### Re: MD6 withdrawn from SHA-3 competition

At 10:39 AM -0700 7/4/09, Hal Finney wrote: But how many other hash function candidates would also be excluded if such a stringent criterion were applied? Or turning it around, if NIST demanded a proof of immunity to differential attacks as Rivest proposed, how many candidates have offered such a proof, in variants fast enough to beat SHA-2? Several hash candidates have proofs against differential attacks but only four with such proofs are faster than SHA-2 (Edon-R, Shabal, Cheetah and Keccak). But according to http://eprint.iacr.org/2008/511.pdf Keccak and Cheetah in 32-bit mode are not actually faster than SHA-2. C.K.F. Lin - The Cryptography Mailing List Unsubscribe by sending unsubscribe cryptography to majord...@metzdowd.com

### Re: MD6 withdrawn from SHA-3 competition

Paul Hoffman wrote: At 10:39 AM -0700 7/4/09, Hal Finney wrote: But how many other hash function candidates would also be excluded if such a stringent criterion were applied? Or turning it around, if NIST demanded a proof of immunity to differential attacks as Rivest proposed, how many candidates have offered such a proof, in variants fast enough to beat SHA-2? The more important question, and one that I hope gets dealt with, is what is a sufficient proof. We know what proofs are, but we don't have a precise definition. We know what a proof should look like, sort of. Ron and his crew have their own definition, and they can't make MD6 work within that definition. But that doesn't mean that NIST wouldn't have accepted the fast-enough MD6 with a proof from someone else. Mathematicians have a precise definition of what a proof is, thanks to logicians like David Hilbert and Kurt Goedel. But people in all disciplines have a terrible time formulating problems, and remembering the conditions under which a statement was proved. They also quote theorems incorrectly, and errors propagate through the less well-reviewed parts of the literature. -- Josh Rubin jlru...@gmail.com - The Cryptography Mailing List Unsubscribe by sending unsubscribe cryptography to majord...@metzdowd.com

### Re: MD6 withdrawn from SHA-3 competition

At 10:39 AM -0700 7/4/09, Hal Finney wrote: But how many other hash function candidates would also be excluded if such a stringent criterion were applied? Or turning it around, if NIST demanded a proof of immunity to differential attacks as Rivest proposed, how many candidates have offered such a proof, in variants fast enough to beat SHA-2? The more important question, and one that I hope gets dealt with, is what is a sufficient proof. We know what proofs are, but we don't have a precise definition. We know what a proof should look like, sort of. Ron and his crew have their own definition, and they can't make MD6 work within that definition. But that doesn't mean that NIST wouldn't have accepted the fast-enough MD6 with a proof from someone else. --Paul Hoffman, Director --VPN Consortium - The Cryptography Mailing List Unsubscribe by sending unsubscribe cryptography to majord...@metzdowd.com

### Re: MD6 withdrawn from SHA-3 competition

On Sat, 2009-07-04 at 10:39 -0700, Hal Finney wrote: Rivest: Thus, while MD6 appears to be a robust and secure cryptographic hash algorithm, and has much merit for multi-core processors, our inability to provide a proof of security for a reduced-round (and possibly tweaked) version of MD6 against differential attacks suggests that MD6 is not ready for consideration for the next SHA-3 round. But how many other hash function candidates would also be excluded if such a stringent criterion were applied? Or turning it around, if NIST demanded a proof of immunity to differential attacks as Rivest proposed, how many candidates have offered such a proof, in variants fast enough to beat SHA-2? I think resistance to attacks (note absence of any restrictive adjective such as differential) is a very important property (indeed, one of the basic defining criteria) to demonstrate in a hash algorithm. If someone can demonstrate an attack, differential or otherwise, or show reason to believe that such an attack may exist, then that should be sufficient grounds to eliminate a vulnerable candidate from any standardization competition. In other words, the fact that MD6 can demonstrate resistance to a class of attacks, if other candidates cannot, should stand in its favor regardless of whether the competition administrators say anything about proving resistance to any particular *kind* of attacks. If that does not stand in its favor then the competition is exposed as no more than a misguided effort to standardize on one of the many Wrong Solutions. Bear - The Cryptography Mailing List Unsubscribe by sending unsubscribe cryptography to majord...@metzdowd.com

### Re: MD6 withdrawn from SHA-3 competition

At 11:49 PM -0400 7/3/09, Steven M. Bellovin wrote: Here's the essential paragraph: Thus, while MD6 appears to be a robust and secure cryptographic hash algorithm, and has much merit for multi-core processors, our inability to provide a proof of security for a reduced-round (and possibly tweaked) version of MD6 against differential attacks suggests that MD6 is not ready for consideration for the next SHA-3 round. At 10:12 AM + 7/4/09, Brandon Enright wrote: It wasn't entirely clear to me if it really was withdrawn. Ron Rivest posted on behalf of the MD6 team some thoughts on MD6 performance and specifically suggested/requested that NIST ask for submitted algorithms to be provably resistant to differential attacks. I agree more with Brandon than with Steve, but who knows. I read Ron's message as a challenge to NIST about whether or not NIST would really rely on the proofs. It was clear they didn't want to withdraw MD6, but that they felt like they had to because of the speed requirement. --Paul Hoffman, Director --VPN Consortium - The Cryptography Mailing List Unsubscribe by sending unsubscribe cryptography to majord...@metzdowd.com

