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Re: [quicwg/base-drafts] Preventing KEY_PHASE bit from being used as a tool to correlate CIDs (#1322)

MikkelFJ <notifications@github.com> Fri, 04 May 2018 08:28 UTC

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Subject: Re: [quicwg/base-drafts] Preventing KEY_PHASE bit from being used as a tool to correlate CIDs (#1322)
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@marten-seemann 
>Is there any limit on how many key updates can safely be done? If not, another option would be to lower the threshold to e.g. 2^16 (this would correspond to roughly 80MB of data transferred). This would ensure that a significant fraction of QUIC connections would do a key update.

Yes, sort of. If there is a 1/N chance of a successfull attack on a key, and you have M keys, the chance is improved to M/N. As I understand this ties more to AES than to GCM and since AES is much harder than GCM, this is not an immediate concern, but too many keys is not a good idea.

See 
1.3 Security Degradation for Multiple Keys

http://www.isg.rhul.ac.uk/~kp/TLS-AEbounds.pdf

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