Cryptography-Digest Digest #966, Volume #8 Tue, 26 Jan 99 10:13:05 EST
Contents:
Re: hardRandNumbGen (Mok-Kong Shen)
Re: The Performance of Meet-in-the-Middle (handWave)
Re: Random numbers from a sound card? (Mok-Kong Shen)
Re: Crack in Export Laws?? (Gurripato (x=nospam))
Re: Sanity check on authentication protocol ([EMAIL PROTECTED])
Cryptography FAQ (01/10: Overview) ([EMAIL PROTECTED])
Cryptography FAQ (02/10: Net Etiquette) ([EMAIL PROTECTED])
----------------------------------------------------------------------------
From: Mok-Kong Shen <[EMAIL PROTECTED]>
Subject: Re: hardRandNumbGen
Date: Tue, 26 Jan 1999 13:33:49 +0100
handWave wrote:
>
> > Even the presmption that the output would pass statistical tests is
> > questionable. One famous gafffe in PRNG design was Knuth's composite
> > generator, which he called superrandom. Unfortunately it was a closed loop
> > design.
>
> It was a computer program.
Having previously taken part in discussions in several threads of
this group on random number generations, I doubt nevertheless that
I have really known an answer to the following question:
If I have two sources of randomness, one software and one hardware,
both passing all statistical tests I apply equally well, why should
I choose one source in preference to the other? And if additionally
I don't know which sequence I get is from software and which is from
hardware? (Compare the Turing test.) How does the origin of the
sequence affect the workload of the analyst, if the software
generation process involves so many parameters that for combinatorical
reasons he has no chance of directly dealing with them but has
to try to look instead for possible regularities/irregularities in
the sequence itself and, by assumption, the sequences from the
two sources are of equal statistical quality? (Note that the
hardware source is (in my humble opinion) unpredictable simply
because there are so many participating 'parameters' that the
'summation' (the end product) becomes unpredictable, cf. the casting
of a dice.)
M. K. Shen
------------------------------
From: handWave <[EMAIL PROTECTED]>
Subject: Re: The Performance of Meet-in-the-Middle
Date: Tue, 26 Jan 1999 03:46:02 -1000
David Wagner wrote:
> By "almost" wrong, I mean that as far as I can tell the MITM attack has
> time complexity bounded by O(k * 2^k), which is only logarithmically slower
> (logarithmic in O(2^k)) than the naive estimate O(2^k).
> I could well be confused; it's easy for me to make mistakes when I try to
> do theory. If I am, I hope you'll point out where I went wrong.
O(2^k) = O(k * 2^k) by definition of Big Oh Notation
------------------------------
From: Mok-Kong Shen <[EMAIL PROTECTED]>
Subject: Re: Random numbers from a sound card?
Date: Tue, 26 Jan 1999 14:19:59 +0100
R. Knauer wrote:
> >I guess the issue of cryptological strength is inherently fuzzy
>
> Not really. The OTP system is proveably secure.
Once again I assert that this is a (for all practical purposes)
useless fact, because OTP presuppose (absolutely) true randomness
and there is no way of determining that in practice. I suppose
(with my meager knowledge of physics) this is almost the same as
saying at at at 0 Kelvin you can halt the motions of all atoms (but
you can't get to 0 Kelvin, only very close to it).
M. K. Shen
------------------------------
From: [EMAIL PROTECTED] (Gurripato (x=nospam))
Subject: Re: Crack in Export Laws??
Date: Tue, 26 Jan 1999 11:30:29 GMT
On Thu, 21 Jan 1999 18:19:43 -0500, "Kazak, Boris" <[EMAIL PROTECTED]>
wrote:
>Anybody having a comment on the following, which is posted
>at Netscape's site, please don't keep it secret!
>****************************************************
>Strong Encryption for International Banks
>
> STRONG ENCRYPTION
>The International Step-Up program allows international users of
>Communicator
>(previously restricted to 40-bit encryption) to "step up" to stronger
>encryption:
> 56-bit, 128-bit, or 168-bit.
Didnīt they hear about Fortify patch?
