/* $OpenBSD: cmac.c,v 1.24 2024/05/20 14:53:37 tb Exp $ */

/* Written by Dr Stephen N Henson (steve@openssl.org) for the OpenSSL

 * project.

 */

/* ====================================================================

 * Copyright (c) 2010 The OpenSSL Project.  All rights reserved.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 *

 * 1. Redistributions of source code must retain the above copyright

 *    notice, this list of conditions and the following disclaimer.

 *

 * 2. Redistributions in binary form must reproduce the above copyright

 *    notice, this list of conditions and the following disclaimer in

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 *    distribution.

 *

 * 3. All advertising materials mentioning features or use of this

 *    software must display the following acknowledgment:

 *    "This product includes software developed by the OpenSSL Project

 *    for use in the OpenSSL Toolkit. (http://www.OpenSSL.org/)"

 *

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 *    licensing@OpenSSL.org.

 *

 * 5. Products derived from this software may not be called "OpenSSL"

 *    nor may "OpenSSL" appear in their names without prior written

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 *    acknowledgment:

 *    "This product includes software developed by the OpenSSL Project

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 *

 * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY

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#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <openssl/cmac.h>

#include "evp_local.h"

/*

 * This implementation follows https://doi.org/10.6028/NIST.SP.800-38B

 */

/*

 * CMAC context. k1 and k2 are the secret subkeys, computed as in section 6.1.

 * The temporary block tbl is a scratch buffer that holds intermediate secrets.

 */

struct CMAC_CTX_st {

  EVP_CIPHER_CTX *cipher_ctx;

  unsigned char k1[EVP_MAX_BLOCK_LENGTH];

  unsigned char k2[EVP_MAX_BLOCK_LENGTH];

  unsigned char tbl[EVP_MAX_BLOCK_LENGTH];

  unsigned char last_block[EVP_MAX_BLOCK_LENGTH];

  /* Bytes in last block. -1 means not initialized. */

  int nlast_block;

};

/*

 * SP 800-38B, section 6.1, steps 2 and 3: given the input key l, calculate

 * the subkeys k1 and k2: shift l one bit to the left. If the most significant

 * bit of l was 1, additionally xor the result with Rb to get kn.

 *

 * Step 2: calculate k1 with l being the intermediate block CIPH_K(0),

 * Step 3: calculate k2 from l == k1.

 *

 * Per 5.3, Rb is the lexically first irreducible polynomial of degree b with

 * the minimum number of non-zero terms. This gives R128 = (1 << 128) | 0x87

 * and R64 = (1 << 64) | 0x1b for the only supported block sizes 128 and 64.

 */

static void

make_kn(unsigned char *kn, const unsigned char *l, int block_size)

{

  unsigned char mask, Rb;

  int i;

  /* Choose Rb according to the block size in bytes. */

  Rb = block_size == 16 ? 0x87 : 0x1b;

  /* Compute l << 1 up to last byte. */

  for (i = 0; i < block_size - 1; i++)

    kn[i] = (l[i] << 1) | (l[i + 1] >> 7);

  /* Only xor with Rb if the MSB is one. */

  mask = 0 - (l[0] >> 7);

  kn[block_size - 1] = (l[block_size - 1] << 1) ^ (Rb & mask);

}

CMAC_CTX *

CMAC_CTX_new(void)

{

  CMAC_CTX *ctx;

  if ((ctx = calloc(1, sizeof(CMAC_CTX))) == NULL)

    goto err;

  if ((ctx->cipher_ctx = EVP_CIPHER_CTX_new()) == NULL)

    goto err;

  ctx->nlast_block = -1;

  return ctx;

 err:

  CMAC_CTX_free(ctx);

  return NULL;

}

LCRYPTO_ALIAS(CMAC_CTX_new);

void

CMAC_CTX_cleanup(CMAC_CTX *ctx)

{

  (void)EVP_CIPHER_CTX_reset(ctx->cipher_ctx);

  explicit_bzero(ctx->tbl, EVP_MAX_BLOCK_LENGTH);

  explicit_bzero(ctx->k1, EVP_MAX_BLOCK_LENGTH);

  explicit_bzero(ctx->k2, EVP_MAX_BLOCK_LENGTH);

  explicit_bzero(ctx->last_block, EVP_MAX_BLOCK_LENGTH);

  ctx->nlast_block = -1;

}

LCRYPTO_ALIAS(CMAC_CTX_cleanup);

EVP_CIPHER_CTX *

CMAC_CTX_get0_cipher_ctx(CMAC_CTX *ctx)

{

  return ctx->cipher_ctx;

}

LCRYPTO_ALIAS(CMAC_CTX_get0_cipher_ctx);

void

CMAC_CTX_free(CMAC_CTX *ctx)

{

  if (ctx == NULL)

    return;

  CMAC_CTX_cleanup(ctx);

  EVP_CIPHER_CTX_free(ctx->cipher_ctx);

  freezero(ctx, sizeof(CMAC_CTX));

}

LCRYPTO_ALIAS(CMAC_CTX_free);

int

CMAC_CTX_copy(CMAC_CTX *out, const CMAC_CTX *in)

{

  int block_size;

  if (in->nlast_block == -1)

    return 0;

  if (!EVP_CIPHER_CTX_copy(out->cipher_ctx, in->cipher_ctx))

    return 0;

  block_size = EVP_CIPHER_CTX_block_size(in->cipher_ctx);

  memcpy(out->k1, in->k1, block_size);

  memcpy(out->k2, in->k2, block_size);

  memcpy(out->tbl, in->tbl, block_size);

  memcpy(out->last_block, in->last_block, block_size);

  out->nlast_block = in->nlast_block;

  return 1;

