[Cryptography] In the face of "cooperative" end-points, PFS doesn't help

Jerry Leichter leichter at lrw.com
Sun Sep 8 22:39:54 EDT 2013

On Sep 8, 2013, at 7:16 PM, james hughes wrote:
> Let me suggest the following. 
> With RSA, a single quiet "donation" by the site and it's done. The situation becomes totally passive and there is no possibility knowing what has been
> read.  The system administrator could even do this without the executives knowing.
An additional helper:  Re-keying.  Suppose you send out a new public key, signed with your old one, once a week.  Keep the chain of replacements posted publicly so that someone who hasn't connected to you in a while can confirm the entire sequence from the last public key he knew to the current one.  If someone sends you a message with an invalid key (whether it was ever actually valid or not - it makes no difference), you just send them an update.

An attacker *could* sent out a fake update with your signature, but that would be detected almost immediately.  So a one-time "donation" is now good for a 
week.  Sure, the leaker can keep leaking - but the cost is now considerably
greater, and ongoing.
							-- Jerry

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