krb5_c_decrypt_iov
krb5_c_decrypt_iov( context, keyblock, 7, 0, iov, 2));
krb5_c_decrypt_iov(context, keyblock, 7, 0, iov, 5));
ret = krb5_c_decrypt_iov(NULL, &keyblock, 0, NULL, iov, 2);