### Re: MD6 withdrawn from SHA-3 competition

Rivest: Thus, while MD6 appears to be a robust and secure cryptographic hash algorithm, and has much merit for multi-core processors, our inability to provide a proof of security for a reduced-round (and possibly tweaked) version of MD6 against differential attacks suggests that MD6 is not ready for consideration for the next SHA-3 round. But how many other hash function candidates would also be excluded if such a stringent criterion were applied? Or turning it around, if NIST demanded a proof of immunity to differential attacks as Rivest proposed, how many candidates have offered such a proof, in variants fast enough to beat SHA-2? Hal Finney - The Cryptography Mailing List Unsubscribe by sending unsubscribe cryptography to majord...@metzdowd.com

### Re: MD6 withdrawn from SHA-3 competition

On Thu, 2 Jul 2009 20:51:47 -0700 Joseph Ashwood ashw...@msn.com wrote: -- Sent: Wednesday, July 01, 2009 4:05 PM Subject: MD6 withdrawn from SHA-3 competition Also from Bruce Schneier, a report that MD6 was withdrawn from the SHA-3 competition because of performance considerations. I find this disappointing. With the rate of destruction of primitives in any such competition I would've liked to see them let it stay until it is either broken or at least until the second round. A quick glance at the SHA-3 zoo and you won't see much left with no attacks. It would be different if it was yet another M-D, using AES as a foundation, blah, blah, blah, but MD6 is a truly unique and interesting design. I hope the report is wrong, and in keeping that hope alive, the MD6 page has no statement about the withdrawl. The report is quite correct. Rivest sent a note to NIST's hash forum mailing list (http://csrc.nist.gov/groups/ST/hash/email_list.html) announcing the withdrawal. Since a password is necessary to access the archives (anti-spam?), I don't want to post the whole note, but Rivest said that they couldn't improve MD6's performance to meet NIST's criteria (at least as fast as SHA-2); the designers of MD6 felt that they could not manage that and still achieve provable resistance to differential attacks, and they regard the latter as very important. Here's the essential paragraph: Thus, while MD6 appears to be a robust and secure cryptographic hash algorithm, and has much merit for multi-core processors, our inability to provide a proof of security for a reduced-round (and possibly tweaked) version of MD6 against differential attacks suggests that MD6 is not ready for consideration for the next SHA-3 round. --Steve Bellovin, http://www.cs.columbia.edu/~smb - The Cryptography Mailing List Unsubscribe by sending unsubscribe cryptography to majord...@metzdowd.com

### Re: MD6 withdrawn from SHA-3 competition

On Thu, 2 Jul 2009 20:51:47 -0700 or thereabouts Joseph Ashwood ashw...@msn.com wrote: Sent: Wednesday, July 01, 2009 4:05 PM Subject: MD6 withdrawn from SHA-3 competition Also from Bruce Schneier, a report that MD6 was withdrawn from the SHA-3 competition because of performance considerations. I find this disappointing. With the rate of destruction of primitives in any such competition I would've liked to see them let it stay until it is either broken or at least until the second round. A quick glance at the SHA-3 zoo and you won't see much left with no attacks. It would be different if it was yet another M-D, using AES as a foundation, blah, blah, blah, but MD6 is a truly unique and interesting design. I hope the report is wrong, and in keeping that hope alive, the MD6 page has no statement about the withdrawl. Joe It wasn't entirely clear to me if it really was withdrawn. Ron Rivest posted on behalf of the MD6 team some thoughts on MD6 performance and specifically suggested/requested that NIST ask for submitted algorithms to be provably resistant to differential attacks. The logic was that MD6 is slow because the high number of rounds is needed in their proof. They won't tweak/submit a version that doesn't meet this requirement of theirs and based on the current contest requirements, they can't be competitive speed-wise without losing their proof of resistance to differential attacks. Unless the contest changes to require such a proof, there is no point in moving MD6 forward. Brandon - The Cryptography Mailing List Unsubscribe by sending unsubscribe cryptography to majord...@metzdowd.com

### Re: MD6 withdrawn from SHA-3 competition

-- Sent: Wednesday, July 01, 2009 4:05 PM Subject: MD6 withdrawn from SHA-3 competition Also from Bruce Schneier, a report that MD6 was withdrawn from the SHA-3 competition because of performance considerations. I find this disappointing. With the rate of destruction of primitives in any such competition I would've liked to see them let it stay until it is either broken or at least until the second round. A quick glance at the SHA-3 zoo and you won't see much left with no attacks. It would be different if it was yet another M-D, using AES as a foundation, blah, blah, blah, but MD6 is a truly unique and interesting design. I hope the report is wrong, and in keeping that hope alive, the MD6 page has no statement about the withdrawl. Joe - The Cryptography Mailing List Unsubscribe by sending unsubscribe cryptography to majord...@metzdowd.com