genSK function
Implementation
B64 genSK() {
var pair = x25519.generateKeyPair();
var sk = ed25519.newKeyFromSeed(Uint8List.fromList(pair.privateKey));
var list = List<int>.filled(32 + 32 + 32, 0);
list.setRange(0, 64, sk.bytes);
list.setRange(64, 64 + 32, pair.publicKey);
return B64.encode(list);
}