1 files changed, 91 insertions, 0 deletions
diff --git a/libtomcrypt/src/modes/ctr/ctr_start.c b/libtomcrypt/src/modes/ctr/ctr_start.c
new file mode 100644
index 0000000..895c8a4
--- /dev/null
+++ b/libtomcrypt/src/modes/ctr/ctr_start.c
@@ -0,0 +1,91 @@
+/* LibTomCrypt, modular cryptographic library -- Tom St Denis
+ *
+ * LibTomCrypt is a library that provides various cryptographic
+ * algorithms in a highly modular and flexible manner.
+ *
+ * The library is free for all purposes without any express
+ * guarantee it works.
+ *
+ * Tom St Denis, tomstdenis@gmail.com, http://libtomcrypt.com
+ */
+#include "tomcrypt.h"
+
+/**
+   @file ctr_start.c
+   CTR implementation, start chain, Tom St Denis
+*/
+
+
+#ifdef LTC_CTR_MODE
+
+/**
+   Initialize a CTR context
+   @param cipher      The index of the cipher desired
+   @param IV          The initial vector
+   @param key         The secret key 
+   @param keylen      The length of the secret key (octets)
+   @param num_rounds  Number of rounds in the cipher desired (0 for default)
+   @param ctr_mode    The counter mode (CTR_COUNTER_LITTLE_ENDIAN or CTR_COUNTER_BIG_ENDIAN)
+   @param ctr         The CTR state to initialize
+   @return CRYPT_OK if successful
+*/
+int ctr_start(               int   cipher, 
+              const unsigned char *IV, 
+              const unsigned char *key,       int keylen, 
+                             int  num_rounds, int ctr_mode,
+                   symmetric_CTR *ctr)
+{
+   int x, err;
+
+   LTC_ARGCHK(IV  != NULL);
+   LTC_ARGCHK(key != NULL);
+   LTC_ARGCHK(ctr != NULL);
+
+   /* bad param? */
+   if ((err = cipher_is_valid(cipher)) != CRYPT_OK) {
+      return err;
+   }
+
+   /* setup cipher */
+   if ((err = cipher_descriptor[cipher].setup(key, keylen, num_rounds, &ctr->key)) != CRYPT_OK) {
+      return err;
+   }
+
+   /* copy ctr */
+   ctr->blocklen = cipher_descriptor[cipher].block_length;
+   ctr->cipher   = cipher;
+   ctr->padlen   = 0;
+   ctr->mode     = ctr_mode & 1;
+   for (x = 0; x < ctr->blocklen; x++) {
+       ctr->ctr[x] = IV[x];
+   }
+
+   if (ctr_mode & LTC_CTR_RFC3686) {
+      /* increment the IV as per RFC 3686 */
+      if (ctr->mode == CTR_COUNTER_LITTLE_ENDIAN) {
+         /* little-endian */
+         for (x = 0; x < ctr->blocklen; x++) {
+             ctr->ctr[x] = (ctr->ctr[x] + (unsigned char)1) & (unsigned char)255;
+             if (ctr->ctr[x] != (unsigned char)0) {
+                break;
+             }
+         }
+      } else {
+         /* big-endian */
+         for (x = ctr->blocklen-1; x >= 0; x--) {
+             ctr->ctr[x] = (ctr->ctr[x] + (unsigned char)1) & (unsigned char)255;
+             if (ctr->ctr[x] != (unsigned char)0) {
+                break;
+             }
+         }
+      }
+   }
+
+   return cipher_descriptor[ctr->cipher].ecb_encrypt(ctr->ctr, ctr->pad, &ctr->key); 
+}
+
+#endif
+
+/* $Source: /cvs/libtom/libtomcrypt/src/modes/ctr/ctr_start.c,v $ */
+/* $Revision: 1.11 $ */
+/* $Date: 2006/11/05 01:46:35 $ */