ISC_SHA1_BLOCK_LENGTH
if (r.length > ISC_SHA1_BLOCK_LENGTH) {
unsigned char key[ISC_SHA1_BLOCK_LENGTH];
isc_hmacsha1_init(hmacsha1ctx, hkey->key, ISC_SHA1_BLOCK_LENGTH);
#define ISC_HMACSHA1_KEYLENGTH ISC_SHA1_BLOCK_LENGTH