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14. Other Advanced Crypto Applications
14.1. copyright
THE CYPHERNOMICON: Cypherpunks FAQ and More, Version 0.666,
1994-09-10, Copyright Timothy C. May. All rights reserved.
See the detailed disclaimer. Use short sections under "fair
use" provisions, with appropriate credit, but don't put your
name on my words.
14.2. SUMMARY: Other Advanced Crypto Applications
14.2.1. Main Points
14.2.2. Connections to Other Sections
14.2.3. Where to Find Additional Information
- see the various "Crypto" Proceedings for various papers on
topics that may come to be important
14.2.4. Miscellaneous Comments
14.3. Digital Timestamping
14.3.1. digital timestamping
- The canonical reference for digital timestamping is the
work of Stu Haber and Scott Stornetta, of Bellcore. Papers
presented at various Crypto conferences. Their work
involves having the user compute a hash of the document he
wishes to be stamped and sending the hash to them, where
they merge this hash with other hashes (and all previous
hashes, via a tree system) and then they *publish* the
resultant hash in a very public and hard-to-alter forum,
such as in an ad in the Sunday "New York Times."
In their parlance, such an ad is a "widely witnessed
event," and attempts to alter all or even many copies of
the newspaper would be very difficult and expensive. (In a
sense, this WWE is similar to the "beacon" term Eric Hughes
used.)
Haber and Stornetta plan some sort of commercial operation
to do this.
This service has not yet been tested in court, so far as I
know. The MIT server is an experiment, and is probably
useful for experimenting. But it is undoubtedly even less
legally significant, of course.
14.3.2. my summary
14.4. Voting
14.4.1. fraud, is-a-person, forging identies, increased "number"
trends
14.4.2. costs also high
14.4.3. Chaum
14.4.4. voting isomorphic to digital money
- where account transfers are the thing being voted on, and
the "eligible voters" are oneself...unless this sort of
thing is outlawed, which would create other problems, then
this makes a form of anonymous transfer possible (more or
less)
14.5. Timed-Release Crypto
14.5.1. "Can anything like a "cryptographic time capsule" be built?"
- This would be useful for sealing diaries and records in
such a way that no legal bodies could gain access, that
even the creator/encryptor would be unable to decrypt the
records. Call it "time escrow." Ironically, a much more
correct use of the term "escrow" than we saw with the
government's various "key escrow" schemes.
- Making records undecryptable is easy: just use a one-way
function and the records are unreachable forever. The trick
is to have a way to get them back at some future time.
+ Approaches:
+ Legal Repository. A lawyer or set of lawyers has the key
or keys and is instructed to release them at some future
time. (The key-holding agents need not be lawyers, of
course, though that is the way things are now done.
- The legal system is a time-honored way of protecting
secrets of various kinds, and any system based on
cryptography needs to compete strongly with this simple
to use, well-established system.
- If the lawyer's identity is known, he can be
subpoenaed. Depends on jurisdictional issues, future
political climate, etc.
- But identity-hiding protocols can be used, so that the
lawyer cannot be reached. All that is know, for
example, is that "somewhere out there" is an agent who
is holding the key(s). Reputation-based systems should
work well here: the agent gains little and loses a lot
by releasing a key early, hence has no economic
motivation to do so. (Picture also a lot of "pinging"
going to "rate" the various ti<w agents.)
- Cryptography with Beacons. A "beacon agent" makes very
public a series of messages, somehow. Details fuzzy. [I
have a hunch that using digital time-stamping services
could be useful here.]
+ Difficulty of factoring, etc.
+ The idea here is to-use a function which is presently
hard to invert, but which may be easier in the future.
