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thirdparty/libtomcrypt/modes/cbc/cbc_decrypt.c

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+/* 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.
+ */
+#include "tomcrypt.h"
+
+/**
+   @file cbc_decrypt.c
+   CBC implementation, encrypt block, Tom St Denis
+*/
+
+
+#ifdef LTC_CBC_MODE
+
+/**
+  CBC decrypt
+  @param ct     Ciphertext
+  @param pt     [out] Plaintext
+  @param len    The number of bytes to process (must be multiple of block length)
+  @param cbc    CBC state
+  @return CRYPT_OK if successful
+*/
+int cbc_decrypt(const unsigned char *ct, unsigned char *pt, unsigned long len, symmetric_CBC *cbc)
+{
+   int x, err;
+   unsigned char tmp[16];
+#ifdef LTC_FAST
+   LTC_FAST_TYPE tmpy;
+#else
+   unsigned char tmpy;
+#endif
+
+   LTC_ARGCHK(pt  != NULL);
+   LTC_ARGCHK(ct  != NULL);
+   LTC_ARGCHK(cbc != NULL);
+
+   if ((err = cipher_is_valid(cbc->cipher)) != CRYPT_OK) {
+       return err;
+   }
+
+   /* is blocklen valid? */
+   if (cbc->blocklen < 1 || cbc->blocklen > (int)sizeof(cbc->IV) || cbc->blocklen > (int)sizeof(tmp)) {
+      return CRYPT_INVALID_ARG;
+   }
+
+   if (len % cbc->blocklen) {
+      return CRYPT_INVALID_ARG;
+   }
+#ifdef LTC_FAST
+   if (cbc->blocklen % sizeof(LTC_FAST_TYPE)) {
+      return CRYPT_INVALID_ARG;
+   }
+#endif
+
+   if (cipher_descriptor[cbc->cipher].accel_cbc_decrypt != NULL) {
+      return cipher_descriptor[cbc->cipher].accel_cbc_decrypt(ct, pt, len / cbc->blocklen, cbc->IV, &cbc->key);
+   } else {
+      while (len) {
+         /* decrypt */
+         if ((err = cipher_descriptor[cbc->cipher].ecb_decrypt(ct, tmp, &cbc->key)) != CRYPT_OK) {
+            return err;
+         }
+
+         /* xor IV against plaintext */
+         #if defined(LTC_FAST)
+         for (x = 0; x < cbc->blocklen; x += sizeof(LTC_FAST_TYPE)) {
+            tmpy = *(LTC_FAST_TYPE_PTR_CAST((unsigned char *)cbc->IV + x)) ^ *(LTC_FAST_TYPE_PTR_CAST((unsigned char *)tmp + x));
+            *(LTC_FAST_TYPE_PTR_CAST((unsigned char *)cbc->IV + x)) = *(LTC_FAST_TYPE_PTR_CAST((unsigned char *)ct + x));
+            *(LTC_FAST_TYPE_PTR_CAST((unsigned char *)pt + x)) = tmpy;
+         }
+    #else
+         for (x = 0; x < cbc->blocklen; x++) {
+            tmpy       = tmp[x] ^ cbc->IV[x];
+            cbc->IV[x] = ct[x];
+            pt[x]      = tmpy;
+         }
+    #endif
+
+         ct  += cbc->blocklen;
+         pt  += cbc->blocklen;
+         len -= cbc->blocklen;
+      }
+   }
+   return CRYPT_OK;
+}
+
+#endif
+
+/* ref:         HEAD -> master, tag: v1.18.2 */
+/* git commit:  7e7eb695d581782f04b24dc444cbfde86af59853 */
+/* commit time: 2018-07-01 22:49:01 +0200 */