MDC/Non-MDC mode question

[Kahil D. Jallad]

Hello,
	I'm doing some research with gpg and I was hoping someone could
help me with this question:
GPG's default behavior is to use a message digest at the end of an
encrypted message. (The Symettrically Encrypted Data Packet is followed by
20 bytes of hash) At first glance it seems simple to change the
MDC packet to a "normal" OpenPGP Encrypted Message packet since the packet
headers are in the clear, but this is not the case (by design I am sure).
>From experiments, it seems that MDC protected packets and non-mdc packets
use a slightly different mode of encryption, but I can't find this in the
code,  i.e. as far as I can tell non-mdc packets and mdc packets do the
same things with  as cipher resyncs and CFB encryption . . .

If someone could point me towards the file in the source where this
happens, or give me any information concerning the difference in
formats/processing of mdc vs. non-mdc packets in gpg, I would be greatly
appreciative...

Thanks,
Kahil Jallad