The only RSA Secret Key Challenge known to be under active attack at this time is RC5-64, by distributed.net. Last night this reached the 50% mark, having tested 9,225,283,403,065,065,472 keys at the time I write this, over 1331 days. The current rate is over 210 Gkeys/sec - they should complete the keyspace in the next 18 months. See: http://stats.distributed.net/rc5-64/ Way back in the previous millenium, RSA (then Security Dynamics) issued a series of 'secret key challenges', in which prizes were offered for decrypting messages encrypted wish RC5 and DES. http://www.rsasecurity.com/rsalabs/challenges/ <brag-mode:on> I was responsible for getting SDTI to create the challenges, proposing them to Jim Bidzos to complement the long standing RSA factoring contests back in 1996. I was mainly interested in demonstrating that 56 bit DES (then the strongest exportable algorithm) was inadequate, and had created a proof-of-principle DES key-cracker to demonstrate that the goal was achievable. Jim thought this was a good idea, and I was soon collaborating with RSA Labs in the design of the challenges - long before I came to work at SDTI/RSA. The first challenge (40 bit RC5) fell in 3.5 hours, and was soon followed by others, leading up to the 3rd DES challenge in 1999, when distributed.net and the EFF combined to brute force a 56 bit DES key in 23 hours. The success in the attacks on the Secret Key Challenges created facts on the ground exposing the weakness of exportable crypto, and in my opinion were important in causing the relaxation of US export regulations in early 2000 <brag-mode:off>. Peter Trei