Opensc: Add curve25519 support in OpenSC

[alex-nitrokey]

Currently, there is no support for curve25519 in OpenSC. There is support for the curves shown here and here only (as far as I can see). It is possible that there are just not many cards out there that support this curve, but there are people looking out for this curve. So this is a newer version of an old request.

I can not oversee the work that needs to be done to make curve25519 work, therefore I created this issue. I hope for discussion and help. If anyone wants to implement this, I would be happy. Nitrokey can provide free Nitrokey Start devices (equivalent to Gnuk devices, which support curve25519) to test code. The openpgp card driver used by Gnuk is already prepared.

[ya-isakov]

Yubikey with firmware 5.2.3+ is also supporting Ed25519/Curve25519, and these kind of curves are more and more popular.

[Jakuje]

The problem with Ed25519/Curve25519 is that it is not supported in the current version of PKCS #11 specification without vendor specific extension (see the discussion in softhsm PR: https://github.com/opendnssec/SoftHSMv2/pull/324 ). The IDs for these should come in PKCS#11 3.0, but it is not out yet (even though used in SoftHSM: https://github.com/opendnssec/SoftHSMv2/blob/develop/src/lib/pkcs11/pkcs11.h#L889 )

I think I have old yubikey that does not support these keys, but it would be interesting to implement support for these (at least keys -- not sure about the use of the pure curve25519).

[jans23]

@Jakuje If it helps, we could ship you a free Nitrokey Start.

[Jakuje]

@jans23 That would be nice. Please, drop me an email. Unfortunately, I can not estimate when I will be able to work on these, but I would be certainly interested in improving OpenSC in this way.

[Jakuje]

for the record, this is already WIP, but I still do not have anything that can be published as it is touching a lot of things all over the code base, but I hope in coming weeks I will be able to open a PR.