The meaning must still be in clear but you are allowed to send a authenticating "signature" in code, as long as the signature contains no information other than authentication itself that was not also transmitted in clear. That's why autopatch

Hmm... if authenticating signatures can be transmitted, then some enterprising and patient cryptographers can also transmit messages, encrypted if desired, back and forth using one of the "subliminal channel" protocols! A subliminal channel allows people to communicate by essentially disguising their true message in the digital signature of the message they transmit openly. It would take several exchanges between the two to transmit a real message, since I recall the subliminal channels I've looked at allow the transfer of a few numbers at a time, but it could be done! /-----------------------------------\ | Karl L. Barrus | | elee9sf@menudo.uh.edu | <- preferred address | barrus@tree.egr.uh.edu (NeXTMail) | \-----------------------------------/