STEG: a real-life use for steganography
I had an extremely interesting conversation with a fellow last night, say, X. A mutual friend of ours had steered him towards me. X has contacts in a country C which will remain nameless. The government of C is extremely repressive and has a large internal police force. The situation, evidently, is one similar to the old USSR, where masks behind masks were used in daily life, little is exactly as it appears, and the default discourse is sideways speaking. The scenario is almost worst-case. There is a need for steganography, since the use of cryptography is grounds for suppression; likewise there is a need for covert channels. There is a need for double-blinding of identities, since one's friends may be difficult to detect. And so on. The aspect that _is_ good is that C is not the whole world, and there are plenty of us not in C. The first most useful facility to set up, X thinks, is simply news from outside of C as a bypass of the media in C--wire service articles about C, for example, as well as a feed of the newsgroup "soc.culture.<C>". Here's the technique we came up with last night. C has an indigenous music M which is periodically performed in the United States. We were thinking about pressing short-run CD's of these live performances. We all know where the news feeds go. The CD's would be distributed via standard music channels and would be surprisingly brisk sellers. The costs of the project can evidently be footed by willing members of the M industry in C. Now let me address the standard comment "Oh, steganography completely solves that problem." Please. That's like saying, "Oh, just use an internal combustion engine to solve your long distance transport problems." Such statements are a failure of imagination and seriousness. A practical system to carry this project out is quite large. I see at least the following pieces needed: -- A facility to gather the data being put on the disks. This by itself is no trivial task, since it involves the collection of many disparate sources. -- An authoring system to arrange the data, once collected, into a usable structure. -- An encryption system for the arranged data. Such a system can't treat the data as one long stream, because of the segmented nature of the data. The ability to mount the CD as a file system would be good leverage for other programmers. -- A mastering system to combine a music master CD (done separately) and a data master (in some format) into a new music master CD. This will, at the least require a machine with a CD reader and writer. Blank media, FYI, for a CD writer are about $20/disk. The CD writer is about $5K. These numbers are approximate and falling rapidly. -- A CD pressing facility. These are commercially available at quite reasonable cost in quantities in the 100's. -- A CD distribution system. This will likely be the M industry, and thankfully the details of international shipping and customs will be taken care of, as well as retail distribution. -- A decryption system to get the data off the CD. -- Client software to make use of the information. It need not all be in text format. -- A key distribution system. A secret key per CD and word of mouth may be sufficient. A system to make rememberable sentences out of an arbitrary 128 bits (and the inverse) would be useful to facilitate word of mouth. This is no small task. Those interested in participating may start working on any of the above. The tasks are fairly separable. Here are some that I can identify as critical. -- A standard for encoding data into the low bits of an audio CD. This will likely require a lot of specific knowledge of the low level encoding and error correction systems used in CD's. I do know that they are not simple, being much more than bit-correcting linear codes. -- A standard for the encoding of file system data onto these low bits. This should be a separate document, even though the design of this will be influenced by the bit encoding standard. Some adaptation of existing file system standards may be appropriate. -- A standard for the encryption format for the file system. It may be that Matt Blaze's CFS cryptograpy can be lifted wholesale. -- Multiplatform software support for all of the above. I am pleased to have a real example to work on, rather than a lot of wixering about hypotheticals. I welcome discussion of this topic. Eric
I think the proposed scheme is a little top-heavy. What's wrong with clear text? When the Shah still governed Iran, the followers of Khomeini would smuggle his speeches into the country (in clear-text) on cassette tapes of Western popular music. I guess you could call this steganography --- so many ``legitimate'' copies of the tapes were pouring into the country, that the ``subversive'' ones were hard to find among them. I think the tapes actually held a few minutes' worth of the original music, to discourage those zealous customs agents who would actually listen to part of the tape to make sure it is authentic. Similar things existed in the Soviet Union, where they were known as ``Magnetizdat''. And, well, if the police have already gone to the length of confiscating your tapes and listening to them all to find the ones which contain Khomeini's speeches, they've also probably already got you on the train for the Gulag, no matter what they find.
The biggest problem I see with your scheme is that it won't remain secret for very long, and the government will probably just ban all CD imports as a result. And possession of a CD player or CDs (even "legit" ones) would be enough to send you off to kamp.
-- A decryption system to get the data off the CD.
There's a practical problem here. Audio CD players generally provide no easy way to get the raw bits into a computer (SPDIF interface cards exist for PCs, but they're rare and expensive). And I haven't yet figured out how to get a CD-ROM drive to read the raw bits off an audio CD; I suspect it requires munging the firmware in the drive, which makes anything you do highly manufacturer specific. Phil
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There's a practical problem here. Audio CD players generally provide no easy way to get the raw bits into a computer (SPDIF interface cards exist for PCs, but they're rare and expensive). And I haven't yet figured out how to get a CD-ROM drive to read the raw bits off an audio CD; I suspect it requires munging the firmware in the drive, which makes anything you do highly manufacturer specific.
Apple's CD-300/300i drives can read audio bits directly and turn them into a QuickTime sound channel, as can SGI's SCSI CD. Apple uses a Sony mechanism, and SGI uses a Toshiba. The SGI drives use modified firmware and (AFAIK) are not available elsewhere, but you can get the Apple drives at Circuit City, Sears, etc. With the right sequence of SCSI commands you could easily capture an "audio" bitstream, then munge it as desired to extract the stegged data, play it backwards, or whatever. IIR, code to directly read arbitrary audio data on an Apple CD-ROM was recently posted in comp.sys.mac.programmer, but I didn't save it. - -Paul - -- Paul Robichaux, KD4JZG | "Though we live in trying times perobich@ingr.com | We're the ones who have to try." - Neil Peart Intergraph Federal Systems | Be a cryptography user- ask me how. Of course I don't speak for Intergraph. -----BEGIN PGP SIGNATURE----- Version: 2.3a iQCVAgUBLVen7SA78To+806NAQG3sAQAu8prXRUkJKWwmQBIeJxwQIDK+2ilvyxe 24rcK89EInIyEdLnsSrx4uly3CBpS7iWdOmoAQ9tNu5tOOi3xc+5W5cvUTJ4t/NR gblnKM/qevO6PCdQFiJXNgzg/1DkY2LsrvnH3I+8lxXeNn06CQKB85r5COY2vL3I ldqrGjLScHU= =GjEo -----END PGP SIGNATURE-----
Hunh. I'm surprised that you would select a fixed medium (CDs) for a variable information source. How often do you plan to press new CDs? Would it not be simpler to use steganography to encode the desired information into GIFs of, say, US weather maps? These maps are revised quite often and it would be natural to send person X a new weather map every day or so. Yes, as we all know from past discussions, it's possible for someone who knows what you're doing to recover the data "hidden" in the pictures. But how likely is that to happen? What's the cost of this (or another non- media-dependent solution) versus the complexity and cost of using CDs as your transport mechanism? [About the CDs: what will the sound like when played on a normal CD player? Isn't this likely to attract attention?] --Alan Wexelblat, Reality Hacker, Author, and Cyberspace Bard Media Lab - Advanced Human Interface Group wex@media.mit.edu Voice: 617-258-9168 Page: 617-945-1842 an53607@anon.penet.fi All the world's a stage and most of us are desperately unrehearsed.
participants (5)
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Alan (Miburi-san) Wexelblat -
dm@hri.com -
hughes@ah.com -
paul@poboy.b17c.ingr.com -
Phil Karn