Proper replacement for ed25519-java library

[davido]

As pointed out in str4d/ed25519-java#30, there are issue with export/import of ed25519 key:

// Bug in net.i2p.crypto.eddsa and in sshd? Both also compare the
            // seed of the private key, but for a generated key, this is some
            // random value, while it is all zeroes for a key read from a file.
            return KeyUtils.compareKeys(a.getPublic(), b.getPublic())
                    && Objects.equals(((EdDSAKey) a.getPrivate()).getParams(),
                            ((EdDSAKey) b.getPrivate()).getParams());

The answer was to examine ed25519-elisabeth library.

However, ed25519-elisabeth library lacks the necessary classes required to allows to use it as a SecurityProvider. Furthermore it's keys do not properly implement java.security.Private/PublicKey and/or java.security.Signature. Until it does, it cannot really be use as a replacement for ed25519-java.

Perhaps a more appropriate approach would be to examine and fix:

  Both also compare the seed of the private key,
  but for a generated key, this is some random value,
  while it is all zeroes for a key read from a file.