public static async Task <Step3Res> Do(
ServerDhParams.OkTag dhParams,
Int256 newNonce,
MtProtoPlainTransport transport
)
{
var key = Aes.GenerateKeyDataFromNonces(dhParams.ServerNonce.ToBytes(true), newNonce.ToBytes(true));
var plaintextAnswer = Aes.DecryptAES(key, dhParams.EncryptedAnswer.ToArrayUnsafe());
var dh = plaintextAnswer.Apply(Deserialize(WithHashSumCheck(ServerDhInnerData.Deserialize)));
Helpers.Assert(dh.Nonce == dhParams.Nonce, "auth step3: invalid nonce in encrypted answer");
Helpers.Assert(dh.ServerNonce == dhParams.ServerNonce, "auth step3: invalid server nonce in encrypted answer");
var currentEpochTime = Helpers.GetCurrentEpochTime();
var timeOffset = dh.ServerTime - currentEpochTime;
var g = dh.G;
var dhPrime = new BigInteger(1, dh.DhPrime.ToArrayUnsafe());
var ga = new BigInteger(1, dh.Ga.ToArrayUnsafe());
var b = new BigInteger(Rnd.NextBytes(2048));
var gb = BigInteger.ValueOf(g).ModPow(b, dhPrime);
var gab = ga.ModPow(b, dhPrime);
var dhInnerData = new ClientDhInnerData(
nonce: dh.Nonce,
serverNonce: dh.ServerNonce,
retryId: 0,
gb: gb.ToByteArrayUnsigned().ToBytesUnsafe()
);
var dhInnerDataBts = Serialize(dhInnerData);
var dhInnerDataHashedBts = WithHashAndPadding(dhInnerDataBts);
var dhInnerDataHashedEncryptedBytes = Aes.EncryptAES(key, dhInnerDataHashedBts);
var resp = await transport.Call(new SetClientDhParams(
nonce : dh.Nonce,
serverNonce : dh.ServerNonce,
encryptedData : dhInnerDataHashedEncryptedBytes.ToBytesUnsafe()
)).ConfigureAwait(false);
var res = resp.Match(
dhGenOkTag: x => x,
dhGenFailTag: _ => throw Helpers.FailedAssertion("auth step3: dh_gen_fail"),
dhGenRetryTag: _ => throw Helpers.FailedAssertion("auth step3: dh_gen_retry")
);
var authKey = AuthKey.FromGab(gab);
var newNonceHash = authKey.CalcNewNonceHash(newNonce.ToBytes(true), 1).ToInt128();
Helpers.Assert(res.Nonce == dh.Nonce, "auth step3: invalid nonce");
Helpers.Assert(res.ServerNonce == dh.ServerNonce, "auth step3: invalid server nonce");
Helpers.Assert(res.NewNonceHash1 == newNonceHash, "auth step3: invalid new nonce hash");
return(new Step3Res(authKey, timeOffset));
}
