Diff: tinydtls/ccm.c

Revision:

0:6ae42a2aff75

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tinydtls/ccm.c	Wed Oct 09 14:48:52 2013 +0000
@@ -0,0 +1,306 @@
+/* dtls -- a very basic DTLS implementation
+ *
+ * Copyright (C) 2011--2012 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 "global.h"
+#include "numeric.h"
+#include "ccm.h"
+
+#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 N[DTLS_CCM_BLOCKSIZE],
+       unsigned char *result) {
+  int i;
+
+  result[0] = CCM_FLAGS(la, M, L);
+
+  /* copy the nonce */
+  memcpy(result + 1, N, 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.
+ */
+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_ulong_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 C;
+
+  SET_COUNTER(A, L, counter, C);    
+  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 N[DTLS_CCM_BLOCKSIZE], 
+			 unsigned char *msg, size_t lm, 
+			 const unsigned char *aad, size_t la) {
+  size_t i, len;
+  unsigned long C;
+  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, N, B);
+  add_auth_data(ctx, aad, la, B, X);
+
+  /* initialize block template */
+  A[0] = L-1;
+
+  /* copy the nonce */
+  memcpy(A + 1, N, 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, C);
+  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 N[DTLS_CCM_BLOCKSIZE], 
+			 unsigned char *msg, size_t lm, 
+			 const unsigned char *aad, size_t la) {
+  
+  size_t len;
+  unsigned long C;
+  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, N, B);
+  add_auth_data(ctx, aad, la, B, X);
+
+  /* initialize block template */
+  A[0] = L-1;
+
+  /* copy the nonce */
+  memcpy(A + 1, N, 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, C);
+  rijndael_encrypt(ctx, A, S);
+
+  memxor(msg, S, M);
+
+  /* return length if MAC is valid, otherwise continue with error handling */
+  if (memcmp(X, msg, M) == 0) 
+    return len - M;
+  
+ error:
+  return -1;
+}