krb5_k_decrypt_iov
krb5_k_decrypt_iov( context, key, 7, 0, iov, 2));
krb5_k_decrypt_iov(context, key, 7, 0, iov, 5));
ret = krb5_k_decrypt_iov(context, key, usage, cipher_state, data,
code = krb5_k_decrypt_iov(context, key, usage, state, kiov, kiov_len);