/*      $OpenBSD: cmac.c,v 1.3 2017/05/02 17:07:06 mikeb Exp $  */

/*-
 * Copyright (c) 2008 Damien Bergamini <damien.bergamini@free.fr>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

/*
 * This code implements the CMAC (Cipher-based Message Authentication)
 * algorithm described in FIPS SP800-38B using the AES-128 cipher.
 */

#include <sys/param.h>
#include <sys/systm.h>

#include <crypto/aes.h>
#include <crypto/cmac.h>

#define LSHIFT(v, r) do {                                       \
        int i;                                                  \
        for (i = 0; i < 15; i++)                                \
                (r)[i] = (v)[i] << 1 | (v)[i + 1] >> 7;         \
        (r)[15] = (v)[15] << 1;                                 \
} while (0)

#define XOR(v, r) do {                                          \
        int i;                                                  \
        for (i = 0; i < 16; i++)                                \
                (r)[i] ^= (v)[i];                               \
} while (0)

void
AES_CMAC_Init(AES_CMAC_CTX *ctx)
{
        memset(ctx->X, 0, sizeof ctx->X);
        ctx->M_n = 0;
}

void
AES_CMAC_SetKey(AES_CMAC_CTX *ctx, const u_int8_t key[AES_CMAC_KEY_LENGTH])
{
        AES_Setkey(&ctx->aesctx, key, 16);
}

void
AES_CMAC_Update(AES_CMAC_CTX *ctx, const u_int8_t *data, u_int len)
{
        u_int mlen;

        if (ctx->M_n > 0) {
                mlen = MIN(16 - ctx->M_n, len);
                memcpy(ctx->M_last + ctx->M_n, data, mlen);
                ctx->M_n += mlen;
                if (ctx->M_n < 16 || len == mlen)
                        return;
                XOR(ctx->M_last, ctx->X);
                AES_Encrypt(&ctx->aesctx, ctx->X, ctx->X);
                data += mlen;
                len -= mlen;
        }
        while (len > 16) {      /* not last block */
                XOR(data, ctx->X);
                AES_Encrypt(&ctx->aesctx, ctx->X, ctx->X);
                data += 16;
                len -= 16;
        }
        /* potential last block, save it */
        memcpy(ctx->M_last, data, len);
        ctx->M_n = len;
}

void
AES_CMAC_Final(u_int8_t digest[AES_CMAC_DIGEST_LENGTH], AES_CMAC_CTX *ctx)
{
        u_int8_t K[16];

        /* generate subkey K1 */
        memset(K, 0, sizeof K);
        AES_Encrypt(&ctx->aesctx, K, K);

        if (K[0] & 0x80) {
                LSHIFT(K, K);
                K[15] ^= 0x87;
        } else
                LSHIFT(K, K);

        if (ctx->M_n == 16) {
                /* last block was a complete block */
                XOR(K, ctx->M_last);
        } else {
                /* generate subkey K2 */
                if (K[0] & 0x80) {
                        LSHIFT(K, K);
                        K[15] ^= 0x87;
                } else
                        LSHIFT(K, K);

                /* padding(M_last) */
                ctx->M_last[ctx->M_n] = 0x80;
                while (++ctx->M_n < 16)
                        ctx->M_last[ctx->M_n] = 0;

                XOR(K, ctx->M_last);
        }
        XOR(ctx->M_last, ctx->X);
        AES_Encrypt(&ctx->aesctx, ctx->X, digest);

        explicit_bzero(K, sizeof K);
}