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resistance to swamping attacks.
Ref: Your note of Fri, 27 Sep 1996 11:13:48 +0200 (MET DST) (attached)
> The cookie approach certainly does this. The idea [expense
> for the sender, cheap verification for the receiver] is interesting, but
> fails if precomputing can happen on the sending side. Others?
>
> Germano
To avoid the benefits of pre-computing you need to have some kind of
"fresh challenge" sent from receiver to sender. This requires an additional
round-trip (like Karn's cookies do).
If one does not add the round trip, one can still make the life of the
sender somewhat harder by mixing into the "hard" problem to be solved (by
the sender) both the receiver's IP address and the time of the connection.
Precomputation is then possible but the product of that computation must
be used with a particular host and withing a time limit.
Hugo
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