chacha_crypt: Fixed block counter update.

ChangeLog

+2014-02-08  Niels Möller  <nisse@lysator.liu.se>
+
+	* chacha-crypt.c (chacha_crypt): Fixed block counter update.
+
 2014-02-07  Niels Möller  <nisse@lysator.liu.se>
 
 	* nettle.texinfo (ASCII encoding): Document that

chacha-crypt.c

@@ -60,7 +60,7 @@ chacha_crypt(struct chacha_ctx *ctx,
 
       _chacha_core (x, ctx->state, CHACHA_ROUNDS);
 
-      ctx->state[9] += (++ctx->state[8] == 0);
+      ctx->state[13] += (++ctx->state[12] == 0);
 
       /* stopping at 2^70 length per nonce is user's responsibility */