encryption bloats file

[Robert J. Hansen]

Scott Lambdin wrote:
> Someone sends us a big ~700MB pgp encrypted file and when we decrypt it
> the resulting file is about half that size.  Anyone have an idea what
> they might be doing to swell it up like that?

Option 1: they're not using compression and they're ASCII-armoring the
file.  You can expect to see a large size swell.

Option 2: they're sending a file that's carefully crafted to blow up.
I've seen a ridiculously tiny zip archive (a couple of K) that expands
into hundreds of terabytes.  There are sixteen zip archives in that zip
archive, each zip archive expands into another sixteen zip archives,
each of those zip archives expands into several gigs of zeros, etc., etc.