-----BEGIN PGP SIGNED MESSAGE----- There has been some discussion on steganography in the past few days. I've been thinking about the subject so here is a list of my random thoughts: 1. Steganography "standard": Current steganography software relies almost totally on security through obscurity. The problem with such an approach is that there is no standard way to extract data from .gif or .jpg files. If two people want to communicate using stego, they have to have some secure channel through which they could negotiate a protocol that could extract information from data files. This brings up the same Catch-22 situation that exists with conventional cryptography. My idea is that there should be some common, well-known way to de-stego data files. This really doesn't weaken the security of any stego software because if strong crypto that doesn't append any headers on to the message is used in conjunction with stego software, then the output of a stego program would just appear to be random garbage. There would be no way for the feds to prove that the random data was encrypted. I don't know much about graphic and sound file formats, but I think that in most cases the least-significant bit of a graphics or sound file should be pretty random anyway. 2. Recognizing stegoed data: Another problem with stegonography is that while many programs use some kind of identifying header so the recipient can tell whether the file contains hidden information or not, this also allows a snooper to determine the same thing. I think that the ability for the recipient to identify whether the data is stegoed or not is important. So I came up with the idea of using a MAC keyed with the session key used to encrypt the hidden data for checking if the picture contains stegoed data. With this approach, an attacker would not be able to verify if a file contained hidden data or not since the session key would be encrypted with the recipient's public key. 3. Message pools: With steganography more widespread, the use of message pools becomes a lot more interesting. People could communicate anonymously using one of the alt.binaries.* groups with everyone else reading the group completely oblivious to this fact. The posts would be pictures that would decode normally, but only the recipient would be able to decrypt the hidden data. Since the binaries newsgroups are among the most popular on the Usenet, reading one of the binaries newsgroups would draw less suspicion then reading alt.anonymous.messages. I don't know how reliable some of the binaries groups are since many NNTP servers don't carry them or expire the articles early, but since cross-posting seems to be fairly common on those newsgroups anyway, a cross-posted file with stegoed data would have a good chance of reaching the recipient. - -- Mark PGP encrypted mail prefered Key fingerprint = d61734f2800486ae6f79bfeb70f95348 http://www.voicenet.com/~markm/ -----BEGIN PGP SIGNATURE----- Version: 2.6.3 Charset: noconv iQCVAwUBMe6OdLZc+sv5siulAQHMOAP/Yv6SLWY/CCXzXj/91q0hh2M3oVjMr7a6 RBEKCaExosbjJojoTlM9epyzO/gC4jrAj+3IIeciPLHyJPgF2CJmW3NU4bRHPls5 d2kEUPCIc/mLVcbieEC4OO7QlYeFY0vIBn+y1CO3V0kLN20N6Y3845p4a7BY6Wa+ u7dE12QbZLc= =8xQ7 -----END PGP SIGNATURE-----