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Re: [MLS] Proposals for handling concurrent messages

Jeff Burdges <burdges@gnunet.org> Tue, 26 March 2019 15:01 UTC

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Subject: Re: [MLS] Proposals for handling concurrent messages
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> On 23 Mar 2019, at 19:59, M.A.L. Weidner <malw2@cam.ac.uk> wrote:
> Thanks for this, I'll check Ristretto out.  One related concern I have is that I have not yet found any mainstream post-quantum crypto proposals that support key combining.

Just fyi, CSIDH supports composing secret keys, meaning if  CSIDH(A,b) = CSIDH(B,a)  then  CSIDH(A, x . b) = CSIDH(B, x . a)  for some other secret key that both A and B know.  You could do a simple successive multi-way DH too I think, so more CSIDH(CSIDH(B, x), a) etc.

I doubt this helps Causal TreeKEM, but it’s extremely helpful for mixnets.  In fact, mixnets are part of the reason CSIDH was created.  It might help do ART-like constructions and/or protect against malicious updates though.

Jeff

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