On Wed, 12 Jan 2005, Sam Hartman wrote:
I do note that you're actually somewhat vulnerable to this replay even
with signed bodies. I go get a free email account from an email
provider with a reasonably good reputation. I send email containing
the spam body I want to some recipient I control that will look good
in to: headers. Now that I've got this signature, I can replay the
message at any envelope recipient I want.
This puts the free email provider in the position of needing to revoke
the key I'm using, but they cannot do that until the other mail signed
with that key has had a chance to flow through the system.
If you implement per-user keys, then revocation of an account can imply
revocation of the key without affecting any innocent bystanders. However
there are efficiency considerations for recipients (how many keys are they
expected to cache, and for how long) and for senders (per-user keys with
low TTLs make joe jobs have a worse effect).
Tony.
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