cx_aes_siv.c

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/* @BANNER@ */
 
#ifdef HAVE_AES_SIV
#if defined(HAVE_AES) && defined(HAVE_CMAC)
#include "cx_cmac.h"
#include "cx_utils.h"
#include "lcx_cmac.h"
#include "lcx_aes_siv.h"
 
static void cx_clear_bits(uint8_t *input)
{
    input[8] &= 0x7f;
    input[12] &= 0x7f;
}
 
cx_err_t cx_aes_siv_init(cx_aes_siv_context_t *ctx)
{
    cx_err_t error;
    CX_CHECK(cx_cipher_init(ctx->cipher_ctx));
 
end:
    return error;
}
 
cx_err_t cx_aes_siv_set_key(cx_aes_siv_context_t *ctx, const uint8_t *key, size_t key_bitlen)
{
    // AES SIV uses two keys of either 128, 192 or 256 bits each
    if (key_bitlen > AES_SIV_MAX_KEY_LEN * AES_SIV_KEY_NUMBER * 8) {
        return CX_INVALID_PARAMETER_SIZE;
    }
 
    ctx->key_len = key_bitlen / 2;
    memcpy(ctx->key1, key, ctx->key_len / 8);
    memcpy(ctx->key2, key + ctx->key_len / 8, ctx->key_len / 8);
    return CX_OK;
}
 
cx_err_t cx_aes_siv_start(cx_aes_siv_context_t *ctx,
                          uint32_t              mode,
                          const uint8_t        *iv,
                          size_t                iv_len)
{
    uint8_t  iv_used[CX_AES_BLOCK_SIZE] = {0};
    cx_err_t error;
 
    // Set up cipher to be used for CMAC computation
    CX_CHECK(cx_cipher_setup(ctx->cipher_ctx, ctx->cipher_type, CX_CHAIN_ECB));
    CX_CHECK(cx_cmac_start(ctx->cipher_ctx, ctx->key1, ctx->key_len));
    CX_CHECK(cx_cmac_update(ctx->cipher_ctx, iv_used, CX_AES_BLOCK_SIZE));
    CX_CHECK(cx_cmac_finish(ctx->cipher_ctx, ctx->tag_state));
 
    if (CX_DECRYPT == mode) {
        // Prepare for the AES-CTR computation
        memcpy(iv_used, iv, iv_len);
        cx_clear_bits(iv_used);
        CX_CHECK(cx_cipher_setup(ctx->cipher_ctx, ctx->cipher_type, CX_CHAIN_CTR));
        CX_CHECK(cx_cipher_setkey(ctx->cipher_ctx, ctx->key2, ctx->key_len, CX_ENCRYPT));
        CX_CHECK(cx_cipher_setiv(ctx->cipher_ctx, iv_used, CX_AES_BLOCK_SIZE));
    }
    ctx->mode = mode;
 
end:
    return error;
}
 
cx_err_t cx_aes_siv_update_aad(cx_aes_siv_context_t *ctx, const uint8_t *aad, size_t aad_len)
{
    uint8_t  tmp[CX_AES_BLOCK_SIZE] = {0};
    cx_err_t error;
 
    CX_CHECK(cx_cipher_setup(ctx->cipher_ctx, ctx->cipher_type, CX_CHAIN_ECB));
    CX_CHECK(cx_cmac_start(ctx->cipher_ctx, ctx->key1, ctx->key_len));
 
    if (NULL == aad) {
        return CX_OK;
    }
 
    CX_CHECK(cx_cmac_shift_and_xor(tmp, ctx->tag_state, CX_AES_BLOCK_SIZE));
    CX_CHECK(cx_cmac_update(ctx->cipher_ctx, aad, aad_len));
    CX_CHECK(cx_cmac_finish(ctx->cipher_ctx, ctx->tag_state));
    cx_memxor(ctx->tag_state, tmp, CX_AES_BLOCK_SIZE);
    CX_CHECK(cx_cmac_start(ctx->cipher_ctx, ctx->key1, ctx->key_len));
 
end:
    return error;
}
 
cx_err_t cx_aes_siv_update_mac(cx_aes_siv_context_t *ctx, const uint8_t *input, size_t in_len)
{
    return cx_cmac_update(ctx->cipher_ctx, input, in_len);
}
 
cx_err_t cx_aes_siv_update(cx_aes_siv_context_t *ctx,
                           const uint8_t        *input,
                           uint8_t              *output,
                           size_t                len)
{
    size_t   out_len = len;
    cx_err_t error;
    CX_CHECK(cx_cipher_update(ctx->cipher_ctx, input, len, output, &out_len));
 
