Update DARC expressions

[ineiti]

The following addition to DARC expressions would be very nice:

• lrs_ed25519(pub1, pub2, darc1, darc2, ...) resolves to true if a (Linkable) Ring Signature including these public-keys is received. Bonus-points if darcs can be given, too.

Discussing schnorr.Verify and the Scalar / Private key difference, the following darc-identity would be very nice to have:

• eddsa - this would enforce some security considerations on the private keys, as well as better verification and protection against some replay attacks (dedis/kyber#426)

[lhmerino]

+1, this would be very nice for e-voting as well.

[ineiti]

Hmm, I guess that for e-voting the current LRS will not work, as the size of the signature is 32 * group_size... Well, for EPFL it would be a 320kB signature. Not sure how long it would take to generate it, nor how long to verify it ;)