avutil/aes_ctr: Add method to set 16-byte IV.

Signed-off-by: Jacob Trimble <modmaker@google.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

doc/APIchanges

@@ -15,6 +15,9 @@ libavutil:     2017-10-21
 
 API changes, most recent first:
 
+2018-xx-xx - xxxxxxx - lavu 56.9.100 - aes_ctr.h
+  Add method to set the 16-byte IV.
+
 2018-01-xx - xxxxxxx - lavf 58.5.100 - avformat.h
   Explicitly make avformat_network_init() and avformat_network_deinit() optional.
   If these are not called, network initialization and deinitialization is

libavutil/aes_ctr.c

@@ -45,6 +45,12 @@ void av_aes_ctr_set_iv(struct AVAESCTR *a, const uint8_t* iv)
     a->block_offset = 0;
 }
 
+void av_aes_ctr_set_full_iv(struct AVAESCTR *a, const uint8_t* iv)
+{
+    memcpy(a->counter, iv, sizeof(a->counter));
+    a->block_offset = 0;
+}
+
 const uint8_t* av_aes_ctr_get_iv(struct AVAESCTR *a)
 {
     return a->counter;

libavutil/aes_ctr.h

@@ -67,10 +67,15 @@ const uint8_t* av_aes_ctr_get_iv(struct AVAESCTR *a);
 void av_aes_ctr_set_random_iv(struct AVAESCTR *a);
 
 /**
- * Forcefully change the iv
+ * Forcefully change the 8-byte iv
  */
 void av_aes_ctr_set_iv(struct AVAESCTR *a, const uint8_t* iv);
 
+/**
+ * Forcefully change the "full" 16-byte iv, including the counter
+ */
+void av_aes_ctr_set_full_iv(struct AVAESCTR *a, const uint8_t* iv);
+
 /**
  * Increment the top 64 bit of the iv (performed after each frame)
  */

libavutil/tests/aes_ctr.c

@@ -45,7 +45,7 @@ int main (void)
 
     av_aes_ctr_set_random_iv(ae);
     iv =   av_aes_ctr_get_iv(ae);
-    av_aes_ctr_set_iv(ad, iv);
+    av_aes_ctr_set_full_iv(ad, iv);
 
     av_aes_ctr_crypt(ae, tmp, plain, sizeof(tmp));
     av_aes_ctr_crypt(ad, tmp, tmp,   sizeof(tmp));