// MD5 authentication provider.// Copyright (C) 2008-2010 Malcolm Crowe, Lex Li, and other contributors.// // Permission is hereby granted, free of charge, to any person obtaining a copy of this// software and associated documentation files (the "Software"), to deal in the Software// without restriction, including without limitation the rights to use, copy, modify, merge,// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons// to whom the Software is furnished to do so, subject to the following conditions:// // The above copyright notice and this permission notice shall be included in all copies or// substantial portions of the Software.// // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER// DEALINGS IN THE SOFTWARE.#if !NETFX_COREusing System;using System.Globalization;using System.IO;using System.Security.Cryptography; namespace GSF.Net.Snmp.Security{    /// <summary>    /// Authentication provider using MD5.    /// </summary>    public sealed class MD5AuthenticationProvider : IAuthenticationProvider    {        private const int Md5KeyCacheCapacity = 100;        private static readonly CryptoKeyCache Md5KeyCache = new CryptoKeyCache(Md5KeyCacheCapacity);        private static readonly object Md5KeyCacheLock = new object();         private readonly byte[] _password;         /// <summary>        /// Initializes a new instance of the <see cref="MD5AuthenticationProvider"/> class.        /// </summary>        /// <param name="phrase">The phrase.</param>        public MD5AuthenticationProvider(OctetString phrase)        {            if (phrase == null)            {                throw new ArgumentNullException(nameof(phrase));            }                        _password = phrase.GetRaw();        }                #region IAuthenticationProvider Members                 /// <summary>        /// Passwords to key.        /// </summary>        /// <param name="password">The user password.</param>        /// <param name="engineId">The engine ID.</param>        /// <returns></returns>        public byte[] PasswordToKey(byte[] password, byte[] engineId)        {            // key length has to be at least 8 bytes long (RFC3414)            if (password == null)            {                throw new ArgumentNullException(nameof(password));            }             if (engineId == null)            {                throw new ArgumentNullException(nameof(engineId));            }             if (password.Length < 8)            {                throw new ArgumentException($"Secret key is too short. Must be >= 8. Current: {password.Length}.", nameof(password));            }             lock (Md5KeyCacheLock)            {                byte[] cachedKey;                if (Md5KeyCache.TryGetCachedValue(password, engineId, out cachedKey))                {                    return cachedKey;                }                             byte[] keyToCache = _PasswordToKey(password, engineId);                 //Value not in cache compute and cache the value                Md5KeyCache.AddValueToCache(password, engineId, keyToCache);                return keyToCache;            }        }         private byte[] _PasswordToKey(byte[] password, byte[] engineId)        {                        using (MD5 md5 = MD5.Create())            {                int passwordIndex = 0;                int count = 0;                /* Use while loop until we've done 1 Megabyte */                byte[] sourceBuffer = new byte[1048576];                byte[] buf = new byte[64];                while (count < 1048576)                {                    for (int i = 0; i < 64; ++i)                    {                        // Take the next octet of the password, wrapping                        // to the beginning of the password as necessary.                        buf[i] = password[passwordIndex++ % password.Length];                    }                                        Buffer.BlockCopy(buf, 0, sourceBuffer, count, buf.Length);                    count += 64;                }                 byte[] digest = md5.ComputeHash(sourceBuffer);                 using (MemoryStream buffer = new MemoryStream())                {                    buffer.Write(digest, 0, digest.Length);                    buffer.Write(engineId, 0, engineId.Length);                    buffer.Write(digest, 0, digest.Length);                    return md5.ComputeHash(buffer.ToArray());                }            }        }         /// <summary>        /// Gets the clean digest.        /// </summary>        /// <value>The clean digest.</value>        public OctetString CleanDigest        {            get { return new OctetString(new byte[DigestLength]); }        }         /// <summary>        /// Computes the hash.        /// </summary>        /// <param name="version">The version.</param>        /// <param name="header">The header.</param>        /// <param name="parameters">The parameters.</param>        /// <param name="data">The scope data.</param>        /// <param name="privacy">The privacy provider.</param>        /// <param name="length">The length bytes.</param>        /// <returns></returns>        public OctetString ComputeHash(VersionCode version, ISegment header, SecurityParameters parameters, ISnmpData data, IPrivacyProvider privacy, byte[] length)        {            if (header == null)            {                throw new ArgumentNullException(nameof(header));            }                        if (parameters == null)            {                throw new ArgumentNullException(nameof(parameters));            }                        if (data == null)            {                throw new ArgumentNullException(nameof(data));            }                        if (privacy == null)            {                throw new ArgumentNullException(nameof(privacy));            }             byte[] key = PasswordToKey(_password, parameters.EngineId.GetRaw());            using (HMACMD5 md5 = new HMACMD5(key))            {                byte[] hash = md5.ComputeHash(ByteTool.PackMessage(length, version, header, parameters, data).ToBytes());#if NET471                md5.Clear();#endif                byte[] result = new byte[DigestLength];                Buffer.BlockCopy(hash, 0, result, 0, result.Length);                return new OctetString(result);            }        }         /// <summary>        /// Gets the length of the digest.        /// </summary>        /// <value>The length of the digest.</value>        public int DigestLength => 12;         #endregion         /// <summary>        /// Returns a <see cref="System.String"/> that represents this instance.        /// </summary>        /// <returns>        /// A <see cref="System.String"/> that represents this instance.        /// </returns>        public override string ToString()        {            return "MD5 authentication provider";        }    }}#endif