Management of signature keys for government

[Paul Leyland]

> This emphasises the usefulness of a secure time-stamping service as a way
> of providing evidence of the times of signature of the contract and the
> delivery of the revocation (although such a service is not the only way of
> proving these things).

There are those who would disgree strongly and as a matter of principle,
They point out that it is very difficult, if not impossible in principle, to
get differing observers to agree on the time of an event.  Just as in
relativity, the concept of simultaneity is very slippery when considering
networked systems (and especially so for off-line systems).  The best one
can often do (again as in relativity) is establish a causal relationship
between two events and one is forced to regard acausal events as occuring in
either order or simultaneously depending on which observer's opinion is
requested.  The SPKI crowd have debated this point at great length.  It is
for reasons such as these that SPKI certificates have explicit expiry dates,
use only local names, and so on.  The full story is far too long for me to
go into here.

What the time-stamping service really does, according to this picture, is
not to provide evidence of the *time* of an event, but to establish a causal
relationship between certain events.

Paul