Cryptography-Digest Digest #778, Volume #11 Mon, 15 May 00 15:13:01 EDT
Contents:
Re: Notes on the "Vortex" block cipher (Terry Ritter)
Re: Notes on the "Vortex" block cipher (Terry Ritter)
Re: (May 11, 2000) Cipher Contest Update (Mike Rosing)
Re: Definition of "Broken" Cipher (Mok-Kong Shen)
Cryptography FAQ (01/10: Overview) ([EMAIL PROTECTED])
Cryptography FAQ (02/10: Net Etiquette) ([EMAIL PROTECTED])
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From: [EMAIL PROTECTED] (Terry Ritter)
Subject: Re: Notes on the "Vortex" block cipher
Date: Mon, 15 May 2000 17:18:20 GMT
On Mon, 15 May 2000 13:39:08 +0200, in
<[EMAIL PROTECTED]>, in sci.crypt Runu Knips
<[EMAIL PROTECTED]> wrote:
>Tom St Denis wrote:
>> There is some science behind cryptography whether you want to believe
>> it or not.
>
>And I think his dislike of Blowfish is only instinctive. I would trust
>Blowfish, too. It only requires a little bit too much resources for
>some applications.
That particular answer of mine would have been the same for any other
cipher. The problem is not a particular cipher, the problem is in
trusting something which cannot be tested to see how closely it comes
to doing what we want it to do.
---
Terry Ritter [EMAIL PROTECTED] http://www.io.com/~ritter/
Crypto Glossary http://www.io.com/~ritter/GLOSSARY.HTM
------------------------------
From: [EMAIL PROTECTED] (Terry Ritter)
Subject: Re: Notes on the "Vortex" block cipher
Date: Mon, 15 May 2000 17:18:31 GMT
On Mon, 15 May 2000 09:49:22 GMT, in <8foh6v$mib$[EMAIL PROTECTED]>, in
sci.crypt Tom St Denis <[EMAIL PROTECTED]> wrote:
>In article <[EMAIL PROTECTED]>,
> [EMAIL PROTECTED] (Terry Ritter) wrote:
>> Nonsense. That is *not* the same at all:
>>
>> In all normal fields of engineering design (and I am a professional
>> engineer), engineers can test their work. Most designs will have
>> specifications, and the resulting equipment can be tested to see if it
>> meets those specifications. In most areas of life, we can detect
>> design bugs simply because the machine (including software) does not
>> do what we want it to: it does not meet specs.
>
>Hindenburg. Nuff said.
Nonsense. When the Hindenberg went down *everybody* *knew* that a
disaster had happened. CRYPTOGRAPHY IS NOT LIKE THAT! The disaster
that happens in cryptography is secret, and so we will keep riding
that dirg. Consequently, we will have the same disaster (without
really experiencing it), over and over again. The dirg never gets
built right because we don't know where it went wrong. And people use
it anyway, because they "trust" it.
>You are trying to tell me everything engineers do is flawless? Shaw-
>right.
Nonsense. Never said that, never tried to tell you that.
When we design and use normal things, we can tolerate errors because
we see the ultimate results. If the results are not what we want, we
can do something about it.
In cryptography nobody gets to see the ultimate results: We cannot
know if our information is hidden from secret opponents. We don't
know if problems exist, so we cannot fix them. And the "we" part of
this includes everybody: both amateurs and experts.
>There is some science behind cryptography whether you want to believe
>it or not.
Nonsense. I have never said that there is no science behind
cryptography. Many things used in cryptography can be measured, and I
have personally measured and reported on some of them. Many things in
cryptography can be designed to specification, and I have reported on
some of those as well. Instead it is the unsupported belief in cipher
strength which is unscientific.
Science does not require belief. Indeed, that is the whole point. It
is non-science which requires belief, and that is what we have when we
trust some cipher: a belief without supporting evidence.
