/* ccm_mode.c - TinyCrypt implementation of CCM mode */

/*
    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/ccm_mode.h>
#include <tinycrypt/constants.h>
#include <tinycrypt/utils.h>

#include <stdio.h>

int tc_ccm_config(TCCcmMode_t c, TCAesKeySched_t sched, uint8_t* nonce,
                  unsigned int nlen, unsigned int mlen)
{
    /* input sanity check: */
    if (c == (TCCcmMode_t) 0 ||
            sched == (TCAesKeySched_t) 0 ||
            nonce == (uint8_t*) 0)
    {
        return TC_CRYPTO_FAIL;
    }
    else if (nlen != 13)
    {
        return TC_CRYPTO_FAIL; /* The allowed nonce size is: 13. See documentation.*/
    }
    else if ((mlen < 4) || (mlen > 16) || (mlen & 1))
    {
        return TC_CRYPTO_FAIL; /* The allowed mac sizes are: 4, 6, 8, 10, 12, 14, 16.*/
    }

    c->mlen = mlen;
    c->sched = sched;
    c->nonce = nonce;
    return TC_CRYPTO_SUCCESS;
}

/**
    Variation of CBC-MAC mode used in CCM.
*/
static void ccm_cbc_mac(uint8_t* T, const uint8_t* data, unsigned int dlen,
                        unsigned int flag, TCAesKeySched_t sched)
{
    unsigned int i;

    if (flag > 0)
    {
        T[0] ^= (uint8_t)(dlen >> 8);
        T[1] ^= (uint8_t)(dlen);
        dlen += 2;
        i = 2;
    }
    else
    {
        i = 0;
    }

    while (i < dlen)
    {
        T[i++ % (Nb * Nk)] ^= *data++;

        if (((i % (Nb * Nk)) == 0) || dlen == i)
        {
            (void) tc_aes_encrypt(T, T, sched);
        }
    }
}

/**
    Variation of CTR mode used in CCM.
    The CTR mode used by CCM is slightly different than the conventional CTR
    mode (the counter is increased before encryption, instead of after
    encryption). Besides, it is assumed that the counter is stored in the last
    2 bytes of the nonce.
*/
static int ccm_ctr_mode(uint8_t* out, unsigned int outlen, const uint8_t* in,
                        unsigned int inlen, uint8_t* ctr, const TCAesKeySched_t sched)
{
    uint8_t buffer[TC_AES_BLOCK_SIZE];
    uint8_t nonce[TC_AES_BLOCK_SIZE];
    uint16_t block_num;
    unsigned int i;

    /* input sanity check: */
    if (out == (uint8_t*) 0 ||
            in == (uint8_t*) 0 ||
            ctr == (uint8_t*) 0 ||
            sched == (TCAesKeySched_t) 0 ||
            inlen == 0 ||
            outlen == 0 ||
            outlen != inlen)
    {
        return TC_CRYPTO_FAIL;
    }

    /* copy the counter to the nonce */
    (void) _copy(nonce, sizeof(nonce), ctr, sizeof(nonce));
    /* select the last 2 bytes of the nonce to be incremented */
    block_num = (uint16_t) ((nonce[14] << 8)|(nonce[15]));

    for (i = 0; i < inlen; ++i)
    {
        if ((i % (TC_AES_BLOCK_SIZE)) == 0)
        {
            block_num++;
            nonce[14] = (uint8_t)(block_num >> 8);
            nonce[15] = (uint8_t)(block_num);

            if (!tc_aes_encrypt(buffer, nonce, sched))
            {
                return TC_CRYPTO_FAIL;
            }
        }

        /* update the output */
        *out++ = buffer[i % (TC_AES_BLOCK_SIZE)] ^ *in++;
    }

    /* update the counter */
    ctr[14] = nonce[14];
    ctr[15] = nonce[15];
    return TC_CRYPTO_SUCCESS;
}

int tc_ccm_generation_encryption(uint8_t* out, unsigned int olen,
                                 const uint8_t* associated_data,
                                 unsigned int alen, const uint8_t* payload,
                                 unsigned int plen, TCCcmMode_t c)
{
    /* input sanity check: */
    if ((out == (uint8_t*) 0) ||
            (c == (TCCcmMode_t) 0) ||
            ((plen > 0) && (payload == (uint8_t*) 0)) ||
            ((alen > 0) && (associated_data == (uint8_t*) 0)) ||
            (alen >= TC_CCM_AAD_MAX_BYTES) || /* associated data size unsupported */
            (plen >= TC_CCM_PAYLOAD_MAX_BYTES) || /* payload size unsupported */
            (olen < (plen + c->mlen)))    /* invalid output buffer size */
    {
        return TC_CRYPTO_FAIL;
    }