------------------------------
From: [EMAIL PROTECTED]
Subject: Re: Sanity check on authentication protocol
Date: Tue, 26 Jan 1999 13:11:54 GMT
In article <[EMAIL PROTECTED]>,
Antti Huima <[EMAIL PROTECTED]> wrote:
>
> > This protocol can be summarized as follows:
> >
> > A --> B: A, R_A
> > B --> A: {K, R_A, R_B}_S
> > A --> B: {R_B}_S
>
> If you want to do better you could send in the second message HASH(S |
> R_A) or something similar instead of R_A. Namely, you do not need to
> send R_A, it is enough that Alice is able to verify that Bob knows it.
> If you do it in some reasonable way like this, the known-plaintext
> problem diminishes.
But this does not protect against an attack on S. An attacker guessing S
can easily compute HASH(S | R_A) and so check his guess. The same seems
to be true for any other variation I can think of. It seems that what is
required is something that cannot be computed even after all plaintexts
are laid bare after being decrypted by S. This is why DH-EKE uses
Diffie-Hellman.
> The other problem with this protocol is that you need to change the
> shared secret often. Because the shared secret is used to encrypt
> messages with some redundancy (e.g. the known R_A in the original
> version), it is possible that the key used in the second and third
> messages gets eventually cracked. At this point the cracker can
> masquerade as the server as long as he wishes. To lessen this risk,
> change the effective shared secret periodically. Here is one
> suggestion to give an idea:
>
> Let S_1 be a shared secret.
>
> Add a nonce R_C that is sent in plain by B in the second message:
>
> B --> A: {K, R_A, R_B}_S, R_C
>
> User S = HASH(S_1|R_A|R_C) as the encryption key.
>
> In this way, the encryption key will be every time different. Still,
> only Bob and Alice can know it because it is derived from the "master"
> shared secret S_1.
I think you should be careful here. It's possible for an active adversary
to replace R_C by something else and so screw-up the update process, giving
A and B different ideas about what the shared secret is, and maybe making
it impossible for them to resynchronize - a dastardly DoS attack!. To
incorporate this idea I think the protocol needs to be made more explicit
in terms of verifying and accepting (by both A and B) the updated secret.
Paul(o)
============= Posted via Deja News, The Discussion Network ============
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------------------------------
From: [EMAIL PROTECTED]
Crossposted-To: talk.politics.crypto,sci.answers,news.answers,talk.answers
Subject: Cryptography FAQ (01/10: Overview)
Date: 26 Jan 1999 14:15:20 GMT
Reply-To: [EMAIL PROTECTED]
Archive-name: cryptography-faq/part01
Version: 1.0
Last-modified: 94/01/11
This is the first of ten parts of the sci.crypt FAQ. The parts are
mostly independent, but you should read this part before the rest. We
don't have the time to send out missing parts by mail, so don't ask.
Notes such as ``[KAH67]'' refer to the reference list in the last part.
Disclaimer: This document is the product of the Crypt Cabal, a secret
society which serves the National Secu---uh, no. Seriously, we're the
good guys, and we've done what we can to ensure the completeness and
accuracy of this document, but in a field of military and commercial
importance like cryptography you have to expect that some people and
organizations consider their interests more important than open
scientific discussion. Trust only what you can verify firsthand.
And don't sue us.
Many people have contributed to this FAQ. In alphabetical order:
Eric Bach, Steve Bellovin, Dan Bernstein, Nelson Bolyard, Carl Ellison,
Jim Gillogly, Mike Gleason, Doug Gwyn, Luke O'Connor, Tony Patti,
William Setzer. We apologize for any omissions.
If you have suggestions, comments, or criticism, please let the current
editors know by sending e-mail to [EMAIL PROTECTED] Bear in
mind that this is a work in progress; there are some questions which we
should add but haven't gotten around to yet. In making comments on
additions it is most helpful if you are as specific as possible and
ideally even provide the actual exact text.
Archives: sci.crypt has been archived since October 1991 on
ripem.msu.edu, though these archives are available only to U.S. and
Canadian users. Another site is rpub.cl.msu.edu in /pub/crypt/sci.crypt/
from Jan 1992. Please contact [EMAIL PROTECTED] if you know of
other archives.
The sections of this FAQ are available via anonymous FTP to rtfm.mit.edu
as /pub/usenet/news.answers/cryptography-faq/part[xx]. The Cryptography
FAQ is posted to the newsgroups sci.crypt, talk.politics.crypto,
sci.answers, and news.answers every 21 days.
