Corrupting files

[utternoncesense at gmail.com]

If your modus operandi includes exchanging secret information outside
of normal channels (e.g., "change the case of the nth letter") you
would be better off exchanging more secure information than a single
change like that.  For example - a second set of public keys.  Encyrpt
your document twice, first with your friend's "private" public key,
then with his public-public key.  Or exchange the passphrase to a
symetrically encrypted file, then encypt the symmetrically encrypted
file with his public key.

Hell, try one-time pads.