Can you please give a short code snippet that shows this behaviour? I think you're right that the public key should stay the same, but I'm not sure we're talking about the same public key...

I have added a test at the end of TestDKGResharing funtion in dkg_test.go to verify whether the old public key and the new public key are the same. I'm not sure if I'm doing it right. My app use this public key to encrypt messages and the threshold encryption/decryption works fine.

Here is the relevant code snippet from the test:

// 3. for i := 0; i < len(dkgs); i++ { require.Equal(t, shares[i].Public(), newShares[i].Public()) }

I'll have a look into it tomorrow, but it seems you're comparing the public keys of the different nodes, which of course will be different after resharing, because that's the point of it.

You might want to look if there is some Aggregate key or so and compare that, which should be the same before and after resharing.

And if you can create a PR with that additional test, it'll be easier for me to check it.

I reviewed the dkg code again, and what I should be checking is whether the public key of each node has changed before and after resharing. According to the code comments, the public polynomial should be different after resharing, but the first coefficient of the public polynomial (which is the dkg public key) should remain unchanged.

Can you test whether this one stays constant after resharing?

That's what I think must not change between resharing. Also, you could test that the following doesn't change, but this is already done in the tests:

https://github.com/dedis/kyber/blob/master/share/vss/pedersen/vss.go#L481

In a real-world implementation you should never have access to the other shares, so you will not be able to do the RecoverSecret. But you should always be able to do the func (d *DistKeyShare) Public() kyber.Point.

I hope that helps.

This is exactly what I am testing. In the test function, all the DistKeyShares generated by every node are stored in the 'shares' slice, and the DistKeyShares after resharing are stored in the 'newShares' slice. Therefore, I tested whether the Public is the same before and after resharing.

And the tests pass? So all is well now?

As far as I understand, this check is now present, it was introduced in #512 as we swapped our pedersen dkg implementation with the one from DRAND. Thank you for you work @leetingo ! I believe this issue as well as #491 can be closed.