/* aes_decrypt.c - TinyCrypt implementation of AES decryption procedure */

/*
    Copyright (C) 2017 by Intel Corporation, All Rights Reserved.

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions are met:

      - Redistributions of source code must retain the above copyright notice,
       this list of conditions and the following disclaimer.

      - Redistributions in binary form must reproduce the above copyright
      notice, this list of conditions and the following disclaimer in the
      documentation and/or other materials provided with the distribution.

      - Neither the name of Intel Corporation nor the names of its contributors
      may be used to endorse or promote products derived from this software
      without specific prior written permission.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
    AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
    IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
    ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
    LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
    CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
    SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
    INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
    CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
    ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
    POSSIBILITY OF SUCH DAMAGE.
*/

#include <tinycrypt/aes.h>
#include <tinycrypt/constants.h>
#include <tinycrypt/utils.h>

static const uint8_t inv_sbox[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
};

int tc_aes128_set_decrypt_key(TCAesKeySched_t s, const uint8_t* k)
{
    return tc_aes128_set_encrypt_key(s, k);
}

#define mult8(a)(_double_byte(_double_byte(_double_byte(a))))
#define mult9(a)(mult8(a)^(a))
#define multb(a)(mult8(a)^_double_byte(a)^(a))
#define multd(a)(mult8(a)^_double_byte(_double_byte(a))^(a))
#define multe(a)(mult8(a)^_double_byte(_double_byte(a))^_double_byte(a))

static inline void mult_row_column(uint8_t* out, const uint8_t* in)
{
    out[0] = multe(in[0]) ^ multb(in[1]) ^ multd(in[2]) ^ mult9(in[3]);
    out[1] = mult9(in[0]) ^ multe(in[1]) ^ multb(in[2]) ^ multd(in[3]);
    out[2] = multd(in[0]) ^ mult9(in[1]) ^ multe(in[2]) ^ multb(in[3]);
    out[3] = multb(in[0]) ^ multd(in[1]) ^ mult9(in[2]) ^ multe(in[3]);
}

static inline void inv_mix_columns(uint8_t* s)
{
    uint8_t t[Nb*Nk];
    mult_row_column(t, s);
    mult_row_column(&t[Nb], s+Nb);
    mult_row_column(&t[2*Nb], s+(2*Nb));
    mult_row_column(&t[3*Nb], s+(3*Nb));
    (void)_copy(s, sizeof(t), t, sizeof(t));
}

static inline void add_round_key(uint8_t* s, const unsigned int* k)
{
    s[0] ^= (uint8_t)(k[0] >> 24);
    s[1] ^= (uint8_t)(k[0] >> 16);
    s[2] ^= (uint8_t)(k[0] >> 8);
    s[3] ^= (uint8_t)(k[0]);
    s[4] ^= (uint8_t)(k[1] >> 24);
    s[5] ^= (uint8_t)(k[1] >> 16);
    s[6] ^= (uint8_t)(k[1] >> 8);
    s[7] ^= (uint8_t)(k[1]);
    s[8] ^= (uint8_t)(k[2] >> 24);
    s[9] ^= (uint8_t)(k[2] >> 16);
    s[10] ^= (uint8_t)(k[2] >> 8);
    s[11] ^= (uint8_t)(k[2]);
    s[12] ^= (uint8_t)(k[3] >> 24);
    s[13] ^= (uint8_t)(k[3] >> 16);
    s[14] ^= (uint8_t)(k[3] >> 8);
    s[15] ^= (uint8_t)(k[3]);
}

static inline void inv_sub_bytes(uint8_t* s)
{
    unsigned int i;

    for (i = 0; i < (Nb*Nk); ++i)
    {
        s[i] = inv_sbox[s[i]];
    }
}

/*
    This inv_shift_rows also implements the matrix flip required for
    inv_mix_columns, but performs it here to reduce the number of memory
    operations.
*/
static inline void inv_shift_rows(uint8_t* s)
{
    uint8_t t[Nb*Nk];
    t[0]  = s[0];
    t[1] = s[13];
    t[2] = s[10];
    t[3] = s[7];
    t[4]  = s[4];
    t[5] = s[1];
    t[6] = s[14];
    t[7] = s[11];
    t[8]  = s[8];
    t[9] = s[5];
    t[10] = s[2];
    t[11] = s[15];
    t[12] = s[12];
    t[13] = s[9];
    t[14] = s[6];
    t[15] = s[3];
    (void)_copy(s, sizeof(t), t, sizeof(t));
}

int tc_aes_decrypt(uint8_t* out, const uint8_t* in, const TCAesKeySched_t s)
{
    uint8_t state[Nk*Nb];
    unsigned int i;

    if (out == (uint8_t*) 0)
    {
        return TC_CRYPTO_FAIL;
    }
    else if (in == (const uint8_t*) 0)
    {
        return TC_CRYPTO_FAIL;
    }
    else if (s == (TCAesKeySched_t) 0)
    {
        return TC_CRYPTO_FAIL;
    }

    (void)_copy(state, sizeof(state), in, sizeof(state));
    add_round_key(state, s->words + Nb*Nr);

    for (i = Nr - 1; i > 0; --i)
    {
        inv_shift_rows(state);
        inv_sub_bytes(state);
        add_round_key(state, s->words + Nb*i);
        inv_mix_columns(state);
    }

    inv_shift_rows(state);
    inv_sub_bytes(state);
    add_round_key(state, s->words);
    (void)_copy(out, sizeof(state), state, sizeof(state));
    /*zeroing out the state buffer */
    _set(state, TC_ZERO_BYTE, sizeof(state));
    return TC_CRYPTO_SUCCESS;
}
