[Standards] OMEMO and Olm

Remko Tronçon remko at el-tramo.be
Thu May 25 06:04:17 UTC 2017

On 24 May 2017 at 22:55, Andreas Straub <andy at strb.org> wrote:

> Yes, it's true that there's currently no such thing for XEdDSA, but is
> this actually a concrete problem for anyone?

Yes. I obviously can't speak for all the other clients that currently don't
support OMEMO, but for Swift, XEdDSA is blocking OMEMO support for both
technical and legal reasons.

>  implementing this yourself really isn't that complex. You can re-use
> existing EdDSA code, all you need to do is write the key conversion code
> yourself, for which there is pseudo-code in the standard, which maps fairly
> directly to well-known mathematical for which you can also re-use existing
> code. The main novel idea in XEdDSA is resolving an ambiguity in the
> conversion by forcing a sign bit to 0, and that's about it.

I think this is oversimplifying things. It's the same as saying
implementing DH yourself is also fine, because it's just taking the modulo
of 2 integers. Also, "reusing existing code" is also not something every
piece of software takes lightly.

> I just don't see the major implementations switching over any time soon

I have serious doubts that at least one of them won't have to do *some*
significant work to get rid of the libsignal dependency to be legally in
order, which will mean implementing the ratchet and XEdDSA itself (unless a
library emerges that implements this all from scratch).

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