On Feb 27, 2007, at 9:08 PM, Jim Fenton wrote:
My overall inclination right now is that trying to distinguish a
message that definitely fails SSP from a message that has an
unknown SSP (because the verifier doesn't know how to verify it) is
putting too fine a point on SSP. The "unknown SSP" case should
just be treated as "fails SSP" and the signer should be cajoled
into providing useful signatures.
There is the what-if-no-signature policy record, and the what-if-
deprecated policy parameter that can be placed within the key record.
By adding a deprecation assertion that essentially describes the
desired parameter that should be within a companion signature, then
this defeats a downgrade attack without any additional transactions
requesting a what-if-no-signature policy record, or any change made
to the current structure.
All that is needed to ensure a downgrade attack can be defeated in
the future would be to define the deprecation assertion within the
existing key.
This might be as simple as:
d=<tag>/<companion-parameter>[:...];
-Doug
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