/* * Copyright (c) Contributors, http://opensimulator.org/ * See CONTRIBUTORS.TXT for a full list of copyright holders. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions are met: * * Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * * Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * Neither the name of the OpenSim Project nor the * names of its contributors may be used to endorse or promote products * derived from this software without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE * DISCLAIMED. IN NO EVENT SHALL THE CONTRIBUTORS BE LIABLE FOR ANY * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */ using System; using System.Security.Cryptography; using System.Text; 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 receiving 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> internal 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 static 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; } } }