--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libtomcrypt/src/encauth/chachapoly/chacha20poly1305_decrypt.c	Fri Feb 09 23:49:22 2018 +0800
@@ -0,0 +1,49 @@
+/* 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"
+
+#ifdef LTC_CHACHA20POLY1305_MODE
+
+/**
+   Decrypt bytes of ciphertext with ChaCha20Poly1305
+   @param st      The ChaCha20Poly1305 state
+   @param in      The ciphertext
+   @param inlen   The length of the input (octets)
+   @param out     [out] The plaintext (length inlen)
+   @return CRYPT_OK if successful
+*/
+int chacha20poly1305_decrypt(chacha20poly1305_state *st, const unsigned char *in, unsigned long inlen, unsigned char *out)
+{
+   unsigned char padzero[16] = { 0 };
+   unsigned long padlen;
+   int err;
+
+   if (inlen == 0) return CRYPT_OK; /* nothing to do */
+   LTC_ARGCHK(st != NULL);
+
+   if (st->aadflg) {
+      padlen = 16 - (unsigned long)(st->aadlen % 16);
+      if (padlen < 16) {
+        if ((err = poly1305_process(&st->poly, padzero, padlen)) != CRYPT_OK) return err;
+      }
+      st->aadflg = 0; /* no more AAD */
+   }
+   if (st->aadflg) st->aadflg = 0; /* no more AAD */
+   if ((err = poly1305_process(&st->poly, in, inlen)) != CRYPT_OK)         return err;
+   if ((err = chacha_crypt(&st->chacha, in, inlen, out)) != CRYPT_OK)      return err;
+   st->ctlen += (ulong64)inlen;
+   return CRYPT_OK;
+}
+
+#endif
+
+/* ref:         $Format:%D$ */
+/* git commit:  $Format:%H$ */
+/* commit time: $Format:%ai$ */