Re: [quicwg/base-drafts] token-based greasing / initial packet protection (#3166)

[Marten Seemann <[e-mail]>]

marten-seemann commented on this pull request.

I like this approach, thanks for writing this up @kazuho.

While greasing helps against a passive attacker, it only helps against an active attacker if the set of of alternative version numbers is large, so large that the attacker can't obtain all alternatives by connecting to the server (a reasonable number of times).

An easy way to do this is to derive alternative version numbers by applying a transformation on the version number, e.g. use every number that fulfils `hash(salt || alternative version number) mod 4 == 0` as an alternative. This would generate a huge set of alternative version numbers. In that case, the server would probably also want to encode the initial salt into the token.



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