Cryptography-Digest Digest #768, Volume #9 Fri, 25 Jun 99 09:13:05 EDT
Contents:
Re: Why Elliptic Curve Cryptosystem is stronger with shorter key length? (Robert
Harley)
Bytes of "truly random" data for PRNG seed. (Benjamin Goldberg)
Re: generated pad for OTP? (fungus)
Re: Bytes of "truly random" data for PRNG seed. ("Douglas A. Gwyn")
Re: Why Elliptic Curve Cryptosystem is stronger with shorter key length? (Medical
Electronics Lab)
Re: one time pad ("Douglas A. Gwyn")
Cryptography FAQ (01/10: Overview) ([EMAIL PROTECTED])
Cryptography FAQ (02/10: Net Etiquette) ([EMAIL PROTECTED])
----------------------------------------------------------------------------
From: Robert Harley <[EMAIL PROTECTED]>
Subject: Re: Why Elliptic Curve Cryptosystem is stronger with shorter key length?
Date: 25 Jun 1999 11:40:03 +0200
Medical Electronics Lab <[EMAIL PROTECTED]> writes:
> No, Koblitz curves [...] These curves have
> structure of 2*prime, 4*prime or 18*prime. For 2 or 4*prime, and
> n large, where's the "extra" structure?
"Structure" covers a lot more than just the number of points over one
field. These curves have many special properties, for instance a
bunch of automorphisms as I mentioned. These properties are a minor
convenience for implementation but a major danger for security.
> After 15+ years of pounding, the basic ECC is still pretty secure.
This is true for most curves, but false for many of the special cases
that have been proposed. Special cases are dangerous. What's hard to
understand about that?
Bye,
Rob.
------------------------------
From: Benjamin Goldberg <[EMAIL PROTECTED]>
Subject: Bytes of "truly random" data for PRNG seed.
Date: Fri, 25 Jun 1999 07:33:41 -0400
The seed generator used in java.security.SecureRandom says that it
"has not been thoroughly studied or widely deployed." Does anyone know
how I could go about verifying that the bytes provided by that method are
"truly random," in the sense that they are usable for cryptographic
purposes?
Incidentally, in case anyone is interested, I have my own implementation
of the SeedGenerator at
http://www.rpi.edu/~goldbb/src/java/util/SeedGenerator.java
which uses threads in such a way as to avoid causing the one-second
freeze-up when the class is loaded that the version in java.security does.
Ben Goldberg
--
The fountain code has been tightened slightly so you can no longer dip objects
into a fountain or drink from one while you are floating in mid-air due to
levitation.
Teleporting to hell via a teleportation trap will no longer occur if the
character does not have fire resistance.
- README file from the NetHack game
------------------------------
From: fungus <[EMAIL PROTECTED]>
Subject: Re: generated pad for OTP?
Date: Fri, 25 Jun 1999 15:12:19 +0200
Benjamin Goldberg wrote:
>
> If I have some secret sequence of bytes [as in a session key] and use this
> sequence as a seed for a psuedo random number generator, and use the
> output of this PRNG as my pad, how easy/hard is it to decrypt data that
> has been XORed with this generated pad? While I assume that it depends on
> the PRNG
Correct.
> are there generators that are "crytpographically strong?"
Yes. RC4 springs to mind, or you could do a web search for the
"Blum Blum Shub" (nice name!). You can also use a block cipher
like DES in feedback mode (keep re-encrypting the same block of
data).
> Java offers the class 'java.secuity.SecureRandom' which it *claims* is
> "crytpographically strong," but I don't know enough about cryptography to
> figure out how accurate that claim of strength is.
>
I assume the people who made Java do know enough to claim this.
> The "SecureRandom" generator produces 20 psuedo-random bytes at a time, by
> incrementing a 64-bit counter, and using a SHA-1 digest on that counter
> and a seed. While I know you can't reconstruct a message directly from a
> digest, we have, for many values of the counter, the digest of a known
> value followed by an unknown value... could one concievably trace the path
> of the bits of the counter through to the digest, and compute the next
> digest in the sequence? The counter of course starts at 0, and is
> incremented every time 20 bytes of psuedo-random data has been used.
>
No. If any part of the value is unknown then you can't predict the hash
value. Although you don't mention the size of the unknown data, this
algorithm sounds reasonable as a crypto random number generator.
Your security against a brute-force attack obviously depends on the size
of the secret data.
--
<\___/>
/ O O \
\_____/ FTB.
------------------------------
From: "Douglas A. Gwyn" <[EMAIL PROTECTED]>
Subject: Re: Bytes of "truly random" data for PRNG seed.
Date: Fri, 25 Jun 1999 12:30:27 GMT
Benjamin Goldberg wrote:
> how I could go about verifying that the bytes provided by that method
> are "truly random," in the sense that they are usable for
> cryptographic purposes?
That depends on such things as: who your adversary is.
------------------------------
From: Medical Electronics Lab <[EMAIL PROTECTED]>
Subject: Re: Why Elliptic Curve Cryptosystem is stronger with shorter key length?
Date: Thu, 24 Jun 1999 12:15:56 -0500
Robert Harley wrote:
> Elliptic curves defined over GF(2) i.e., "Koblitz" curves, most
> certainly do have a lot of extra structure.
No, Koblitz curves over GF(2^n) have the form y^2 + xy = x^3 + gx + g'
where g and g' are related (usually 1 or 0). These curves have
structure of 2*prime, 4*prime or 18*prime. For 2 or 4*prime, and
n large, where's the "extra" structure?
> 18 months ago you would have said that there was no reduction in
> safety, and I would have replied that it was entirely plausible that
> some speedups would be found for those curves.
>
> Then several groups of people found the sqrt(m) speedup so now you're
> saying there is only a small reduction in safety, to which I reply
> that it is entirely plausible that there will be much greater speedups
> found in a year or in ten years.
>
> Using curves with *any* extra structure is a bad idea, as has been
> confirmed over and over.[...]
But now you are talking about just discussed academic crypto. Sure,
you have to watch it closely. After 15+ years of pounding, the
basic ECC is still pretty secure.
Now, if I was really paranoid, I'd have to agree with you that really
knowing the curve parameters, and picking "random" curves is superior
security. However, as a practical case, most people have far worse
*security* problems than they have *cryptography* problems, so the
use of CM or multiple field (GF(2^(m*d)) type) is perfectly useable.
But this gets off into engineering and marketing problems, and has
little to do with the math.
Patience, persistence, truth,
Dr. mike
------------------------------
From: "Douglas A. Gwyn" <[EMAIL PROTECTED]>
Subject: Re: one time pad
Date: Fri, 25 Jun 1999 12:27:19 GMT
[EMAIL PROTECTED] wrote:
> This is called numerology.
Numerology is slightly different, but it's a related activity.
As an example of a coincidence, look at the 6th column on the second
page of Kryptos: HEADER AND EI(ght?)
------------------------------
From: [EMAIL PROTECTED]
Crossposted-To: talk.politics.crypto,sci.answers,news.answers,talk.answers
Subject: Cryptography FAQ (01/10: Overview)
Date: 25 Jun 1999 13:03:14 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: 25 Jun 1999 13:03:27 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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