Is it possible to prove that the pin code was valid at certain time?

[nipua]

Hello

I have secret key in my db, also I have exact time from logs, when method ValidateTwoFactorPIN was called. I need it for investigate some incidents, when users could give me information from their side about result of two factor validation. For example a pin '123456' and date '2022-06-06 14:34:51.797', could we check that this code was valid or invalid?

[ahwm]

@nipua since you closed this issue did you get it all figured out? I'm putting this here for benefit of anyone else with a similar use case.

There are some available overloads that would let you verify a PIN at a previous time.

var date = new DateTime(2022, 6, 6, 14, 34, 51, DateTimeKind.UTC);
var epoch = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.UTC);
var iteration = (long)(now - epoch).TotalSeconds / 30;
var pins = tfa.GetCurrentPins(secret, iteration);

// or
var isValid = tfa.ValidateTwoFactorPIN(secret, providedCodeFromClient, iteration);

[nipua]

@ahwm Yes, thanks a lot, your code is more elegant, I forked, and made a local nuget with simple method

[Fact]
public void ValidateTwoFactorPINBySpecificDate_ValidPIN_ReturnsTrue()
{
    string secretKey = "4d51cf64ec";
    DateTime specificDate = DateTime.Parse("6/10/2024 6:59:23");
    string pin = "678588";

    TwoFactorAuthenticator tfa = new TwoFactorAuthenticator();

    bool actual = tfa.ValidateTwoFactorPINBySpecificDate(secretKey, pin, specificDate);

    actual.ShouldBe(true);
}

public bool ValidateTwoFactorPINBySpecificDate(string accountSecretKey, string pin, DateTime specificDate, bool secretIsBase32 = false)
{
    var codes = new List<string>();
    var iterationCounter = GetCountersBySecificDate(specificDate);

    var iterationOffset = 0;

    if (DefaultClockDriftTolerance.TotalSeconds >= timeStep)
        iterationOffset = Convert.ToInt32(DefaultClockDriftTolerance.TotalSeconds / timeStep);

    var iterationStart = iterationCounter - iterationOffset;
    var iterationEnd = iterationCounter + iterationOffset;

    for (var counter = iterationStart; counter <= iterationEnd; counter++)
        codes.Add(GeneratePINAtInterval(accountSecretKey, counter));

    return codes.Contains(pin);
}

However, I understood that doesn't have matter, because the result of this method, all time will be equals with my logs, it's just for my superior.