1 files changed, 148 insertions, 0 deletions
diff --git a/src/DotNetOpenAuth.Messaging/Messaging/Bindings/StandardReplayProtectionBindingElement.cs b/src/DotNetOpenAuth.Messaging/Messaging/Bindings/StandardReplayProtectionBindingElement.cs
new file mode 100644
index 0000000..bb56cfd
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+++ b/src/DotNetOpenAuth.Messaging/Messaging/Bindings/StandardReplayProtectionBindingElement.cs
@@ -0,0 +1,148 @@
+//-----------------------------------------------------------------------
+// <copyright file="StandardReplayProtectionBindingElement.cs" company="Andrew Arnott">
+//     Copyright (c) Andrew Arnott. All rights reserved.
+// </copyright>
+//-----------------------------------------------------------------------
+
+namespace DotNetOpenAuth.Messaging.Bindings {
+	using System;
+	using System.Diagnostics;
+	using System.Diagnostics.Contracts;
+
+	/// <summary>
+	/// A binding element that checks/verifies a nonce message part.
+	/// </summary>
+	internal class StandardReplayProtectionBindingElement : IChannelBindingElement {
+		/// <summary>
+		/// These are the characters that may be chosen from when forming a random nonce.
+		/// </summary>
+		private const string AllowedCharacters = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
+
+		/// <summary>
+		/// The persistent store for nonces received.
+		/// </summary>
+		private INonceStore nonceStore;
+
+		/// <summary>
+		/// The length of generated nonces.
+		/// </summary>
+		private int nonceLength = 8;
+
+		/// <summary>
+		/// Initializes a new instance of the <see cref="StandardReplayProtectionBindingElement"/> class.
+		/// </summary>
+		/// <param name="nonceStore">The store where nonces will be persisted and checked.</param>
+		internal StandardReplayProtectionBindingElement(INonceStore nonceStore)
+			: this(nonceStore, false) {
+		}
+
+		/// <summary>
+		/// Initializes a new instance of the <see cref="StandardReplayProtectionBindingElement"/> class.
+		/// </summary>
+		/// <param name="nonceStore">The store where nonces will be persisted and checked.</param>
+		/// <param name="allowEmptyNonces">A value indicating whether zero-length nonces will be allowed.</param>
+		internal StandardReplayProtectionBindingElement(INonceStore nonceStore, bool allowEmptyNonces) {
+			Contract.Requires<ArgumentNullException>(nonceStore != null);
+
+			this.nonceStore = nonceStore;
+			this.AllowZeroLengthNonce = allowEmptyNonces;
+		}
+
+		#region IChannelBindingElement Properties
+
+		/// <summary>
+		/// Gets the protection that this binding element provides messages.
+		/// </summary>
+		public MessageProtections Protection {
+			get { return MessageProtections.ReplayProtection; }
+		}
+
+		/// <summary>
+		/// Gets or sets the channel that this binding element belongs to.
+		/// </summary>
+		public Channel Channel { get; set; }
+
+		#endregion
+
+		/// <summary>
+		/// Gets or sets the strength of the nonce, which is measured by the number of
+		/// nonces that could theoretically be generated.
+		/// </summary>
+		/// <remarks>
+		/// The strength of the nonce is equal to the number of characters that might appear
+		/// in the nonce to the power of the length of the nonce.
+		/// </remarks>
+		internal double NonceStrength {
+			get {
+				return Math.Pow(AllowedCharacters.Length, this.nonceLength);
+			}
+
+			set {
+				value = Math.Max(value, AllowedCharacters.Length);
+				this.nonceLength = (int)Math.Log(value, AllowedCharacters.Length);
+				Debug.Assert(this.nonceLength > 0, "Nonce length calculated to be below 1!");
+			}
+		}
+
+		/// <summary>
+		/// Gets or sets a value indicating whether empty nonces are allowed.
+		/// </summary>
+		/// <value>Default is <c>false</c>.</value>
+		internal bool AllowZeroLengthNonce { get; set; }
+
+		#region IChannelBindingElement Methods
+
+		/// <summary>
+		/// Applies a nonce to the message.
+		/// </summary>
+		/// <param name="message">The message to apply replay protection to.</param>
+		/// <returns>
+		/// The protections (if any) that this binding element applied to the message.
+		/// Null if this binding element did not even apply to this binding element.
+		/// </returns>
+		public MessageProtections? ProcessOutgoingMessage(IProtocolMessage message) {
+			IReplayProtectedProtocolMessage nonceMessage = message as IReplayProtectedProtocolMessage;
+			if (nonceMessage != null) {
+				nonceMessage.Nonce = this.GenerateUniqueFragment();
+				return MessageProtections.ReplayProtection;
+			}
+
+			return null;
+		}
+
+		/// <summary>
+		/// Verifies that the nonce in an incoming message has not been seen before.
+		/// </summary>
+		/// <param name="message">The incoming message.</param>
+		/// <returns>
+		/// The protections (if any) that this binding element applied to the message.
+		/// Null if this binding element did not even apply to this binding element.
+		/// </returns>
+		/// <exception cref="ReplayedMessageException">Thrown when the nonce check revealed a replayed message.</exception>
+		public MessageProtections? ProcessIncomingMessage(IProtocolMessage message) {
+			IReplayProtectedProtocolMessage nonceMessage = message as IReplayProtectedProtocolMessage;
+			if (nonceMessage != null && nonceMessage.Nonce != null) {
+				ErrorUtilities.VerifyProtocol(nonceMessage.Nonce.Length > 0 || this.AllowZeroLengthNonce, MessagingStrings.InvalidNonceReceived);
+
+				if (!this.nonceStore.StoreNonce(nonceMessage.NonceContext, nonceMessage.Nonce, nonceMessage.UtcCreationDate)) {
+					Logger.OpenId.ErrorFormat("Replayed nonce detected ({0} {1}).  Rejecting message.", nonceMessage.Nonce, nonceMessage.UtcCreationDate);
+					throw new ReplayedMessageException(message);
+				}
+
+				return MessageProtections.ReplayProtection;
+			}
+
+			return null;
+		}
+
+		#endregion
+
+		/// <summary>
+		/// Generates a string of random characters for use as a nonce.
+		/// </summary>
+		/// <returns>The nonce string.</returns>
+		private string GenerateUniqueFragment() {
+			return MessagingUtilities.GetRandomString(this.nonceLength, AllowedCharacters);
+		}
+	}
+}