x0f, 0x4b, 0x70, 0x56, 0x9d, 0x35,
    0x1e, 0x24, 0x0e, 0x5e, 0x63, 0x58, 0xd1, 0xa2, 0x25, 0x22, 0x7c, 0x3b, 0x01, 0x21, 0x78, 0x87,
    0xd4, 0x00, 0x46, 0x57, 0x9f, 0xd3, 0x27, 0x52, 0x4c, 0x36, 0x02, 0xe7, 0xa0, 0xc4, 0xc8, 0x9e,
    0xea, 0xbf, 0x8a, 0xd2, 0x40, 0xc7, 0x38, 0xb5, 0xa3, 0xf7, 0xf2, 0xce, 0xf9, 0x61, 0x15, 0xa1,
    0xe0, 0xae, 0x5d, 0xa4, 0x9b, 0x34, 0x1a, 0x55, 0xad, 0x93, 0x32, 0x30, 0xf5, 0x8c, 0xb1, 0xe3,
    0x1d, 0xf6, 0xe2, 0x2e, 0x82, 0x66, 0xca, 0x60, 0xc0, 0x29, 0x23, 0xab, 0x0d, 0x53, 0x4e, 0x6f,
    0xd5, 0xdb, 0x37, 0x45, 0xde, 0xfd, 0x8e, 0x2f, 0x03, 0xff, 0x6a, 0x72, 0x6d, 0x6c, 0x5b, 0x51,
    0x8d, 0x1b, 0xaf, 0x92, 0xbb, 0xdd, 0xbc, 0x7f, 0x11, 0xd9, 0x5c, 0x41, 0x1f, 0x10, 0x5a, 0xd8,
    0x0a, 0xc1, 0x31, 0x88, 0xa5, 0xcd, 0x7b, 0xbd, 0x2d, 0x74, 0xd0, 0x12, 0xb8, 0xe5, 0xb4, 0xb0,
    0x89, 0x69, 0x97, 0x4a, 0x0c, 0x96, 0x77, 0x7e, 0x65, 0xb9, 0xf1, 0x09, 0xc5, 0x6e, 0xc6, 0x84,
    0x18, 0xf0, 0x7d, 0xec, 0x3a, 0xdc, 0x4d, 0x20, 0x79, 0xee, 0x5f, 0x3e, 0xd7, 0xcb, 0x39, 0x48,
];

pub const FK: [u32; 4] = [0xa3b1bac6, 0x56aa3350, 0x677d9197, 0xb27022dc];

pub const CK: [u32; 32] = [
    0x00070e15, 0x1c232a31, 0x383f464d, 0x545b6269, 0x70777e85, 0x8c939aa1, 0xa8afb6bd, 0xc4cbd2d9,
    0xe0e7eef5, 0xfc030a11, 0x181f262d, 0x343b4249, 0x50575e65, 0x6c737a81, 0x888f969d, 0xa4abb2b9,
    0xc0c7ced5, 0xdce3eaf1, 0xf8ff060d, 0x141b2229, 0x30373e45, 0x4c535a61, 0x686f767d, 0x848b9299,
    0xa0a7aeb5, 0xbcc3cad1, 0xd8dfe6ed, 0xf4fb0209, 0x10171e25, 0x2c333a41, 0x484f565d, 0x646b7279,
];

#[inline]
fn tau(a: u32) -> u32 {
    let mut buf = [0u8; 4];
    BE::write_u32(&mut buf, a);
    buf[0] = SBOX[buf[0] as usize];
    buf[1] = SBOX[buf[1] as usize];
    buf[2] = SBOX[buf[2] as usize];
    buf[3] = SBOX[buf[3] as usize];
    BE::read_u32(&buf)
}

/// L: linear transformation
#[inline]
fn el(b: u32) -> u32 {
    b ^ b.rotate_left(2) ^ b.rotate_left(10) ^ b.rotate_left(18) ^ b.rotate_left(24)
}

#[inline]
fn el_prime(b: u32) -> u32 {
    b ^ b.rotate_left(13) ^ b.rotate_left(23)
}

#[inline]
fn t(val: u32) -> u32 {
    el(tau(val))
}

#[inline]
fn t_prime(val: u32) -> u32 {
    el_prime(tau(val))
}

/// SM4 cipher
#[derive(Copy, Clone)]
pub struct Sm4 {
    rk: [u32; 32],
}

impl NewBlockCipher for Sm4 {
    type KeySize = U16;

    fn new(key: &GenericArray<u8, U16>) -> Self {
        let mut mk = [0u32; 4];
        let mut rk = [0u32; 32];
        BE::read_u32_into(key, &mut mk);
        let mut k = [mk[0] ^ FK[0], mk[1] ^ FK[1], mk[2] ^ FK[2], mk[3] ^ FK[3]];

        for i in 0..8 {
            k[0] ^= t_prime(k[1] ^ k[2] ^ k[3] ^ CK[i * 4]);
            k[1] ^= t_prime(k[2] ^ k[3] ^ k[0] ^ CK[i * 4 + 1]);
            k[2] ^= t_prime(k[3] ^ k[0] ^ k[1] ^ CK[i * 4 + 2]);
            k[3] ^= t_prime(k[0] ^ k[1] ^ k[2] ^ CK[i * 4 + 3]);

            rk[i * 4] = k[0];
            rk[i * 4 + 1] = k[1];
            rk[i * 4 + 2] = k[2];
            rk[i * 4 + 3] = k[3];
        }

        Sm4 { rk }
    }
}

impl BlockCipher for Sm4 {
    type BlockSize = U16;
    type ParBlocks = U1;

    fn encrypt_block(&self, block: &mut GenericArray<u8, U16>) {
        let mut x = [0u32; 4];
        BE::read_u32_into(block, &mut x);
        let rk = &self.rk;
        for i in 0..8 {
            x[0] ^= t(x[1] ^ x[2] ^ x[3] ^ rk[i * 4]);
            x[1] ^= t(x[2] ^ x[3] ^ x[0] ^ rk[i * 4 + 1]);
            x[2] ^= t(x[3] ^ x[0] ^ x[1] ^ rk[i * 4 + 2]);
            x[3] ^= t(x[0] ^ x[1] ^ x[2] ^ rk[i * 4 + 3]);
        }
        x = [x[3], x[2], x[1], x[0]];
        BE::write_u32_into(&x, block);
    }

    fn decrypt_block(&self, block: &mut GenericArray<u8, U16>) {
        let mut x = [0u32; 4];
        BE::read_u32_into(block, &mut x);
        let rk = &self.rk;
        for i in 0..8 {
            x[0] ^= t(x[1] ^ x[2] ^ x[3] ^ rk[31 - i * 4]);
            x[1] ^= t(x[2] ^ x[3] ^ x[0] ^ rk[31 - (i * 4 + 1)]);
            x[2] ^= t(x[3] ^ x[0] ^ x[1] ^ rk[31 - (i * 4 + 2)]);
            x[3] ^= t(x[0] ^ x[1] ^ x[2] ^ rk[31 - (i * 4 + 3)]);
        }
        x = [x[3], x[2], x[1], x[0]];
        BE::write_u32_into(&x, block);
    }
}