void sha2_hmac_starts( sha2_context *ctx, const unsigned char *key, size_t keylen, int is224 );
void sha2_hmac_update( sha2_context *ctx, const unsigned char *input, size_t ilen );
void sha2_hmac_finish( sha2_context *ctx, unsigned char output[32] );
void sha2_hmac_starts( sha2_context *ctx, const unsigned char *key, size_t keylen, int is224 );
void sha2_hmac_update( sha2_context *ctx, const unsigned char *input, size_t ilen );
void sha2_hmac_finish( sha2_context *ctx, unsigned char output[32] );