    uint8_t b[Nb * Nk];
    uint8_t tag[Nb * Nk];
    unsigned int i;
    /* GENERATING THE AUTHENTICATION TAG: */
    /* formatting the sequence b for authentication: */
    b[0] = ((alen > 0) ? 0x40:0) | (((c->mlen - 2) / 2 << 3)) | (1);

    for (i = 1; i <= 13; ++i)
    {
        b[i] = c->nonce[i - 1];
    }

    b[14] = (uint8_t)(plen >> 8);
    b[15] = (uint8_t)(plen);
    /* computing the authentication tag using cbc-mac: */
    (void) tc_aes_encrypt(tag, b, c->sched);

    if (alen > 0)
    {
        ccm_cbc_mac(tag, associated_data, alen, 1, c->sched);
    }

    if (plen > 0)
    {
        ccm_cbc_mac(tag, payload, plen, 0, c->sched);
    }

    /* ENCRYPTION: */
    /* formatting the sequence b for encryption: */
    b[0] = 1; /* q - 1 = 2 - 1 = 1 */
    b[14] = b[15] = TC_ZERO_BYTE;
    /* encrypting payload using ctr mode: */
    ccm_ctr_mode(out, plen, payload, plen, b, c->sched);
    b[14] = b[15] = TC_ZERO_BYTE; /* restoring initial counter for ctr_mode (0):*/
    /* encrypting b and adding the tag to the output: */
    (void) tc_aes_encrypt(b, b, c->sched);
    out += plen;

    for (i = 0; i < c->mlen; ++i)
    {
        *out++ = tag[i] ^ b[i];
    }

    return TC_CRYPTO_SUCCESS;
}

int tc_ccm_decryption_verification(uint8_t* out, unsigned int olen,
                                   const uint8_t* associated_data,
                                   unsigned int alen, const uint8_t* payload,
                                   unsigned int plen, TCCcmMode_t c)
{
    /* input sanity check: */
    if ((out == (uint8_t*) 0) ||
            (c == (TCCcmMode_t) 0) ||
            ((plen > 0) && (payload == (uint8_t*) 0)) ||
            ((alen > 0) && (associated_data == (uint8_t*) 0)) ||
            (alen >= TC_CCM_AAD_MAX_BYTES) || /* associated data size unsupported */
            (plen >= TC_CCM_PAYLOAD_MAX_BYTES) || /* payload size unsupported */
            (olen < plen - c->mlen))   /* invalid output buffer size */
    {
        return TC_CRYPTO_FAIL;
    }

    uint8_t b[Nb * Nk];
    uint8_t tag[Nb * Nk];
    unsigned int i;
    /* DECRYPTION: */
    /* formatting the sequence b for decryption: */
    b[0] = 1; /* q - 1 = 2 - 1 = 1 */

    for (i = 1; i < 14; ++i)
    {
        b[i] = c->nonce[i - 1];
    }

    b[14] = b[15] = TC_ZERO_BYTE; /* initial counter value is 0 */
    /* decrypting payload using ctr mode: */
    ccm_ctr_mode(out, plen - c->mlen, payload, plen - c->mlen, b, c->sched);
    b[14] = b[15] = TC_ZERO_BYTE; /* restoring initial counter value (0) */
    /* encrypting b and restoring the tag from input: */
    (void) tc_aes_encrypt(b, b, c->sched);

    for (i = 0; i < c->mlen; ++i)
    {
        tag[i] = *(payload + plen - c->mlen + i) ^ b[i];
    }

    /* VERIFYING THE AUTHENTICATION TAG: */
    /* formatting the sequence b for authentication: */
    b[0] = ((alen > 0) ? 0x40:0)|(((c->mlen - 2) / 2 << 3)) | (1);

    for (i = 1; i < 14; ++i)
    {
        b[i] = c->nonce[i - 1];
    }

    b[14] = (uint8_t)((plen - c->mlen) >> 8);
    b[15] = (uint8_t)(plen - c->mlen);
    /* computing the authentication tag using cbc-mac: */
    (void) tc_aes_encrypt(b, b, c->sched);

    if (alen > 0)
    {
        ccm_cbc_mac(b, associated_data, alen, 1, c->sched);
    }

    if (plen > 0)
    {
        ccm_cbc_mac(b, out, plen - c->mlen, 0, c->sched);
    }

    /* comparing the received tag and the computed one: */
    if (_compare(b, tag, c->mlen) == 0)
    {
        return TC_CRYPTO_SUCCESS;
    }
    else
    {
        /* erase the decrypted buffer in case of mac validation failure: */
        _set(out, 0, plen - c->mlen);
        return TC_CRYPTO_FAIL;
    }
}
