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/* ccm.c
 *
 * Counter with CBC-MAC mode, specified by NIST,
 * http://csrc.nist.gov/publications/nistpubs/800-38C/SP800-38C_updated-July20_2007.pdf
 *
 */

/* nettle, low-level cryptographics library
 *
 * Copyright (C) 2014 Exegin Technologies Limited
 * Copyright (C) 2014 Owen Kirby
 *
 * The nettle library is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or (at your
 * option) any later version.
 * 
 * The nettle library is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
 * License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public License
 * along with the nettle library; see the file COPYING.LIB.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
 * MA 02111-1301, USA.
 */

#if HAVE_CONFIG_H
# include "config.h"
#endif

#include <assert.h>
#include <stdlib.h>
#include <string.h>

#include "ccm.h"
#include "ctr.h"

#include "memxor.h"
#include "nettle-internal.h"
#include "macros.h"

/*
 * The format of the CCM IV (for both CTR and CBC-MAC) is: flags | nonce | count
 *  flags = 1 octet
 *  nonce = N octets
 *  count >= 1 octet
 *
 * such that:
 *  sizeof(flags) + sizeof(nonce) + sizeof(count) == 1 block
 */
#define CCM_FLAG_L          0x07
#define CCM_FLAG_M          0x38
#define CCM_FLAG_ADATA      0x40
#define CCM_FLAG_RESERVED   0x80
#define CCM_FLAG_GET_L(_x_) (((_x_) & CCM_FLAG_L) + 1)
#define CCM_FLAG_SET_L(_x_) (((_x_) - 1) & CCM_FLAG_L)
#define CCM_FLAG_SET_M(_x_) ((((_x_) - 2) << 2) & CCM_FLAG_M)

#define CCM_OFFSET_FLAGS    0
#define CCM_OFFSET_NONCE    1
#define CCM_L_SIZE(_nlen_)  (CCM_BLOCK_SIZE - CCM_OFFSET_NONCE - (_nlen_))
#define CCM_L_MAX_SIZE      (CCM_FLAG_L+1)
#define CCM_IV_MAX_SIZE     (CCM_BLOCK_SIZE - CCM_OFFSET_NONCE - 1)
#define CCM_IV_MIN_SIZE     (CCM_BLOCK_SIZE - CCM_OFFSET_NONCE - CCM_L_MAX_SIZE)

/*
 * The data input to the CBC-MAC: L(a) | adata | padding | plaintext | padding
 *
 * blength is the length of data that has been added to the CBC-MAC modulus the
 * cipher block size. If the value of blength is non-zero then some data has
 * been XOR'ed into the CBC-MAC, and we will need to pad the block (XOR with 0),
 * and iterate the cipher one more time.
 *
 * The end of adata is detected implicitly by the first call to the encrypt()
 * and decrypt() functions, and will call ccm_pad() to insert the padding if
 * necessary. Because of the underlying CTR encryption, the encrypt() and
 * decrypt() functions must be called with a multiple of the block size and
 * therefore blength should be zero on all but the first call.
 *
 * Likewise, the end of the plaintext is implicitly determined by the first call
 * to the digest() function, which will pad if the final CTR encryption was not
 * a multiple of the block size.
 */
static void
ccm_pad(struct ccm_ctx *ctx, const void *cipher, nettle_cipher_func *f)
{
    if (ctx->blength) f(cipher, CCM_BLOCK_SIZE, ctx->tag.b, ctx->tag.b);
    ctx->blength = 0;
}

static void
ccm_build_iv(uint8_t *iv, size_t noncelen, const uint8_t *nonce,
	     uint8_t flags, size_t count)
{
  unsigned int i;

  /* Sanity check the nonce length. */
  assert(noncelen >= CCM_IV_MIN_SIZE);
  assert(noncelen <= CCM_IV_MAX_SIZE);

  /* Generate the IV */
  iv[CCM_OFFSET_FLAGS] = flags | CCM_FLAG_SET_L(CCM_L_SIZE(noncelen));
  memcpy(&iv[CCM_OFFSET_NONCE], nonce, noncelen);
  for (i=(CCM_BLOCK_SIZE - 1); i >= (CCM_OFFSET_NONCE + noncelen); i--) {
    iv[i] = count & 0xff;
    count >>= 8;
  }

  /* Ensure the count was not truncated. */
  assert(!count);
}

void
ccm_set_nonce(struct ccm_ctx *ctx, const void *cipher, nettle_cipher_func *f,
	      size_t length, const uint8_t *nonce,
	      size_t authlen, size_t msglen, size_t taglen)
{
  /* Generate the IV for the CTR and CBC-MAC */
  ctx->blength = 0;
  ccm_build_iv(ctx->tag.b, length, nonce, CCM_FLAG_SET_M(taglen), msglen);
  ccm_build_iv(ctx->ctr.b, length, nonce, 0, 1);

  /* If no auth data, encrypt B0 and skip L(a) */
  if (!authlen) {
    f(cipher, CCM_BLOCK_SIZE, ctx->tag.b, ctx->tag.b);
    return;
  }

