1 files changed, 117 insertions, 0 deletions
diff --git a/TwoStepsAuthenticator.DotnetCore/TimeAuthenticator.cs b/TwoStepsAuthenticator.DotnetCore/TimeAuthenticator.cs
new file mode 100644
index 0000000..7272b77
--- /dev/null
+++ b/TwoStepsAuthenticator.DotnetCore/TimeAuthenticator.cs
@@ -0,0 +1,117 @@
+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;
+        }
+    }
+}