On May 15, 6:05pm, Peter Trei wrote:
40 bit encryption is a bad joke = it would take about 2 min on this machine for 40 bit DES
Yes, 40 bit encryption is a joke, but one shouldn't extrapolate exponontially between 56 bit DES and 40 bit encryption. The work factor will not be less by a factor of 1/65536, but rather in the same ballpark. DES is generally faster to search than other ciphers (5-10 times faster than RC5), so if the 40 bit encryption is not with DES, 10 minutes would be a more accurate estimate. As for 40 bit DES, nobody uses DES as is with 16 bits of the key zeroed out. What is more likely is something like CDMF. A brute force attack on CDMF has about four times the work the factor of (56 bit DES / 65536). Again 10 minutes appear more accurate. Which is not to say that we are not discussing a joke. And talking about Wiener machines, they are much faster on DES than most other symmetric ciphers, especially something like RC5, which had reducing the efficiency of hardware crackers as a design goal. So, one should be careful about extrapolating from DES key search rates. -- Anil Das