[Cryptography] Crypto best practices

[Jerry Leichter]

> Another interesting recommendation: "Tools should perform key exchange exactly once per connection. Many algorithms have weaknesses during key exchange and the volume of data expected during a given connection does not meet the threshold where a re-key is required.xiii To reiterate, re-keying is not recommended.” Footnote xiii adds "The exact nature of which algorithms are weak at this stage is highly classified....
The only thing this brings immediately to mind is related key attacks.  Though if your re-keying mechanism allows related-key attacks you have other problems.

Anyone have any insight into just what they're referring to?  It could be extremely significant, given that forward security relies on very frequent re-keying.

                                                        -- Jerry