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using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace TwoStepsAuthenticator
{
/// <summary>
/// Implementation of rfc6238 Time-Based One-Time Password Algorithm
/// </summary>
public class TimeAuthenticator : Authenticator
{
private static readonly Lazy<IUsedCodesManager> DefaultUsedCodeManager = new Lazy<IUsedCodesManager>(() => new UsedCodesManager());
private readonly Func<DateTime> NowFunc;
private readonly IUsedCodesManager UsedCodeManager;
private readonly int IntervalSeconds;
public TimeAuthenticator(IUsedCodesManager usedCodeManager = null, Func<DateTime> nowFunc = null, int intervalSeconds = 30)
{
this.NowFunc = (nowFunc == null) ? () => DateTime.Now : nowFunc;
this.UsedCodeManager = (usedCodeManager == null) ? DefaultUsedCodeManager.Value : usedCodeManager;
this.IntervalSeconds = intervalSeconds;
}
/// <summary>
/// Generates One-Time Password.
/// </summary>
/// <param name="secret">Shared Secret</param>
/// <returns>OTP</returns>
public string GetCode(string secret)
{
return GetCode(secret, NowFunc());
}
/// <summary>
/// Generates One-Time Password.
/// </summary>
/// <param name="secret">Shared Secret</param>
/// <param name="date">Time to use as challenge</param>
/// <returns>OTP</returns>
public string GetCode(string secret, DateTime date)
{
return GetCodeInternal(secret, (ulong)GetInterval(date));
}
/// <summary>
/// Checks if the passed code is valid.
/// </summary>
/// <param name="secret">Shared Secret</param>
/// <param name="code">OTP</param>
/// <param name="user">The user</param>
/// <returns>true if code matches</returns>
public bool CheckCode(string secret, string code, object user)
{
DateTime successfulTime = DateTime.MinValue;
return CheckCode(secret, code, user, out successfulTime);
}
/// <summary>
/// Checks if the passed code is valid.
/// </summary>
/// <param name="secret">Shared Secret</param>
/// <param name="code">OTP</param>
/// <param name="user">The user</param>
/// <param name="usedDateTime">Matching time if successful</param>
/// <returns>true if code matches</returns>
public bool CheckCode(string secret, string code, object user, out DateTime usedDateTime)
{
var baseTime = NowFunc();
DateTime successfulTime = DateTime.MinValue;
// We need to do this in constant time
var codeMatch = false;
for (int i = -2; i <= 1; i++)
{
var checkTime = baseTime.AddSeconds(IntervalSeconds * i);
var checkInterval = GetInterval(checkTime);
if (ConstantTimeEquals(GetCode(secret, checkTime), code) && (user == null || !UsedCodeManager.IsCodeUsed(checkInterval, code, user)))
{
codeMatch = true;
successfulTime = checkTime;
UsedCodeManager.AddCode(checkInterval, code, user);
}
}
usedDateTime = successfulTime;
return codeMatch;
}
/// <summary>
/// Checks if the passed code is valid.
/// </summary>
/// <param name="secret">Shared Secret</param>
/// <param name="code">OTP</param>
/// <returns>true if code matches</returns>
[Obsolete("The CheckCode method should only be used with a user object")]
public bool CheckCode(string secret, string code)
{
DateTime successfulTime = DateTime.MinValue;
return CheckCode(secret, code, null, out successfulTime);
}
private long GetInterval(DateTime dateTime)
{
TimeSpan ts = (dateTime.ToUniversalTime() - new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc));
return (long)ts.TotalSeconds / IntervalSeconds;
}
}
}
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