The fields `Last-modified' and `Version' at the top of each part track
revisions.
Table of Contents
=================
1. Overview
2. Net Etiquette
2.1. What groups are around? What's a FAQ? Who am I? Why am I here?
2.2. Do political discussions belong in sci.crypt?
2.3. How do I present a new encryption scheme in sci.crypt?
3. Basic Cryptology
3.1. What is cryptology? Cryptography? Plaintext? Ciphertext? Encryption? Key?
3.2. What references can I start with to learn cryptology?
3.3. How does one go about cryptanalysis?
3.4. What is a brute-force search and what is its cryptographic relevance?
3.5. What are some properties satisfied by every strong cryptosystem?
3.6. If a cryptosystem is theoretically unbreakable, then is it
guaranteed analysis-proof in practice?
3.7. Why are many people still using cryptosystems that are
relatively easy to break?
3.8. What are the basic types of cryptanalytic `attacks'?
4. Mathematical Cryptology
4.1. In mathematical terms, what is a private-key cryptosystem?
4.2. What is an attack?
4.3. What's the advantage of formulating all this mathematically?
4.4. Why is the one-time pad secure?
4.5. What's a ciphertext-only attack?
4.6. What's a known-plaintext attack?
4.7. What's a chosen-plaintext attack?
4.8. In mathematical terms, what can you say about brute-force attacks?
4.9. What's a key-guessing attack? What's entropy?
5. Product Ciphers
5.1. What is a product cipher?
5.2. What makes a product cipher secure?
5.3. What are some group-theoretic properties of product ciphers?
5.4. What can be proven about the security of a product cipher?
5.5. How are block ciphers used to encrypt data longer than the block size?
5.6. Can symmetric block ciphers be used for message authentication?
5.7. What exactly is DES?
5.8. What is triple DES?
5.9. What is differential cryptanalysis?
5.10. How was NSA involved in the design of DES?
5.11. Is DES available in software?
5.12. Is DES available in hardware?
5.13. Can DES be used to protect classified information?
5.14. What are ECB, CBC, CFB, and OFB encryption?
6. Public-Key Cryptography
6.1. What is public-key cryptography?
6.2. How does public-key cryptography solve cryptography's Catch-22?
6.3. What is the role of the `trapdoor function' in public key schemes?
6.4. What is the role of the `session key' in public key schemes?
6.5. What's RSA?
6.6. Is RSA secure?
6.7. What's the difference between the RSA and Diffie-Hellman schemes?
6.8. What is `authentication' and the `key distribution problem'?
6.9. How fast can people factor numbers?
6.10. What about other public-key cryptosystems?
6.11. What is the `RSA Factoring Challenge?'
7. Digital Signatures
7.1. What is a one-way hash function?
7.2. What is the difference between public, private, secret, shared, etc.?
7.3. What are MD4 and MD5?
7.4. What is Snefru?
8. Technical Miscellany
8.1. How do I recover from lost passwords in WordPerfect?
8.2. How do I break a Vigenere (repeated-key) cipher?
8.3. How do I send encrypted mail under UNIX? [PGP, RIPEM, PEM, ...]
8.4. Is the UNIX crypt command secure?
8.5. How do I use compression with encryption?
8.6. Is there an unbreakable cipher?
8.7. What does ``random'' mean in cryptography?
8.8. What is the unicity point (a.k.a. unicity distance)?
8.9. What is key management and why is it important?
8.10. Can I use pseudo-random or chaotic numbers as a key stream?
8.11. What is the correct frequency list for English letters?
8.12. What is the Enigma?
8.13. How do I shuffle cards?
8.14. Can I foil S/W pirates by encrypting my CD-ROM?
8.15. Can you do automatic cryptanalysis of simple ciphers?
8.16. What is the coding system used by VCR+?
9. Other Miscellany
9.1. What is the National Security Agency (NSA)?
9.2. What are the US export regulations?
9.3. What is TEMPEST?
9.4. What are the Beale Ciphers, and are they a hoax?
9.5. What is the American Cryptogram Association, and how do I get in touch?
9.6. Is RSA patented?
9.7. What about the Voynich manuscript?
10. References
10.1. Books on history and classical methods
10.2. Books on modern methods
10.3. Survey articles
10.4. Reference articles
10.5. Journals, conference proceedings
10.6. Other
10.7. How may one obtain copies of FIPS and ANSI standards cited herein?
10.8. Electronic sources
10.9. RFCs (available from [FTPRF])
10.10. Related newsgroups
------------------------------
From: [EMAIL PROTECTED]