---
Terry Ritter [EMAIL PROTECTED] http://www.io.com/~ritter/
Crypto Glossary http://www.io.com/~ritter/GLOSSARY.HTM
------------------------------
From: Mike Rosing <[EMAIL PROTECTED]>
Subject: Re: (May 11, 2000) Cipher Contest Update
Date: Mon, 15 May 2000 12:22:31 -0500
Runu Knips wrote:
>
> Adam Durana wrote:
> > But I think when someone publishes a
> > cipher for analysis, they are saying that the only attack they can come up
> > with is brute force. Any attack better than that would be a break through.
> > So if an attack arises that can recover the key or plaintext faster than
> > brute force, I think that attack should get the cipher removed from the
> > listing. Keep in mind this is a contest of cipher design.
>
> I disagree with that definition. RC6, for example, accepts keys
> of any size. It is quite unfair to state that it is therefore
> broken by definition.
I think "much faster" than brute force would be a better term for
"break".
For example, if the key size is n bit, then we might say "much faster"
is 2^(n/2). You could also draw the line 2^(2n/3). It doesn't really
matter too much, but if n ~ 1000 and you say it's "broken" with 2^(n-10)
plaintext-ciphertext pairs, that's not useful.
I really appreciate the updates on the contestants!
Patience, persistence, truth,
Dr. mike
------------------------------
From: Mok-Kong Shen <[EMAIL PROTECTED]>
Subject: Re: Definition of "Broken" Cipher
Date: Mon, 15 May 2000 20:12:36 +0200
Tom St Denis wrote:
> No you are wrong, single des is hopelessly useless now. The key is
> much too small, it's an ugly algorithm, not to mention slow.
>
> And if you reply 'password hash' you are wrong, MD5 or SHA-1 is better
> suited for that task too.
I suppose it's almost sort of an philosophical issue. One has to keep
one's view a bit wider and recognize that there are all sorts of crypto
applications with different kinds of security and affordable resource
and cost requirements. To exaggerate, if one wants to keep one's love
letters from the eyes of a 10 year old brother, then rot13 is probably
more than good enough. In crypto circles different people often have
a pre-conception of a minimum security requirment of encryption
algorithms, based on the type of applications one is particularly
interested in and on one's experiences and subjective judgements.
It's not a too far fetched analogy that often people of different
religious backgrounds are getting together to talk. If one is aware
of this fact and also of the fact that a scientifically rigorous measure
of strength of crypto algorithms is yet to be discovered, I suppose
one will tend to be a bit more 'liberal' in most disputes. (In fact in
my humble opinion there are lots of essential issues in crypto in
which we lack knowledge and are unlikely to gain true knowledge
at all.)
M. K. Shen
------------------------------
Crossposted-To: talk.politics.crypto,sci.answers,news.answers,talk.answers
Subject: Cryptography FAQ (01/10: Overview)
From: [EMAIL PROTECTED]
Reply-To: [EMAIL PROTECTED]
Date: 15 May 2000 19:00:09 GMT
Archive-name: cryptography-faq/part01
Last-modified: 1999/06/27
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.
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.
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.
1999: There is a project underway to reorganize, expand, and update the
sci.crypt FAQ, pending the resolution of some minor legal issues. The
new FAQ will have two pieces. The first piece will be a series of web
pages. The second piece will be a short posting, focusing on the
questions that really are frequently asked.
In the meantime, if you need to know something that isn't covered in the
current FAQ, you can probably find it starting from Ron Rivest's links
at <http://theory.lcs.mit.edu/~rivest/crypto-security.html>.
If you have comments on the current FAQ, please post them to sci.crypt
under the subject line Crypt FAQ Comments. (The crypt-comments email
address is out of date.)
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
------------------------------
Crossposted-To: talk.politics.crypto,sci.answers,news.answers,talk.answers
Subject: Cryptography FAQ (02/10: Net Etiquette)
From: [EMAIL PROTECTED]
Reply-To: [EMAIL PROTECTED]
Date: 15 May 2000 19:00:11 GMT
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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