6.3
11. The Protocol MUST NOT be required to be invoked if a valid first party
signature is found.
Should be:
The Protocol MUST NOT be required to be invoked if a valid first party
signature that satisfies the cryptographic criteria of the recipient is found.
If I look at the email and find a satisfactory signature I am done. If I don't
find any signature at all *or I find only a weak signature* I need to look at
the policy.
Otherwise the requirements of 5.7 are unmet.
This requirement only starts to have real effect when we have a serious enough
compromise of SHA or RSA1024 to mean that verifiers would reject weak
signatures. I don't expect to get there until 2015 but I do expect to get there
eventually.
Also I would like to reword 12:
[PROVISIONAL] A domain holder MUST be able to publish a Practice which
enumerates the acceptable cryptographic algorithms for signatures purportedly
from that domain.
To be
12a [PROVISIONAL] A domain holder MUST be able to publish a Practice which
specifies the acceptable application of cryptographic algorithms for signatures
purportedly from that domain.
12b [PROVISIONAL] A domain holder MUST be able to publish a Practice which
specifies the application of multiple signatures with different cryptographic
algorithms for messages purportedly from that domain.
The difference here is key to the distinction between my proposal and the
existing one. A mere enumeration of the acceptable algorithms does not allow
the upgrade/downgrade attack to be effectively defeated. Merely saying 'I
support SHA-256' does not in fact strengthen the policy.
Also the term 'enumeration' expresses the assumption that the algorithms will
be listed in the policy record. I don't think they should go there. The proper
place for them is in the key record. This avoids the need to duplicate the
information and is in any case necessary to meet requirement 11 which can only
be met if the key records effectively enumerate the set of acceptable
algorithms.
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