--- /dev/null
+/* 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.
+ */
+
+/**
+ @file gcm_done.c
+ GCM implementation, Terminate the stream, by Tom St Denis
+*/
+#include "tomcrypt.h"
+
+#ifdef LTC_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 == LTC_GCM_MODE_IV) {
+ /* let's process the IV */
+ if ((err = gcm_add_aad(gcm, NULL, 0)) != CRYPT_OK) return err;
+ }
+
+ if (gcm->mode == LTC_GCM_MODE_AAD) {
+ /* let's process the AAD */
+ if ((err = gcm_process(gcm, NULL, 0, NULL, 0)) != CRYPT_OK) return err;
+ }
+
+ if (gcm->mode != LTC_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 */
+ if ((err = cipher_descriptor[gcm->cipher].ecb_encrypt(gcm->Y_0, gcm->buf, &gcm->K)) != CRYPT_OK) {
+ return err;
+ }
+ 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
+
+
+/* ref: $Format:%D$ */
+/* git commit: $Format:%H$ */
+/* commit time: $Format:%ai$ */