}

LCRYPTO_ALIAS(CMAC_CTX_copy);

int

CMAC_Init(CMAC_CTX *ctx, const void *key, size_t keylen,

    const EVP_CIPHER *cipher, ENGINE *impl)

{

  static const unsigned char zero_iv[EVP_MAX_BLOCK_LENGTH];

  int block_size;

  /* All zeros means restart */

  if (key == NULL && cipher == NULL && keylen == 0) {

    /* Not initialised */

    if (ctx->nlast_block == -1)

      return 0;

    if (!EVP_EncryptInit_ex(ctx->cipher_ctx, NULL, NULL, NULL, zero_iv))

      return 0;

    explicit_bzero(ctx->tbl, sizeof(ctx->tbl));

    ctx->nlast_block = 0;

    return 1;

  }

  /* Initialise context. */

  if (cipher != NULL) {

    /*

     * Disallow ciphers for which EVP_Cipher() behaves differently.

     * These are AEAD ciphers (or AES keywrap) for which the CMAC

     * construction makes little sense.

     */

    if ((cipher->flags & EVP_CIPH_FLAG_CUSTOM_CIPHER) != 0)

      return 0;

    if (!EVP_EncryptInit_ex(ctx->cipher_ctx, cipher, NULL, NULL, NULL))

      return 0;

  }

  /* Non-NULL key means initialisation is complete. */

  if (key != NULL) {

    if (EVP_CIPHER_CTX_cipher(ctx->cipher_ctx) == NULL)

      return 0;

    /* make_kn() only supports block sizes of 8 and 16 bytes. */

    block_size = EVP_CIPHER_CTX_block_size(ctx->cipher_ctx);

    if (block_size != 8 && block_size != 16)

      return 0;

    /*

     * Section 6.1, step 1: store the intermediate secret CIPH_K(0)

     * in ctx->tbl.

     */

    if (!EVP_CIPHER_CTX_set_key_length(ctx->cipher_ctx, keylen))

      return 0;

    if (!EVP_EncryptInit_ex(ctx->cipher_ctx, NULL, NULL, key, zero_iv))

      return 0;

    if (!EVP_Cipher(ctx->cipher_ctx, ctx->tbl, zero_iv, block_size))

      return 0;

    /* Section 6.1, step 2: compute k1 from intermediate secret. */

    make_kn(ctx->k1, ctx->tbl, block_size);

    /* Section 6.1, step 3: compute k2 from k1. */

    make_kn(ctx->k2, ctx->k1, block_size);

    /* Destroy intermediate secret and reset last block count. */

    explicit_bzero(ctx->tbl, sizeof(ctx->tbl));

    ctx->nlast_block = 0;

    /* Reset context again to get ready for the first data block. */

    if (!EVP_EncryptInit_ex(ctx->cipher_ctx, NULL, NULL, NULL, zero_iv))

      return 0;

  }

  return 1;

}

LCRYPTO_ALIAS(CMAC_Init);

int

CMAC_Update(CMAC_CTX *ctx, const void *in, size_t dlen)

{

  const unsigned char *data = in;

  size_t block_size;

  if (ctx->nlast_block == -1)

    return 0;

  if (dlen == 0)

    return 1;

  block_size = EVP_CIPHER_CTX_block_size(ctx->cipher_ctx);

  /* Copy into partial block if we need to */

  if (ctx->nlast_block > 0) {

    size_t nleft;

    nleft = block_size - ctx->nlast_block;

    if (dlen < nleft)

      nleft = dlen;

    memcpy(ctx->last_block + ctx->nlast_block, data, nleft);

    dlen -= nleft;

    ctx->nlast_block += nleft;

    /* If no more to process return */

    if (dlen == 0)

      return 1;

    data += nleft;

    /* Else not final block so encrypt it */

    if (!EVP_Cipher(ctx->cipher_ctx, ctx->tbl, ctx->last_block,

        block_size))

      return 0;

  }

  /* Encrypt all but one of the complete blocks left */

  while (dlen > block_size) {

    if (!EVP_Cipher(ctx->cipher_ctx, ctx->tbl, data, block_size))

      return 0;

    dlen -= block_size;

    data += block_size;

  }

  /* Copy any data left to last block buffer */

  memcpy(ctx->last_block, data, dlen);

  ctx->nlast_block = dlen;

  return 1;

}

LCRYPTO_ALIAS(CMAC_Update);

int

CMAC_Final(CMAC_CTX *ctx, unsigned char *out, size_t *poutlen)

{

  int i, block_size, lb;

  if (ctx->nlast_block == -1)

    return 0;

  block_size = EVP_CIPHER_CTX_block_size(ctx->cipher_ctx);

  *poutlen = (size_t)block_size;

  if (!out)

    return 1;

  lb = ctx->nlast_block;

  /* Is last block complete? */

  if (lb == block_size) {

    for (i = 0; i < block_size; i++)

      out[i] = ctx->last_block[i] ^ ctx->k1[i];

  } else {

    ctx->last_block[lb] = 0x80;

    if (block_size - lb > 1)

      memset(ctx->last_block + lb + 1, 0, block_size - lb - 1);

    for (i = 0; i < block_size; i++)

      out[i] = ctx->last_block[i] ^ ctx->k2[i];

  }

  if (!EVP_Cipher(ctx->cipher_ctx, out, out, block_size)) {

    explicit_bzero(out, block_size);

    return 0;

  }

  return 1;

}

LCRYPTO_ALIAS(CMAC_Final);