Change the pyelliptic dependency

[LefterisJP]

pyelliptic, a wrapper around OpenSSL that is used by this project should be replaced.

It does not work with OpenSSL version >= 1.1 and the maintainer stated that the project is dead.

In Raiden we use a fork of pyelliptic in order to be compatible with newer OpenSSL versions but that is just temporary.

The dependency should be changed and one suggestion would be pyOpenSSL

[ulope]

I don't know if it supports the required operations but generally cryptography is the go-to crypto library for python these days.

[ofek]

+1 for https://github.com/pyca/cryptography

[rbo727]

Just wanted to see if any work has been done on this? I require an OpenSSL version > 1.1 to get this to work on my system, but it doesn't appear that there is any support for that yet.

[Wolf480pl]

There's a pull request #81 attempting to fix this.

Not sure if people get notified if this issue is mentioned in a pull request, so I put this comment here just in case.