/// <summary>
/// Constructs an instance by parsing a serialized string.
/// </summary>
/// <param name="serialized">The serialized visitor information.</param>
/// <exception cref="ArgumentNullException">Thrown if <c>null</c> is passed.</exception>
/// <exception cref="ArgumentException">Thrown if the parameter passed does not represent a valid <see cref="UniqueVisitor" /> instance.</exception>
/// <remarks>
/// <para>
/// The <paramref name="serialized" /> value must have been generated by
/// a previous call to <see cref="ToString" />.
/// </para>
/// </remarks>
public UniqueVisitor(string serialized)
{
if (serialized == null)
{
throw new ArgumentNullException("serialized");
}
try
{
using (var ms = new EnhancedMemoryStream(Convert.FromBase64String(serialized)))
{
if (ms.ReadInt16() != Magic)
{
throw new FormatException("Bad magic number.");
}
this.IssueDateUtc = new DateTime(ms.ReadInt64(), DateTimeKind.Utc);
this.ID = new Guid(ms.ReadBytes(32));
}
}
catch (Exception e)
{
throw new ArgumentException("Invalid unique serialized visitor.", "seralized", e);
}
}
public void EnhancedMemoryStream_ReadWriteBytesNoLen()
{
var es = new EnhancedMemoryStream();
es.WriteBytesNoLen(new byte[] { 0, 1, 2, 3 });
es.Seek(0, SeekOrigin.Begin);
CollectionAssert.AreEqual(new byte[] { 0, 1, 2, 3 }, es.ReadBytes(4));
}
/// <summary>
/// Verifies request arguments against a signature using a shared <see cref="SymmetricKey" />
/// and the current time.
/// </summary>
/// <param name="sharedKey">The shared <see cref="SymmetricKey" />.</param>
/// <param name="signature">The base-64 encoded signature.</param>
/// <param name="args">The request argument collection.</param>
/// <param name="signatureKey">
/// The name of the signature key within the event arguments or <c>null</c>
/// if the signature is not present.
/// </param>
/// <param name="graceInterval">Specifies the time period used for verifying the signature request time.</param>
/// <returns><c>true</c> if the signature is valid.</returns>
/// <remarks>
/// <para>
/// <paramref name="graceInterval" /> is used when comparing the request time (UTC) embedded
/// in the signature with the current machine time (UTC). Request times within the range of:
/// </para>
/// <code language="none">
/// DateTime.UtcNow - graceInterval <= requestTime <= DateTime.UtcNow + graceInterval
/// </code>
/// <para>
/// will be considered to be valid. Request times outside this range will be invalid.
/// Larger grace intervals provide help avoid the problems of incorrect system times or
/// long request delivery delays but at the price of the increased exposure to replay
/// attacks.
/// </para>
/// <note>
/// If the signature is present in the arguments, then the <paramref name="signatureKey" /> <b>must</b>
/// be passed as its name or else the verification will always fail. The reason for this is
/// that the hash was originally computed before the signature was added so the hash will be
/// different if it includes the signature.
/// </note>
/// </remarks>
public static bool TryVerify(SymmetricKey sharedKey, string signature, ArgCollection args, string signatureKey, TimeSpan graceInterval)
{
try
{
byte[] encrypted = Convert.FromBase64String(signature);
byte[] decrypted;
byte[] requestHash;
byte[] hash;
DateTime requestTime;
DateTime now;
decrypted = Crypto.Decrypt(encrypted, sharedKey);
if (decrypted.Length != Size)
{
return(false);
}
using (var ms = new EnhancedMemoryStream(decrypted))
{
ms.Position = 8;
if (ms.ReadInt32() != Magic)
{
return(false);
}
requestTime = new DateTime(ms.ReadInt64());
requestHash = ms.ReadBytes(SHA1Hasher.DigestSize);
}
now = DateTime.UtcNow;
if (!Helper.Within(requestTime, now, graceInterval))
{
return(false);
}
hash = ComputeHash(args, signatureKey);
return(Helper.ArrayEquals(requestHash, hash));
}
catch
{
return(false);
}
}
/// <summary>
/// Decrypts and deserializes a message from a byte buffer.
/// </summary>
/// <param name="buffer">The buffer.</param>
/// <param name="sharedKey">The shared encryption key.</param>
/// <exception cref="FormatException">Thrown if the buffer does not contain a valid message.</exception>
public UdpBroadcastMessage(byte[] buffer, SymmetricKey sharedKey)
{
try
{
using (var ms = new EnhancedMemoryStream(Crypto.Decrypt(buffer, sharedKey)))
{
if (ms.ReadInt32Le() != Magic)
{
throw new Exception();
}
this.TimeStampUtc = new DateTime(ms.ReadInt64Le());
this.SourceAddress = new IPAddress(ms.ReadBytes(4));
this.MessageType = (UdpBroadcastMessageType)ms.ReadByte();
this.BroadcastGroup = ms.ReadByte();
this.Payload = ms.ReadBytes16();
}
}
catch (Exception e)
{
throw new FormatException("Invalid UDP broadcast message.", e);
}
}