On 13 Nov 2013 17:01, "Fedor Brunner" <fedor.brun...@azet.sk> wrote: > There is good comparison website for key sizes recommendations: http://www.keylength.com/en/compare/ > Enter the year until when your system should be protected and see the Discrete Logarithm Group column. >
Yes, that site is very nice. > The scenario I thinking of is "record now and decrypt later", the 1024 bit DH could protect your message for next year, but if the attacker makes a copy of your conversation now, he can later (for example in 5-10 years with much stronger hardware) break DH easily. There is communication which should be protected even for long time, for example: business strategies, client-lawyer communication, patent information. Yes, I agree that some considerations might raise it, but I think the case for making PFS last as long as the assymmetric identity algorithm is pretty weak in general. To decrypt all communications using 1024-bit DH over a year is likely to be vastly bigger than for one conversation; the same isn't true for RSA, for example, where you could solve the private key once. It is, I agree, the obvious attack point for a single conversation, but you're still talking in terms of vast computational resources for all the traffic. Bear in mind that if we had used 768-bit DH two years ago in PFS, I'd still have only got as far as two of your sessions - I'd have to be pretty good on my targetting to get the information I wanted at that rate.
