+ const void *in, size_t inlen, char *resbuf);
+extern Gc_rc gc_hmac_sha256 (const void *key, size_t keylen,
+ const void *in, size_t inlen, char *resbuf);
+extern Gc_rc gc_hmac_sha512 (const void *key, size_t keylen,
+ const void *in, size_t inlen, char *resbuf);