Included GCM in API documentation for Enc/Dec
diff --git a/doxygen/input/doc_encdec.h b/doxygen/input/doc_encdec.h
index a1b7e16..35cbc20 100644
--- a/doxygen/input/doc_encdec.h
+++ b/doxygen/input/doc_encdec.h
@@ -24,6 +24,7 @@
  *   - Camellia (see \c camellia_crypt_ecb(), \c camellia_crypt_cbc() and \c camellia_crypt_cfb128()).
  *   - DES/3DES (see \c des_crypt_ecb(), \c des_crypt_cbc(), \c des3_crypt_ecb() 
  *     and \c des3_crypt_cbc()).
+ *   - GCM (AES-GCM and CAMELLIA-GCM) (see \c gcm_init())
  *   - XTEA (see \c xtea_crypt_ecb()).
  * - Asymmetric:
  *   - Diffie-Hellman-Merkle (see \c dhm_read_public(), \c dhm_make_public()