privateKeyToCurve25519 function
Implementation
List<int> privateKeyToCurve25519(Uint8List privateKey) {
final output = AccumulatorSink<Digest>();
sha512.startChunkedConversion(output)
..add(privateKey.sublist(0, 32))
..close();
final digest = output.events.single.bytes.sublist(0, 32);
digest[0] &= 248;
digest[31] &= 127;
digest[31] |= 64;
return digest;
}