[messaging] Provable (private) conversation while allowing (somewhat) precise redaction

Tamme Schichler tammeschichler at googlemail.com
Thu Oct 9 09:08:17 PDT 2014

Am 07.10.2014 um 02:25 schrieb Dave Crocker:
> On 10/6/2014 4:44 PM, Tamme Schichler wrote:
>> The problem is that B has a history of lying
>> about such conversations, so A wants to be able to prove as much as
>> becomes necessary to deflect allegations, but also little as possible to
>> protect the privacy of either side or third parties (or the other way
>> around, as usual the solution would ideally be symmetric).
> Sounds like a classic requirement for Non-Repudiation of Recipient:
>    http://www.cse.scu.edu/~tschwarz/coen351_06/PPtPre/Nonrepudiation.ppt
>    http://ccr.sigcomm.org/archive/1996/jan96/ccr-9601-coffey.ps
> d/

Thanks for these links, the proofs of receipt are definitely something I
need to look into. Ideally it should be simultaneous, but I don't know a
scheme that can do that without a witness. (I think. I remember reading
about some Bitcoin-related schemes involving forcing someone to reveal a
secret in the process of acquiring something, but that may just have
used the block-chain for witnessing it instead.)

Since I'm thinking about a chat protocol it could be feasible to use
some kind of alternating system that prevents the conversation from
progressing without the previous proofs. Being able to use a
non-repudiation server instead would definitely be better though.

Unfortunately I don't know any existing services that can do this
programmatically, but it should be easy enough to allow someone to host
one on-the-fly if I get around to implementing the main protocol.


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