This is fraught with problems, including
unpredictability of the difficulty, imprecision in the
timing of release, and general clumsiness. As Hal
Finney notes:
- "There was an talk on this topic at either the Crypto
92 or 93 conference, I forget which. It is available
in the proceedings....The method used was similar to
the idea here of encrypting with a public key and
requiring factoring of the modulus to decrypt. But
the author had more techniques he used, iterating
functions forward which would take longer to iterate
backwards. The purpose was to give a more
predictable time to decrypt.....One problem with this
is that it does not so much put a time floor on the
decryption, but rather a cost floor. Someone who is
willing to spend enough can decrypt faster than
someone who spends less. Another problem is the
difficulty of forecasting the growth of computational
power per dollar in the future." [Hal Finney,
sci.crypt, 1994-8-04]
+ Tamper-resistant modules. A la the scheme to send the
secrets to a satellite in orbit and expect that it will
be prohibitively expensive to rendezvous and enter this
satellite.
- Or to gain access to tamper-resistant modules located
in bank vaults, etc.
- But court orders and black bag jobs still are factors.
14.5.2. Needs
- journalism
+ time-stamping is a kind of example
- though better seen in the conventional analysis
- persistent institutions
- shell games for moving money around, untraceably
14.5.3. How
- beacons
- multi-part keys
- contracted-for services (like publishing keys)
- Wayner, my proposal, Eric Hughes
14.6. Traffic Analysis
14.6.1. digital form, and headers, LEAF fields, etc., make it vastly
easier to know who has called whom, for how long, etc.
14.6.2. (esp. in contrast to purely analog systems)
14.7. Steganography
14.7.1. (Another one of the topics that gets a lot of posts)
14.7.2. Hiding messages in other messages
- "Kevin Brown makes some interesting points about
steganography and steganalysis. The issue of recognizing
whether a message has or mighthave a hidden message has two
sides. One is for the desired recipient to be clued that
he should try desteganizing and decrypting the message, and
the other is for a possible attacker to discover illegal
uses of cryptography.
"Steganography should be used with a "stealthy"
cryptosystem (secret key or public key), one in which the
cyphertext is indistinguishable from a random bit string.
You would not want it to have any headers which could be
used to confirm that a desteganized message was other than
random noise." [Hal Finney, 1993-05-25]
14.7.3. Peter Wayner's "Mimic"
- "They encode a secret message inside a harmless looking
ASCII text file. This is one of the very few times
the UNIX tools "lex" and "yacc" have been used in
cryptography, as far as I know. Peter Wayner, "Mimic
Functions", CRYPTOLOGIA Volume 16, Number 3, pp. 193-214,
July 1992.[Michael Johnson, sci.crypt, 1994-09-05]
14.7.4. I described it in 1988 or 89 and many times since
- Several years ago I posted to sci.crypt my "novel" idea for
packing bits into the essentially inaudible "least
significant bits" (LSBs) of digital recordings, such as
DATs and CDs. Ditto for the LSBs in an 8-bit image or 24-
bit color image. I've since seen this idea reinvented
_several_ times on sci.crypt and elsewhere...and I'm
willing to bet I wasn't the first, either (so I don't claim
any credit).
A 2-hour DAT contains about 10 Gbits (2 hours x 3600 sec/hr
x 2 channels x 16 bits/sample x 44K samples/sec), or about
1.2 Gbytes. A CD contains about half this, i.e., about 700
Mbytes. The LSB of a DAT is 1/16th of the 1.2 Gbytes, or 80
Mbytes. This is a _lot_ of storage!
A home-recorded DAT--and I use a Sony D-3 DAT Walkman to
make tapes--has so much noise down at the LSB level--noise
from the A/D and D/A converters, noise from the microphones
(if any), etc.--that the bits are essentially random at
this level. (This is a subtle, but important, point: a
factory recorded DAT or CD will have predetermined bits at
all levels, i.e., the authorities could in principle spot
any modifications. But home-recorded, or dubbed, DATs will
of course not be subject to this kind of analysis.) Some
care might be taken to ensure that the statistical
properties of the signal bits resemble what would be
expected with "noise" bits, but this will be a minor
hurdle.
