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using System;
using System.Collections.Generic;
using System.Text;
using System.Security.Cryptography;
namespace OpenSim.Framework
{
/// <summary>
/// NEEDS AUDIT.
/// </summary>
/// <remarks>
/// Suggested implementation
/// <para>Store two digests for each foreign host. A local copy of the local hash using the local challenge (when issued), and a local copy of the remote hash using the remote challenge.</para>
/// <para>When sending data to the foreign host - run 'Sign' on the data and affix the returned byte[] to the message.</para>
/// <para>When recieving data from the foreign host - run 'Authenticate' against the data and the attached byte[].</para>
/// <para>Both hosts should be performing these operations for this to be effective.</para>
/// </remarks>
class RemoteDigest
{
private byte[] currentHash;
private byte[] secret;
private SHA512Managed SHA512;
/// <summary>
/// Initialises a new RemoteDigest authentication mechanism
/// </summary>
/// <remarks>Needs an audit by a cryptographic professional - was not "roll your own"'d by choice but rather a serious lack of decent authentication mechanisms in .NET remoting</remarks>
/// <param name="sharedSecret">The shared secret between systems (for inter-sim, this is provided in encrypted form during connection, for grid this is input manually in setup)</param>
/// <param name="salt">Binary salt - some common value - to be decided what</param>
/// <param name="challenge">The challenge key provided by the third party</param>
public RemoteDigest(string sharedSecret, byte[] salt, string challenge)
{
SHA512 = new SHA512Managed();
Rfc2898DeriveBytes RFC2898 = new Rfc2898DeriveBytes(sharedSecret,salt);
secret = RFC2898.GetBytes(512);
ASCIIEncoding ASCII = new ASCIIEncoding();
currentHash = SHA512.ComputeHash(AppendArrays(secret, ASCII.GetBytes(challenge)));
}
/// <summary>
/// Authenticates a piece of incoming data against the local digest. Upon successful authentication, digest string is incremented.
/// </summary>
/// <param name="data">The incoming data</param>
/// <param name="digest">The remote digest</param>
/// <returns></returns>
public bool Authenticate(byte[] data, byte[] digest)
{
byte[] newHash = SHA512.ComputeHash(AppendArrays(AppendArrays(currentHash, secret), data));
if (digest == newHash)
{
currentHash = newHash;
return true;
}
else
{
throw new Exception("Hash comparison failed. Key resync required.");
}
}
/// <summary>
/// Signs a new bit of data with the current hash. Returns a byte array which should be affixed to the message.
/// Signing a piece of data will automatically increment the hash - if you sign data and do not send it, the
/// hashes will get out of sync and throw an exception when validation is attempted.
/// </summary>
/// <param name="data">The outgoing data</param>
/// <returns>The local digest</returns>
public byte[] Sign(byte[] data)
{
currentHash = SHA512.ComputeHash(AppendArrays(AppendArrays(currentHash, secret), data));
return currentHash;
}
/// <summary>
/// Generates a new challenge string to be issued to a foreign host. Challenges are 1024-bit (effective strength of less than 512-bits) messages generated using the Crytographic Random Number Generator.
/// </summary>
/// <returns>A 128-character hexadecimal string containing the challenge.</returns>
public static string GenerateChallenge()
{
RNGCryptoServiceProvider RNG = new RNGCryptoServiceProvider();
byte[] bytes = new byte[64];
RNG.GetBytes(bytes);
StringBuilder sb = new StringBuilder(bytes.Length * 2);
foreach (byte b in bytes)
{
sb.AppendFormat("{0:x2}", b);
}
return sb.ToString();
}
/// <summary>
/// Helper function, merges two byte arrays
/// </summary>
/// <remarks>Sourced from MSDN Forum</remarks>
/// <param name="a">A</param>
/// <param name="b">B</param>
/// <returns>C</returns>
private byte[] AppendArrays(byte[] a, byte[] b)
{
byte[] c = new byte[a.Length + b.Length];
Buffer.BlockCopy(a, 0, c, 0, a.Length);
Buffer.BlockCopy(b, 0, c, a.Length, b.Length);
return c;
}
}
}
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