krb5_kdc_rep_decrypt_proc
if ((retval = krb5_kdc_rep_decrypt_proc(context, key, &usage,
NULL, &as_key, krb5_kdc_rep_decrypt_proc,
NULL, &as_key, krb5_kdc_rep_decrypt_proc,
krb5_error_code krb5_kdc_rep_decrypt_proc