"vedaal" <vedaal(_at_)hotmail(_dot_)com> writes:
Wouldn't that cause a CRC error, indicating that the message was tampered
with?
Or could a new CRC be calculated and included in the new re-encrypted
message?
Which CRC do you mean? Do you mean the armor CRC? That's re-created.
Internally, the signature and encryption are completely separable. If
you sign a message (note: NOT clearsigning), you would get the same
internal structure as you get when you sign and encrypt a message.
The only difference is that in the latter, when you encrypt, you take
the output from the signature transform and encrypt it, rather than
sending it to a file (or to ascii armor).
Also, could the MDC be utilized to prevent such substitutions, by detecting
alterations of any of the packets?
No, because the MDC could be recreated as well. The MDC is tied to K
but has no signature associated with it to tie it to the actual
sender.
Thanks,
vedaal
{i don't know, so am asking}
-derek
--
Derek Atkins
Computer and Internet Security Consultant
derek(_at_)ihtfp(_dot_)com www.ihtfp.com