--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/encauth/gcm/gcm_done.c	Fri May 06 13:23:02 2005 +0000
@@ -0,0 +1,77 @@
+/* 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.
+ *
+ * Tom St Denis, [email protected], http://libtomcrypt.org
+ */
+
+/**
+   @file gcm_done.c
+   GCM implementation, Terminate the stream, by Tom St Denis
+*/
+#include "tomcrypt.h"
+
+#ifdef GCM_MODE
+
+/**
+  Terminate a GCM stream
+  @param gcm     The GCM state
+  @param tag     [out] The destination for the MAC tag
+  @param taglen  [in/out]  The length of the MAC tag
+  @return CRYPT_OK on success
+ */
+int gcm_done(gcm_state *gcm, 
+                     unsigned char *tag,    unsigned long *taglen)
+{
+   unsigned long x;
+   int err;
+
+   LTC_ARGCHK(gcm     != NULL);
+   LTC_ARGCHK(tag     != NULL);
+   LTC_ARGCHK(taglen  != NULL);
+
+   if (gcm->buflen > 16 || gcm->buflen < 0) {
+      return CRYPT_INVALID_ARG;
+   }
+
+   if ((err = cipher_is_valid(gcm->cipher)) != CRYPT_OK) {
+      return err;
+   }
+
+
+   if (gcm->mode != GCM_MODE_TEXT) {
+      return CRYPT_INVALID_ARG;
+   }
+
+   /* handle remaining ciphertext */
+   if (gcm->buflen) {
+      gcm->pttotlen += gcm->buflen * CONST64(8);
+      gcm_mult_h(gcm, gcm->X);
+   }
+
+   /* length */
+   STORE64H(gcm->totlen, gcm->buf);
+   STORE64H(gcm->pttotlen, gcm->buf+8);
+   for (x = 0; x < 16; x++) {
+       gcm->X[x] ^= gcm->buf[x];
+   }
+   gcm_mult_h(gcm, gcm->X);
+
+   /* encrypt original counter */
+   cipher_descriptor[gcm->cipher].ecb_encrypt(gcm->Y_0, gcm->buf, &gcm->K);
+   for (x = 0; x < 16 && x < *taglen; x++) {
+       tag[x] = gcm->buf[x] ^ gcm->X[x];
+   }
+   *taglen = x;
+
+   cipher_descriptor[gcm->cipher].done(&gcm->K);
+
+   return CRYPT_OK;
+}
+
+#endif
+