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Is Google failing DKIM keys shorter than 512 bits?

Today’s Wednesday question comes from Andrew B. and got pushed to Thursday so I could check a few more facts.

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How long is your DKIM key?

While we were at M3AAWG, Wired published an article talking about how simple it was to crack DKIM keys. I didn’t post about it at the time because it didn’t really seem like news. DKIM keys smaller than 1024 are vulnerable and not secure and the DKIM spec does not recommend using keys smaller than 1024. When I asked the DKIM-people-who-would-know they did tell me that the news was that the keys had been cracked and used in the wild to spoof email.
Fair enough.
If you are signing with DKIM, use a key 1024 or longer. Anything shorter and your risk having the key cracked and your mail fraudulently signed.
This morning M3AAWG published recommendations on keeping DKIM keys secure.

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DMARC: an authentication framework

A new email industry group was announced this morning. DMARC is a group of industry participants, including large senders, large receivers and relevant intermediaries working on a framework to reduce the harm from phishing.
DMARC is working on a standard to allow senders to publish sending policies and receivers to act on those policies. Currently, senders who want receivers to not deliver unauthenticated email have to negotiate private agreements with the ISPs to make that happen. This is a way to expand the existing programs. Without a published standard, the overhead in managing individual agreements would quickly become prohibitive.
It is an anti-phishing technique built on top of current authentication processes. This is the “next step” in the process and one that most people involved in the authentication process were anticipating and planning for. I’m glad to see so many big players participating.
 

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