On Thu, 3 Mar 1994 wcs@anchor.ho.att.com wrote:
The problem is the length field - you've got to have it, and it's recognizeable because it begins with a run of 0s. [several hiding approaches.] Actually, you don't really need it, at least for PGP. PGP messages keep
Jef Poskanzer writes: track of how much real stuff the message has, and ought to be able to do the right thing if there's extra stuff at the end; I'd guess that Stealth-PGP can do the same. I realize PGP isn't the only thing people will want to hide, but most things need hiding have enough structure to them thatpadding wiht garbage at the end is no problem.
On the other hand, if you do have a length field, you do have to do something reasonable with it, and just putting it at the beginning makes it difficult to do other stuff with the stego program, like inserting text bitplanes into a picture....
Bill
Sorry to have to bring this up, but... As some of the newbies have pointed out, in previous messages on this thread: The length field, or any standard-length header scattered (standardly :) through the beginning of the file will cost one no loss in security if it is encrypted. The encryption could easily be standardized via a public-key based algorithm like PGP. The stego-program could be kept simple by meerly having it call PGP to do the header-encryption work. Sergey