Cryptography March 2006

cryptography@lists.squeakfoundation.org

3 participants
4 discussions

Notification of publicly available cryptography code
by Ron Teitelbaum 28 Nov '06

28 Nov '06

Notification of publicly available cryptography code: Cryptography code and access to a repository for continuing development will be made publicly available on or after Monday Jan 9th 2006 as part of the Open Source Squeak Project (www.squeak.org <http://www.squeak.org/> ). The code can be accessed two ways. Either through www.squeakSource.com <http://www.squeaksource.com/> in the cryptography project or through the squeak software itself. The location for the Squeak Montecello repository using HTTP accessed through the Squeak software is: MCHttpRepository location: 'http://kilana.unibe.ch:8888/Cryptography' user: '' password: '' Thank you, Ron Teitelbaum Squeak Cryptography Team Leader

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Rijndael class>>#keySize
by Chris Muller 24 Mar '06

24 Mar '06

Hellooooooooooo... (It's been pretty quiet here). I would like to propose an increment to Rijndael's keySize as recommended in Practical Cryptography. From Chapter 4, section 5.8 (p. 65): "A 128-bit key would be great except for one problem: collision attacks. Time and time again we find systems that can be attacked by a birthday attack or a meet-in-the-middle attack. We know these attacks exist." ... "Design rule 3. For a security level of n bits, every cryptographic value should be at least 2n bits long." ... "For 128-bit security we really want to use a block cipher witha block size of 256 bits, but all the common block ciphers have a block size of 128 bits." ... "Still, at least we can use the large keys that all AES candidate block ciphers support. Therefore: use 256-bit keys!" (I hope I don't get in trouble for quoting this much text). Furthermore, later on in chapter 22 about securing long-term secrets with passphrases, it recommends to "salt and stretch" the passphrase to a 256-bit value and use that to encrypt your secrets (i.e., keyring). The only way Rijndael can do is with a keySize of 256 bits. If anyone objects, please let me know, otherwise I will post this change in the near future. Thanks, Chris

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BlockCipher mode tests, fixes, enhancements
by Chris Muller 08 Mar '06

08 Mar '06

Hi, just a note to let you know of some improvements I've just committed to our repository. Cryptography-Core - All four BlockCipher modes are fixed-up and working (CFB should be verified). - Added ability for BlockCiphers to encrypt and decrypt arbitrary-length ByteArray's. - When using the non-streaming cipher modes (CBC and CFB), proper padding of the ByteArray's should be the responsibility of the BlockCipher, not the user (developer). Therefore, #encrypt: applies the "option 2" padding scheme specified by Ferguson and Schneier in 'Practical Cryptography', p. 68-69. - Can also encrypt/decrypt from:to: positions in an existing ByteArray. - Streaming modes (CTR and OFB) are supported as stream ciphers, ByteArray's can be any size and no padding to the next-larger block is performed or needed. Cryptography-Tests - Created tests for all BlockCipher modes, by generalizing the CTR test. They all now run the same (semi-robust) test. - Separate test conditions ensure streaming modes work properly. - Separate encrypt/decrypt ByteArray tests are included for all BlockCipher modes. More to come.. - Chris

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Niels Ferguson, Bruce Schneier. "Practical Cryptography"
by Chris Muller 06 Mar '06

06 Mar '06

How's everybody doing around here? I wanted to let you know, thanks to Tony, Ron, Cees and Matthew's feedback I've gone back to the drawing board to improve my crypto knowledge. After having battering-rammed my brain through most of Alfred J. Menezes, Paul C. van Oorschot and Scott A. Vanstone "Handbook of Applied Cryptography", I then picked up Niels Ferguson and Bruce Schneier's "Practical Cryptography" last week and have practically inhaled the first half of it in one breath. So easy and refreshing. Most of the books and papers I have read to this point are from the ivory tower, mostly oblivious to real-world practical security issues, especially that of human comprehension and error. Worse, even after working through some of these difficult papers to get one gold "implementation nugget" I then find other material that contradicts it! For example, the envelope composition issue (MAC-then-encrypt vs. encrypt-then-MAC).. So what's one to do, just give up? That's not an option for me, I have to move forward. I spoke with a couple of security experts at C5 and they agree with Schneier, "Cryptography is hard" and "no one can know everything about it." Therefore, at some point, I have to choose to trust some information source and go with it. I've decided to make it this 2003 book because: 1) everyone, including those on this list, seem to acknowledge Schneier as an expert 2) the book is written (as it directly claims to be) for the purpose of implementing secure crypto systems with focus on real issues. 3) seems to, more than any other source I've come across, acknowledge real-world implementation issues regarding crypto; including factoring human-frailty into the security equation (i.e., problems such as complexity). I like and agree with this philosophy. This book (purportedly) gives the average crytologist-wannabe the advice necessary to implement secure protocols. One idea of the book is to throw away mathematical interactions between the crypto primitives that permit certain kinds of attacks. Just a few interactions between primitives, assuming you're aware of them at all, quickly explode into many permutations very hard-to-analyze, hard-to-remember, and essentially insecure because of the hideous complexity. They therefore describe how to implement "ideal" primitives that do not suffer from these weaknesses. These implementations are typically slower than their non-ideal counterparts, but the authors claim the idea is to put security first because "there are enough fast, insecure systems out there.." So far, I really like this book and its philosophies. Has anyone else read the book? Cheers, Chris

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Cryptography March 2006