end:
    return error;
}
 
static cx_err_t cx_aes_siv_check_tag(cx_aes_siv_context_t *ctx, const uint8_t *tag)
{
    uint8_t diff;
    diff = cx_constant_time_eq(tag, ctx->tag_state, CX_AES_BLOCK_SIZE);
    return diff * CX_INVALID_PARAMETER_VALUE + (1 - diff) * CX_OK;
}
 
cx_err_t cx_aes_siv_finish(cx_aes_siv_context_t *ctx,
                           const uint8_t        *input,
                           size_t                in_len,
                           uint8_t              *tag)
{
    uint8_t  tmp[CX_AES_BLOCK_SIZE] = {0};
    cx_err_t error;
 
    if (in_len < CX_AES_BLOCK_SIZE) {
        CX_CHECK(cx_cmac_shift_and_xor(tmp, ctx->tag_state, CX_AES_BLOCK_SIZE));
        memset(ctx->tag_state, 0, CX_AES_BLOCK_SIZE);
        memcpy(ctx->tag_state, input, in_len);
        add_one_and_zeros_padding(ctx->tag_state, CX_AES_BLOCK_SIZE, in_len);
        cx_memxor(tmp, ctx->tag_state, CX_AES_BLOCK_SIZE);
        CX_CHECK(cx_cmac_update(ctx->cipher_ctx, tmp, CX_AES_BLOCK_SIZE));
        CX_CHECK(cx_cmac_finish(ctx->cipher_ctx, ctx->tag_state));
    }
    else {
        CX_CHECK(cx_cmac_update(ctx->cipher_ctx, input, in_len - CX_AES_BLOCK_SIZE));
        cx_memxor(ctx->tag_state, input + in_len - CX_AES_BLOCK_SIZE, CX_AES_BLOCK_SIZE);
        CX_CHECK(cx_cmac_update(ctx->cipher_ctx, ctx->tag_state, CX_AES_BLOCK_SIZE));
        CX_CHECK(cx_cmac_finish(ctx->cipher_ctx, ctx->tag_state));
    }
    if (CX_DECRYPT == ctx->mode) {
        return cx_aes_siv_check_tag(ctx, tag);
    }
    memcpy(tag, ctx->tag_state, CX_AES_BLOCK_SIZE);
    // Prepare for the AES-CTR computation
    cx_clear_bits(ctx->tag_state);
    CX_CHECK(cx_cipher_setup(ctx->cipher_ctx, ctx->cipher_type, CX_CHAIN_CTR));
    CX_CHECK(cx_cipher_setkey(ctx->cipher_ctx, ctx->key2, ctx->key_len, CX_ENCRYPT));
    CX_CHECK(cx_cipher_setiv(ctx->cipher_ctx, ctx->tag_state, CX_AES_BLOCK_SIZE));
 
end:
    return error;
}
 
cx_err_t cx_aes_siv_encrypt(cx_aes_siv_context_t *ctx,
                            const uint8_t        *input,
                            size_t                in_len,
                            const uint8_t        *aad,
                            size_t                aad_len,
                            uint8_t              *output,
                            uint8_t              *tag)
{
    cx_err_t error;
    CX_CHECK(cx_aes_siv_start(ctx, CX_ENCRYPT, NULL, 0));
    CX_CHECK(cx_aes_siv_update_aad(ctx, aad, aad_len));
    CX_CHECK(cx_aes_siv_finish(ctx, input, in_len, tag));
    CX_CHECK(cx_aes_siv_update(ctx, input, output, in_len));
end:
    return error;
}
 
cx_err_t cx_aes_siv_decrypt(cx_aes_siv_context_t *ctx,
                            const uint8_t        *input,
                            size_t                in_len,
                            const uint8_t        *aad,
                            size_t                aad_len,
                            uint8_t              *output,
                            uint8_t              *tag)
{
    cx_err_t error;
    CX_CHECK(cx_aes_siv_start(ctx, CX_DECRYPT, tag, CX_AES_BLOCK_SIZE));
    CX_CHECK(cx_aes_siv_update(ctx, input, output, in_len));
    cx_cipher_reset(ctx->cipher_ctx);
    CX_CHECK(cx_aes_siv_update_aad(ctx, aad, aad_len));
    CX_CHECK(cx_aes_siv_finish(ctx, output, in_len, tag));
 
end:
    return error;
}
 
#endif  // HAVE_AES && HAVE_CMAC
#endif  // HAVE_AES_SIV