Best practice for periodic key change?

Hauke Laging mailinglisten at
Tue May 10 03:42:47 CEST 2011

Am Montag, 9. Mai 2011, 19:51:12 schrieb MFPA:

> Could that be a form of attack? Bob and Mallory sign a contract of
> some kind - it transpires the contract benefits Bob - Mallory tries to
> make it look as if Bob had not signed.

That would not work for several reasons which arise not from technical aspects 
but the circumstances:

a) Usually the contract mentions the partners. Mallory would have to claim 
that somebody else had signed that though that obviously does not make any 
sense. Furthermore this other one would deny that.

b) It would be obvious that the secret key of the subkey has been stolen. That 
would be a huge risk for the one who has stolen it. He would have to stand up 
in public and state: "Only two people can have stolen the key. One of them is 
me." I am not experienced with criminals but I really doubt that this sounds 
interesting to them.

c) Mallory cannot have created signatures before he stole the key. Bob usually 
has created a lot. Everyone who claims to have seen a signature of the key in 
question by Mallory  before the (probably unknown) date of theft is at serious 
risk to be proven to have lied in court. This would be possible with very new 
keys only.

> There is a third way: amend the law so that the Web of Trust is used
> instead of the CAs.

This is not about the source of trust IMHO. I think that the major aim of the 
law is to prevent the stealing of keys because that would reduce the trust in 
digital signatures in an amount a modern society cannot afford. Thus the law 
requires hardware protection. Whether a hardware-protected key is certified by 
a CA or (strongly enough) by a WoT is less important.

PGP: D44C 6A5B 71B0 427C CED3 025C BD7D 6D27 ECCB 5814
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