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tinydtls-ccm.c
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tinydtls-ccm.c
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/* dtls -- a very basic DTLS implementation
*
* Copyright (C) 2011--2014 Olaf Bergmann <bergmann@tzi.org>
*
* Permission is hereby granted, free of charge, to any person
* obtaining a copy of this software and associated documentation
* files (the "Software"), to deal in the Software without
* restriction, including without limitation the rights to use, copy,
* modify, merge, publish, distribute, sublicense, and/or sell copies
* of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
#include <string.h>
#include "dtls_config.h"
#include "global.h"
#include "numeric.h"
#include "tinydtls-ccm.h"
#ifdef HAVE_ASSERT_H
# include <assert.h>
#endif
#define CCM_FLAGS(A,M,L) (((A > 0) << 6) | (((M - 2)/2) << 3) | (L - 1))
#define MASK_L(_L) ((1 << 8 * _L) - 1)
#define SET_COUNTER(A,L,cnt,C) { \
int i; \
memset((A) + DTLS_CCM_BLOCKSIZE - (L), 0, (L)); \
(C) = (cnt) & MASK_L(L); \
for (i = DTLS_CCM_BLOCKSIZE - 1; (C) && (i > (L)); --i, (C) >>= 8) \
(A)[i] |= (C) & 0xFF; \
}
static inline void
block0(size_t M, /* number of auth bytes */
size_t L, /* number of bytes to encode message length */
size_t la, /* l(a) octets additional authenticated data */
size_t lm, /* l(m) message length */
unsigned char nonce[DTLS_CCM_BLOCKSIZE],
unsigned char *result) {
int i;
result[0] = CCM_FLAGS(la, M, L);
/* copy the nonce */
memcpy(result + 1, nonce, DTLS_CCM_BLOCKSIZE - L);
for (i=0; i < L; i++) {
result[15-i] = lm & 0xff;
lm >>= 8;
}
}
/**
* Creates the CBC-MAC for the additional authentication data that
* is sent in cleartext.
*
* \param ctx The crypto context for the AES encryption.
* \param msg The message starting with the additional authentication data.
* \param la The number of additional authentication bytes in \p msg.
* \param B The input buffer for crypto operations. When this function
* is called, \p B must be initialized with \c B0 (the first
* authentication block.
* \param X The output buffer where the result of the CBC calculation
* is placed.
* \return The result is written to \p X.
*/
static void
add_auth_data(rijndael_ctx *ctx, const unsigned char *msg, size_t la,
unsigned char B[DTLS_CCM_BLOCKSIZE],
unsigned char X[DTLS_CCM_BLOCKSIZE]) {
size_t i,j;
rijndael_encrypt(ctx, B, X);
memset(B, 0, DTLS_CCM_BLOCKSIZE);
if (!la)
return;
#ifndef WITH_CONTIKI
if (la < 0xFF00) { /* 2^16 - 2^8 */
j = 2;
dtls_int_to_uint16(B, la);
} else if (la <= UINT32_MAX) {
j = 6;
dtls_int_to_uint16(B, 0xFFFE);
dtls_int_to_uint32(B+2, la);
} else {
j = 10;
dtls_int_to_uint16(B, 0xFFFF);
dtls_int_to_uint64(B+2, la);
}
#else /* WITH_CONTIKI */
/* With Contiki, we are building for small devices and thus
* anticipate that the number of additional authentication bytes
* will not exceed 65280 bytes (0xFF00) and we can skip the
* workarounds required for j=6 and j=10 on devices with a word size
* of 32 bits or 64 bits, respectively.
*/
assert(la < 0xFF00);
j = 2;
dtls_int_to_uint16(B, la);
#endif /* WITH_CONTIKI */
i = min(DTLS_CCM_BLOCKSIZE - j, la);
memcpy(B + j, msg, i);
la -= i;
msg += i;
memxor(B, X, DTLS_CCM_BLOCKSIZE);
rijndael_encrypt(ctx, B, X);
while (la > DTLS_CCM_BLOCKSIZE) {
for (i = 0; i < DTLS_CCM_BLOCKSIZE; ++i)
B[i] = X[i] ^ *msg++;
la -= DTLS_CCM_BLOCKSIZE;
rijndael_encrypt(ctx, B, X);
}
if (la) {
memset(B, 0, DTLS_CCM_BLOCKSIZE);
memcpy(B, msg, la);
memxor(B, X, DTLS_CCM_BLOCKSIZE);
rijndael_encrypt(ctx, B, X);
}
}
static inline void
encrypt(rijndael_ctx *ctx, size_t L, unsigned long counter,
unsigned char *msg, size_t len,
unsigned char A[DTLS_CCM_BLOCKSIZE],
unsigned char S[DTLS_CCM_BLOCKSIZE]) {
static unsigned long counter_tmp;
SET_COUNTER(A, L, counter, counter_tmp);
