A.19. KRB_CRED verification

        receive packet;
        if (packet.pvno != 5) then
                either process using other protocol spec
                or error_out(KRB_AP_ERR_BADVERSION);
        endif
        if (packet.msg-type != KRB_CRED) then
                error_out(KRB_AP_ERR_MSG_TYPE);
        endif

        cleartext := decrypt(packet.enc-part) using negotiated key;
        if (decryption_error()) then
                error_out(KRB_AP_ERR_BAD_INTEGRITY);
        endif
        if ((packet.r-address is present or required) and
           (packet.s-address != O/S_sender(packet)) then
            /* O/S report of sender not who claims to have sent it */
            error_out(KRB_AP_ERR_BADADDR);
        endif
        if ((packet.r-address is present) and
            (packet.r-address != local_host_address)) then
                /* was not sent to proper place */
                error_out(KRB_AP_ERR_BADADDR);
        endif
        if (not in_clock_skew(packet.timestamp,packet.usec)) then
                error_out(KRB_AP_ERR_SKEW);
        endif
        if (repeated(packet.timestamp,packet.usec,packet.s-address))
                then error_out(KRB_AP_ERR_REPEAT);
        endif
        if (packet.nonce is required or present) and
           (packet.nonce != expected-nonce) then
                error_out(KRB_AP_ERR_MODIFIED);
        endif

        for (ticket[n] in tickets that were forwarded) do
                save_for_later(ticket[n],key[n],principal[n],
                               server[n],times[n],flags[n]);
        return