Hi Remko,

So just for the record (because you didn't answer that question from my 
previous mail):
This is only an implementation detail and has no relevant influence (aka, at 
most constant factor) on the cryptographic properties?

When changing the identity keys to Ed, will that mean that existing 
fingerprints will become invalid? These keys have been printed and/or put on 
websites that are not easily editable, so this should be considered. Just the 
fact that you can convert the keys doesn't mean that the fingerprints can stay 
valid.
If I understand you right, you want to implement OMEMO in a not 
downwards-compatible manner and thus won't be able to show/compare the old 
fingerprints?

Also, as you seem to be very concered about implementation details, you are 
aware of the fact that libsignal is available in multiple languages/platforms 
whereas libsodium is native code only, so there are some cases where you can 
not easily drop in the code from libsodium.

Ignat

"Remko Tronçon" <[email protected]> wrote:
Hi Ignat,

can you please describe the concrete benefits of your approach?

It gets rid of the non-standard XEdDSA dependency, which is blocking me (and 
likely others) in creating independent implementations that don't depend on 
libsignal. (see the other threads for my reasons).
 
The only difference I can spot is that it's more implementation work for those 
that use libsignal (which at this point in time seems to be all 
implementations) and less for libsodium (which happens to not implement many 
other parts of the protocol as well and thus require a lot of work nonetheless).

Libolm implements the rest of the protocol. I used libsodium to prove that 
anyone can create an independent implementation. If you want to use libolm, 
you'd need to change the 3DH to X3DH (same as in the prototype), and pass in an 
extra key (Olm doesn't have signed one-time prekeys).

So it's a little bit of work for libsignal, and a bit more work for libolm. 
It's a compromise.

Remko
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