Convert Ed25519PrivateKeyParameters to X25519PrivateKeyParameters about bc-csharp

[nd1012]

I don't get it.

However, after looking into the internal Bouncy Castle Ed25519 and X25519 private key generation methods for the differences between the key formats, it seemed to be actually simple. So I wrote a little extension method that does the conversion:

public static X25519PrivateKeyParameters ToX25519PrivateKey(this Ed25519PrivateKeyParameters key)
{
	byte[] data = key.GetEncoded();
	data[0] &= 248;
	data[31] &= 127;
	data[31] |= 64;
	return new(data);
}

In my tests it worked well. Anyway, it can cause collisions (getting the same X25519 key from different Ed25519 keys).

[cipherboy]

@nd1012 This conversion looks good to me and matches what is present elsewhere as well.

[Richiedevop]

Ed25519PrivateKeyParameters

[Richiedevop]

X25519PrivateKeyParameters

[nd1012]

Thanks for your feedback, that makes me feel more confident :)