  /* Encrypt B0 (with the adata flag), and input L(a) to the CBC-MAC. */
  ctx->tag.b[CCM_OFFSET_FLAGS] |= CCM_FLAG_ADATA;
  f(cipher, CCM_BLOCK_SIZE, ctx->tag.b, ctx->tag.b);
  if (authlen >= (0x01ULL << 32)) {
    /* Encode L(a) as 0xff || 0xff || <64-bit integer> */
    ctx->tag.b[ctx->blength++] ^= 0xff;
    ctx->tag.b[ctx->blength++] ^= 0xff;
    ctx->tag.b[ctx->blength++] ^= (authlen >> 56) & 0xff;
    ctx->tag.b[ctx->blength++] ^= (authlen >> 48) & 0xff;
    ctx->tag.b[ctx->blength++] ^= (authlen >> 40) & 0xff;
    ctx->tag.b[ctx->blength++] ^= (authlen >> 32) & 0xff;
    ctx->tag.b[ctx->blength++] ^= (authlen >> 24) & 0xff;
    ctx->tag.b[ctx->blength++] ^= (authlen >> 16) & 0xff;
  }
  else if (authlen >= ((0x1ULL << 16) - (0x1ULL << 8))) {
    /* Encode L(a) as 0xff || 0xfe || <32-bit integer> */
    ctx->tag.b[ctx->blength++] ^= 0xff;
    ctx->tag.b[ctx->blength++] ^= 0xfe;
    ctx->tag.b[ctx->blength++] ^= (authlen >> 24) & 0xff;
    ctx->tag.b[ctx->blength++] ^= (authlen >> 16) & 0xff;
  }
  ctx->tag.b[ctx->blength++] ^= (authlen >> 8) & 0xff;
  ctx->tag.b[ctx->blength++] ^= (authlen >> 0) & 0xff;
}

void
ccm_update(struct ccm_ctx *ctx, const void *cipher, nettle_cipher_func *f,
	   size_t length, const uint8_t *data)
{
  const uint8_t *end = data + length;

  /* If we don't have enough to fill a block, save the data for later. */
  if ((ctx->blength + length) < CCM_BLOCK_SIZE) {
    memxor(&ctx->tag.b[ctx->blength], data, length);
    ctx->blength += length;
    return;
  }

  /* Process a partially filled block. */
  if (ctx->blength) {
    memxor(&ctx->tag.b[ctx->blength], data, CCM_BLOCK_SIZE - ctx->blength);
    data += (CCM_BLOCK_SIZE - ctx->blength);
    f(cipher, CCM_BLOCK_SIZE, ctx->tag.b, ctx->tag.b);
  }

  /* Process full blocks. */
  while ((data + CCM_BLOCK_SIZE) < end) {
    memxor(ctx->tag.b, data, CCM_BLOCK_SIZE);
    f(cipher, CCM_BLOCK_SIZE, ctx->tag.b, ctx->tag.b);
    data += CCM_BLOCK_SIZE;
  } /* while */

  /* Save leftovers for later. */
  ctx->blength = (end - data);
  if (ctx->blength) memxor(&ctx->tag.b, data, ctx->blength);
}

/*
 * Because of the underlying CTR mode encryption, when called multiple times
 * the data in intermediate calls must be provided in multiples of the block
 * size.
 */
void
ccm_encrypt(struct ccm_ctx *ctx, const void *cipher, nettle_cipher_func *f,
	    size_t length, uint8_t *dst, const uint8_t *src)
{
  ccm_pad(ctx, cipher, f);
  ccm_update(ctx, cipher, f, length, src);
  ctr_crypt(cipher, f, CCM_BLOCK_SIZE, ctx->ctr.b, length, dst, src);
}

/*
 * Because of the underlying CTR mode decryption, when called multiple times
 * the data in intermediate calls must be provided in multiples of the block
 * size.
 */
void
ccm_decrypt(struct ccm_ctx *ctx, const void *cipher, nettle_cipher_func *f,
	    size_t length, uint8_t *dst, const uint8_t *src)
{
  ctr_crypt(cipher, f, CCM_BLOCK_SIZE, ctx->ctr.b, length, dst, src);
  ccm_pad(ctx, cipher, f);
  ccm_update(ctx, cipher, f, length, dst);
}

void
ccm_digest(struct ccm_ctx *ctx, const void *cipher, nettle_cipher_func *f,
	   size_t length, uint8_t *digest)
{
  int i = CCM_BLOCK_SIZE - CCM_FLAG_GET_L(ctx->ctr.b[CCM_OFFSET_FLAGS]);
  assert(length <= CCM_BLOCK_SIZE);
  while (i < CCM_BLOCK_SIZE)  ctx->ctr.b[i++] = 0;
  ccm_pad(ctx, cipher, f);
  ctr_crypt(cipher, f, CCM_BLOCK_SIZE, ctx->ctr.b, length, digest, ctx->tag.b);
}

void
ccm_encrypt_message(const void *cipher, nettle_cipher_func *f,
		    size_t nlength, const uint8_t *nonce,
		    size_t alength, const uint8_t *adata, size_t tlength,
		    size_t clength, uint8_t *dst, const uint8_t *src)
{
  struct ccm_ctx ctx;
  uint8_t *tag = dst + (clength-tlength);
  assert(clength >= tlength);
  ccm_set_nonce(&ctx, cipher, f, nlength, nonce, alength, clength-tlength, tlength);
  ccm_update(&ctx, cipher, f, alength, adata);
  ccm_encrypt(&ctx, cipher, f, clength-tlength, dst, src);
  ccm_digest(&ctx, cipher, f, tlength, tag);
}

int
ccm_decrypt_message(const void *cipher, nettle_cipher_func *f,
		    size_t nlength, const uint8_t *nonce,
		    size_t alength, const uint8_t *adata, size_t tlength,
		    size_t clength, uint8_t *dst, const uint8_t *src)
{
  struct ccm_ctx ctx;
  uint8_t tag[CCM_BLOCK_SIZE];
  assert(clength >= tlength);
  ccm_set_nonce(&ctx, cipher, f, nlength, nonce, alength, clength-tlength, tlength);
  ccm_update(&ctx, cipher, f, alength, adata);
  ccm_decrypt(&ctx, cipher, f, clength-tlength, dst, src);
  ccm_digest(&ctx, cipher, f, tlength, tag);
  return (memcmp(tag, src + (clength-tlength), tlength) == 0);
}