1 files changed, 40 insertions, 1 deletions

diff --git a/aes.c b/aes.c
index 0ff8367..4d240b0 100644
--- a/aes.c
+++ b/aes.c
@@ -1,6 +1,6 @@
 /*
 
-This is an implementation of the AES algorithm, specifically ECB and CBC mode.
+This is an implementation of the AES algorithm, specifically ECB, CTR and CBC mode.
 Block size can be chosen in aes.h - available choices are AES128, AES192, AES256.
 
 The implementation is verified against the test vectors in:
@@ -595,3 +595,42 @@ void AES_CBC_decrypt_buffer(uint8_t* output, uint8_t* input, uint32_t length, co
 }
 
 #endif // #if defined(CBC) && (CBC == 1)
+
+
+
+#if defined(CTR) && (CTR == 1)
+
+void AES_CTR_xcrypt_buffer(uint8_t* output, uint8_t* input, uint32_t length, const uint8_t* key, const uint8_t* iv)
+{
+  uint8_t buffer[BLOCKLEN], counter[BLOCKLEN];
+  
+  memcpy(counter, iv, BLOCKLEN);
+  Key = key;
+  KeyExpansion();
+  
+  int i, j;
+  for (i = 0; i < length; ++i)
+  {
+    if ((i & 0x0F) == 0)
+    {
+      memcpy(buffer, counter, BLOCKLEN);
+      state = (state_t *) buffer;
+      Cipher();
+
+      for (j = (BLOCKLEN - 1); j >= 0; --j)
+      {
+        counter[j] += 1;
+   
+        if (counter[j] != 0)
+        {
+          break;
+        }
+      }
+    }
+
+    output[i] = (input[i]) ^ (buffer[i & 0x0F]);
+  }
+}
+
+#endif // #if defined(CTR) && (CTR == 1)
+