Crossposted-To: talk.politics.crypto,sci.answers,news.answers,talk.answers
Subject: Cryptography FAQ (02/10: Net Etiquette)
Date: 26 Jan 1999 14:15:27 GMT
Reply-To: [EMAIL PROTECTED]
Archive-name: cryptography-faq/part02
Last-modified: 94/06/13
This is the second of ten parts of the sci.crypt FAQ. The parts are
mostly independent, but you should read the first part before the rest.
We don't have the time to send out missing parts by mail, so don't ask.
Notes such as ``[KAH67]'' refer to the reference list in the last part.
The sections of this FAQ are available via anonymous FTP to rtfm.mit.edu
as /pub/usenet/news.answers/cryptography-faq/part[xx]. The Cryptography
FAQ is posted to the newsgroups sci.crypt, talk.politics.crypto,
sci.answers, and news.answers every 21 days.
Contents:
2.1. What groups are around? What's a FAQ? Who am I? Why am I here?
2.2. Do political discussions belong in sci.crypt?
2.3. How do I present a new encryption scheme in sci.crypt?
2.1. What groups are around? What's a FAQ? Who am I? Why am I here?
Read news.announce.newusers and news.answers for a few weeks. Always
make sure to read a newsgroup for some time before you post to it.
You'll be amazed how often the same question can be asked in the same
newsgroup. After a month you'll have a much better sense of what the
readers want to see.
2.2. Do political discussions belong in sci.crypt?
No. In fact some newsgroups (notably misc.legal.computing) were
created exactly so that political questions like ``Should RSA be
patented?'' don't get in the way of technical discussions. Many
sci.crypt readers also read misc.legal.computing, comp.org.eff.talk,
comp.patents, sci.math, comp.compression, talk.politics.crypto,
et al.; for the benefit of people who don't care about those other
topics, try to put your postings in the right group.
Questions about microfilm and smuggling and other non-cryptographic
``spy stuff'' don't belong in sci.crypt either.
2.3. How do I present a new encryption scheme in sci.crypt?
``I just came up with this neat method of encryption. Here's some
ciphertext: FHDSIJOYW^&%$*#@OGBUJHKFSYUIRE. Is it strong?'' Without a
doubt questions like this are the most annoying traffic on sci.crypt.
If you have come up with an encryption scheme, providing some
ciphertext from it is not adequate. Nobody has ever been impressed by
random gibberish. Any new algorithm should be secure even if the
opponent knows the full algorithm (including how any message key is
distributed) and only the private key is kept secret. There are some
systematic and unsystematic ways to take reasonably long ciphertexts
and decrypt them even without prior knowledge of the algorithm, but
this is a time-consuming and possibly fruitless exercise which most
sci.crypt readers won't bother with.
So what do you do if you have a new encryption scheme? First of all,
find out if it's really new. Look through this FAQ for references and
related methods. Familiarize yourself with the literature and the
introductory textbooks.
When you can appreciate how your cryptosystem fits into the world at
large, try to break it yourself! You shouldn't waste the time of tens
of thousands of readers asking a question which you could have easily
answered on your own.
If you really think your system is secure, and you want to get some
reassurance from experts, you might try posting full details of your
system, including working code and a solid theoretical explanation, to
sci.crypt. (Keep in mind that the export of cryptography is regulated
in some areas.)
If you're lucky an expert might take some interest in what you posted.
You can encourage this by offering cash rewards---for instance, noted
cryptographer Ralph Merkle is offering $1000 to anyone who can break
Snefru-4---but there are no guarantees. If you don't have enough
experience, then most likely any experts who look at your system will
be able to find a flaw. If this happens, it's your responsibility to
consider the flaw and learn from it, rather than just add one more
layer of complication and come back for another round.
A different way to get your cryptosystem reviewed is to have the NSA
look at it. A full discussion of this procedure is outside the scope
of this FAQ.
Among professionals, a common rule of thumb is that if you want to
design a cryptosystem, you have to have experience as a cryptanalyst.
------------------------------
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