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OK, rotating the DKIM keys allows someone to send an email and then later claim that the email was a forgery. But the fact that the DKIM keys are rotated is goi

OK, rotating the DKIM keys allows someone to send an email and then later claim that the email was a forgery. But the fact that the DKIM keys are rotated is going to be generally known. So how could this possibly work? Someone comes to you and claims that a particular email was forged. They have no evidence of this forgery and no evidence that someone was even motivated and capable of doing such a forgery. You check and see that DMIM rotation is being done. Wouldn't the fact that there was a system set up specifically to allow someone to send an email and then lie about it make you very suspicious that they had done exactly that? Forwarding an the email to a third party entirely defeats this scheme, doesn't it?

remram 3y ago
> Wouldn't the fact that there was a system set up specifically to allow someone to send an email and then lie about it make you very suspicious that they had done exactly that? Not really, not when people have been arguing for this setup as a best practice for years for whole domains.
joveian 3y ago
The argument is that the system as a whole shouldn't be set up in a way to provide (possible, limited) non-repudiation, similar to how postal mail (at least in the US) doesn't provide non-repudiation. It is not something that most people individually would have a say in how it is set up. Publishing expired DKIM keys wouldn't let you claim to the recipient that the message was forged but would make it harder to convince third parties in some contexts that the message is likely to be authentic. The advantage of deniability is that someone who manages to get one email of yours by any means can't prove to the world that you sent it, which can be an issue with things that are socially considered unfavorable as well as unsympathetic situations like corrupt politicians. There are disadvantages relating to harassment and corruption. The article doesn't mention it but trusted timestamping during the validity of the DKIM key (plus as always having a copy of the public key) preserves the (limited) non-repudiation. Forwarding during the DKIM key validity could potentially work as a reliable timestamp depending on the details of the forwarding.

remram 3y ago

> Wouldn't the fact that there was a system set up specifically to allow someone to send an email and then lie about it make you very suspicious that they had done exactly that? Not really, not when people have been arguing for this setup as a best practice for years for whole domains.

joveian 3y ago

The argument is that the system as a whole shouldn't be set up in a way to provide (possible, limited) non-repudiation, similar to how postal mail (at least in the US) doesn't provide non-repudiation. It is not something that most people individually would have a say in how it is set up. Publishing expired DKIM keys wouldn't let you claim to the recipient that the message was forged but would make it harder to convince third parties in some contexts that the message is likely to be authentic. The advantage of deniability is that someone who manages to get one email of yours by any means can't prove to the world that you sent it, which can be an issue with things that are socially considered unfavorable as well as unsympathetic situations like corrupt politicians. There are disadvantages relating to harassment and corruption. The article doesn't mention it but trusted timestamping during the validity of the DKIM key (plus as always having a copy of the public key) preserves the (limited) non-repudiation. Forwarding during the DKIM key validity could potentially work as a reliable timestamp depending on the details of the forwarding.