rijndael_encrypt(ctx, A, S);
memxor(msg, S, len);
}
static inline void
mac(rijndael_ctx *ctx,
unsigned char *msg, size_t len,
unsigned char B[DTLS_CCM_BLOCKSIZE],
unsigned char X[DTLS_CCM_BLOCKSIZE]) {
size_t i;
for (i = 0; i < len; ++i)
B[i] = X[i] ^ msg[i];
rijndael_encrypt(ctx, B, X);
}
long int
dtls_ccm_encrypt_message(rijndael_ctx *ctx, size_t M, size_t L,
unsigned char nonce[DTLS_CCM_BLOCKSIZE],
unsigned char *msg, size_t lm,
const unsigned char *aad, size_t la) {
size_t i, len;
unsigned long counter_tmp;
unsigned long counter = 1; /* \bug does not work correctly on ia32 when
lm >= 2^16 */
unsigned char A[DTLS_CCM_BLOCKSIZE]; /* A_i blocks for encryption input */
unsigned char B[DTLS_CCM_BLOCKSIZE]; /* B_i blocks for CBC-MAC input */
unsigned char S[DTLS_CCM_BLOCKSIZE]; /* S_i = encrypted A_i blocks */
unsigned char X[DTLS_CCM_BLOCKSIZE]; /* X_i = encrypted B_i blocks */
len = lm; /* save original length */
/* create the initial authentication block B0 */
block0(M, L, la, lm, nonce, B);
add_auth_data(ctx, aad, la, B, X);
/* initialize block template */
A[0] = L-1;
/* copy the nonce */
memcpy(A + 1, nonce, DTLS_CCM_BLOCKSIZE - L);
while (lm >= DTLS_CCM_BLOCKSIZE) {
/* calculate MAC */
mac(ctx, msg, DTLS_CCM_BLOCKSIZE, B, X);
/* encrypt */
encrypt(ctx, L, counter, msg, DTLS_CCM_BLOCKSIZE, A, S);
/* update local pointers */
lm -= DTLS_CCM_BLOCKSIZE;
msg += DTLS_CCM_BLOCKSIZE;
counter++;
}
if (lm) {
/* Calculate MAC. The remainder of B must be padded with zeroes, so
* B is constructed to contain X ^ msg for the first lm bytes (done in
* mac() and X ^ 0 for the remaining DTLS_CCM_BLOCKSIZE - lm bytes
* (i.e., we can use memcpy() here).
*/
memcpy(B + lm, X + lm, DTLS_CCM_BLOCKSIZE - lm);
mac(ctx, msg, lm, B, X);
/* encrypt */
encrypt(ctx, L, counter, msg, lm, A, S);
/* update local pointers */
msg += lm;
}
/* calculate S_0 */
SET_COUNTER(A, L, 0, counter_tmp);
rijndael_encrypt(ctx, A, S);
for (i = 0; i < M; ++i)
*msg++ = X[i] ^ S[i];
return len + M;
}
long int
dtls_ccm_decrypt_message(rijndael_ctx *ctx, size_t M, size_t L,
unsigned char nonce[DTLS_CCM_BLOCKSIZE],
unsigned char *msg, size_t lm,
const unsigned char *aad, size_t la) {
size_t len;
unsigned long counter_tmp;
unsigned long counter = 1; /* \bug does not work correctly on ia32 when
lm >= 2^16 */
unsigned char A[DTLS_CCM_BLOCKSIZE]; /* A_i blocks for encryption input */
unsigned char B[DTLS_CCM_BLOCKSIZE]; /* B_i blocks for CBC-MAC input */
unsigned char S[DTLS_CCM_BLOCKSIZE]; /* S_i = encrypted A_i blocks */
unsigned char X[DTLS_CCM_BLOCKSIZE]; /* X_i = encrypted B_i blocks */
if (lm < M)
goto error;
len = lm; /* save original length */
lm -= M; /* detract MAC size*/
/* create the initial authentication block B0 */
block0(M, L, la, lm, nonce, B);
add_auth_data(ctx, aad, la, B, X);
/* initialize block template */
A[0] = L-1;
/* copy the nonce */
memcpy(A + 1, nonce, DTLS_CCM_BLOCKSIZE - L);
while (lm >= DTLS_CCM_BLOCKSIZE) {
/* decrypt */
encrypt(ctx, L, counter, msg, DTLS_CCM_BLOCKSIZE, A, S);
/* calculate MAC */
mac(ctx, msg, DTLS_CCM_BLOCKSIZE, B, X);
/* update local pointers */
lm -= DTLS_CCM_BLOCKSIZE;
msg += DTLS_CCM_BLOCKSIZE;
counter++;
}
if (lm) {
/* decrypt */
encrypt(ctx, L, counter, msg, lm, A, S);
/* Calculate MAC. Note that msg ends in the MAC so we must
* construct B to contain X ^ msg for the first lm bytes (done in
* mac() and X ^ 0 for the remaining DTLS_CCM_BLOCKSIZE - lm bytes
* (i.e., we can use memcpy() here).
*/
memcpy(B + lm, X + lm, DTLS_CCM_BLOCKSIZE - lm);
mac(ctx, msg, lm, B, X);
/* update local pointers */
msg += lm;
}
/* calculate S_0 */
SET_COUNTER(A, L, 0, counter_tmp);
rijndael_encrypt(ctx, A, S);
memxor(msg, S, M);
/* return length if MAC is valid, otherwise continue with error handling */
if (equals(X, msg, M))
return len - M;
error:
return -1;
}