Re: [quicwg/base-drafts] CID's should be compared in constant time (#2477)

Martin Thomson <> Sun, 17 February 2019 19:46 UTC

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From: Martin Thomson <>
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Subject: Re: [quicwg/base-drafts] CID's should be compared in constant time (#2477)
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The "secret" here is a connection ID.  Something we put in packets without encryption.

If the cost is that you can force a server to attempt to decrypt packets, that's relatively easy to do by other means.  If the point is to attribute that pointless work to others, that's maybe a tiny bit interesting as a DoS vector, but it seems to me like this isn't that useful a thing to document.

The underlying assumption here has always been that decryption, successful or otherwise, is cheap enough that an attacker ends up spending more resources in sending the packet than the defender does in discarding them.  That's not completely true as decryption isn't free, but the cost/benefit to an attacker is very low and - relevant to our current effort - it is extremely difficult to defend if you assume differently. From that perspective, I don't think we should do anything about this.

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