Adobe Photoshop can be used to easily place message bits in
the "noise" that dominates things down at the LSB level.
The resulting GIF can then be posted to UseNet or e-mailed.
Ditto for sound samples, using the ideas I just described
(but typically requiring sound sampling boards, etc.). I've
done some experiments along these lines.
This doesn't mean our problems are solved, of course.
Exchanging tapes is cumbersome and vulnerable to stings.
But it does help to point out the utter futility of trying
to stop the flow of bits.
14.7.5. Stego, other versions
- Romana Machado's Macintosh stego program is located in the
compression files, /cmp, in the sumex-aim@stanford.edu info-
mac archives.
- "Stego is a tool that enables you to embed data in, and
retrieve data from, Macintosh PICT format files, without
changing the appearance of the PICT file. Though its
effect is visually undetectable, do not expect
cryptographic security from Stego. Be aware that anyone
with a copy of Stego can retrieve your data from your PICT
file. Stego can be used as an "envelope" to hide a
_previously encrypted_ data file in a PICT file, making it
much less likely to be detected." [Romana Machado, 1993-11-
23]
14.7.6. WNSTORM, Arsen Ray Arachelian
14.7.7. talk about it being used to "watermark" images
14.7.8. Crypto and steganography used to plant false and misleading
nuclear information
- "Under a sub-sub-sub-contract I once worked on some phony
CAD drawings for the nuclear weapons production process,
plotting false info that still appears in popular books,
some of which has been posted here....The docs were then
encrypted and stegonagraphied for authenticity. We were
told that they were turned loose on the market for this
product in other countries." [John Young, 1994-08-25]
- Well...
14.7.9. Postscript steganography
- where info is embedded in spacings, font characteristics
(angles, arcs)
- ftp://research.att.com/dist/brassil/infocom94.ps
- the essential point: just another haystack to hide a needle
14.8. Hiding cyphertext
14.8.1. "Ciphertext can be "uncompressed" to impose desired
statistical properties. A non-adaptive first-order
arithmetic decompression will generate first-order symbol
frequencies that emulate, for instance, English text." [Rick
F. Hoselton, sci.crypt, 1994-07-05]
14.9. 'What are tamper-responding or tamper-resistant modules?"
14.9.1. The more modern name for what used to be called "tamper-proof
boxes"
14.9.2. Uses:
- alarmed display cases, pressure-sensitive, etc. (jewels,
art, etc.)
+ chips with extra layers, fuses, abrasive comounds in the
packaging
- to slow down grinding, etching, other depotting or
decapping methods
- VLSI Technology Inc. reportedly uses these methods in its
implementation of the MYK-78 "Clipper" (EES) chip
- nuclear weapons ("Permissive Action Links," a la Sandia,
Simmons)
- smartcards that give evidence of tampering, or that become
inactive
+ as an example, disk drives that erase data when plug is
pulled, unless proper code is first entered
- whew! pretty risky (power failures and all), but needed
by some
- like "digital flash paper"
14.9.3. Bypassing tamper-responding or tamper-resistant technologies
- first, you have to _know_
14.10. Whistleblowing
14.10.1. This was an early proposed use (my comments on it go back to
1988 at least), and resulted in the creation of
alt.whisteblowers.
- So far, nothing too earth-shattering
14.10.2. outing the secret agents of a country, by posting them
anonymously to a world-wide Net distribution....that ought to
shake things up
14.11. Digital Confessionals
14.11.1. religious confessionals and consultations mediated by digital
links...very hard for U.S. government to gain access
14.11.2. ditto for attorney-client conversations, for sessions with
psychiatrists and doctors, etc.
14.11.3. (this does not meen these meetings are exempt from the
law...witness Feds going after tainted legal fees, and
bugging offices of attorneys suspected of being in the drug
business)
14.12. Loose Ends
14.12.1. Feigenbaum's "Computing with Encrypted Instances"
work...links to Eric Hughes's "encrypted open books" ideas.
- more work needed, clearly