This expands on Dodgyrabbit's answer and his code helped to fix mine as I developed this. This generic class can use any HMAC-derived class in C#. This is .NET 4 because of the parameters with default values, but if those were changed then this should work down to .NET 2, but I haven't tested that. USE AT YOUR OWN RISK.
I have also posted this on my blog, The Albequerque Left Turn, today.
using System; using System.Text; using System.Security.Cryptography; namespace System.Security.Cryptography { //Generic PBKDF2 Class that can use any HMAC algorithm derived from the // System.Security.Cryptography.HMAC abstract class // PER SPEC RFC2898 with help from user Dodgyrabbit on StackExchange // http://stackoverflow.com/questions/1046599/pbkdf2-implementation-in-c-sharp-with-rfc2898derivebytes // the use of default values for parameters in the functions puts this at .NET 4 // if you remove those defaults and create the required constructors, you should be able to drop to .NET 2 // USE AT YOUR OWN RISK! I HAVE TESTED THIS AGAINST PUBLIC TEST VECTORS, BUT YOU SHOULD // HAVE YOUR CODE PEER-REVIEWED AND SHOULD FOLLOW BEST PRACTICES WHEN USING CRYPTO-ANYTHING! // NO WARRANTY IMPLIED OR EXPRESSED, YOU ARE ON YOUR OWN! // PUBLIC DOMAIN! NO COPYRIGHT INTENDED OR RESERVED! //constrain T to be any class that derives from HMAC, and that exposes a new() constructor public class PBKDF2<T>: DeriveBytes where T : HMAC, new() { //Internal variables and public properties private int _blockSize = -1; // the byte width of the output of the HMAC algorithm byte[] _P = null; int _C = 0; private T _hmac; byte[] _S = null; // if you called the initializer/constructor specifying a salt size, // you will need this property to GET the salt after it was created from the crypto rng! // GET THIS BEFORE CALLING GETBYTES()! OBJECT WILL BE RESET AFTER GETBYTES() AND // SALT WILL BE LOST!! public byte[] Salt { get { return (byte[])_S.Clone(); } } // Constructors public PBKDF2(string Password, byte[] Salt, int IterationCount = 1000) { Initialize(Password, Salt, IterationCount); } public PBKDF2(byte[] Password, byte[] Salt, int IterationCount = 1000) { Initialize(Password, Salt, IterationCount); } public PBKDF2(string Password, int SizeOfSaltInBytes, int IterationCount = 1000) { Initialize(Password, SizeOfSaltInBytes, IterationCount);} public PBKDF2(byte[] Password, int SizeOfSaltInBytes, int IterationCount = 1000) { Initialize(Password, SizeOfSaltInBytes, IterationCount);} //All Construtors call the corresponding Initialize methods public void Initialize(string Password, byte[] Salt, int IterationCount = 1000) { if (string.IsNullOrWhiteSpace(Password)) throw new ArgumentException("Password must contain meaningful characters and not be null.", "Password"); if (IterationCount < 1) throw new ArgumentOutOfRangeException("IterationCount"); Initialize(new UTF8Encoding(false).GetBytes(Password), Salt, IterationCount); } public void Initialize(byte[] Password, byte[] Salt, int IterationCount = 1000) { //all Constructors/Initializers eventually lead to this one which does all the "important" work if (Password == null || Password.Length == 0) throw new ArgumentException("Password cannot be null or empty.", "Password"); if (Salt == null) Salt = new byte[0]; if (IterationCount < 1) throw new ArgumentOutOfRangeException("IterationCount"); _P = (byte[])Password.Clone(); _S = (byte[])Salt.Clone(); _C = IterationCount; //determine _blockSize _hmac = new T(); _hmac.Key = new byte[] { 0 }; byte[] test = _hmac.ComputeHash(new byte[] { 0 }); _blockSize = test.Length; } public void Initialize(string Password, int SizeOfSaltInBytes, int IterationCount = 1000) { if (string.IsNullOrWhiteSpace(Password)) throw new ArgumentException("Password must contain meaningful characters and not be null.", "Password"); if (IterationCount < 1) throw new ArgumentOutOfRangeException("IterationCount"); Initialize(new UTF8Encoding(false).GetBytes(Password), SizeOfSaltInBytes, IterationCount); } public void Initialize(byte[] Password, int SizeOfSaltInBytes, int IterationCount = 1000) { if (Password == null || Password.Length == 0) throw new ArgumentException("Password cannot be null or empty.", "Password"); if (SizeOfSaltInBytes < 0) throw new ArgumentOutOfRangeException("SizeOfSaltInBytes"); if (IterationCount < 1) throw new ArgumentOutOfRangeException("IterationCount"); // You didn't specify a salt, so I'm going to create one for you of the specific byte length byte[] data = new byte[SizeOfSaltInBytes]; RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider(); rng.GetBytes(data); // and then finish initializing... // Get the salt from the Salt parameter BEFORE calling GetBytes()!!!!!!!!!!! Initialize(Password, data, IterationCount); } ~PBKDF2() { //*DOOT* clean up in aisle 5! *KEKERKCRACKLE* this.Reset(); } // required by the Derive Bytes class/interface // this is where you request your output bytes after Initialize // state of class Reset after use! public override byte[] GetBytes(int ByteCount) { if (_S == null || _P == null) throw new InvalidOperationException("Object not Initialized!"); if (ByteCount < 1)// || ByteCount > uint.MaxValue * blockSize) throw new ArgumentOutOfRangeException("ByteCount"); int totalBlocks = (int)Math.Ceiling((decimal)ByteCount / _blockSize); int partialBlock = (int)(ByteCount % _blockSize); byte[] result = new byte[ByteCount]; byte[] buffer = null; // I'm using TT here instead of T from the spec because I don't want to confuse it with // the generic object T for (int TT = 1; TT <= totalBlocks; TT++) { // run the F function with the _C number of iterations for block number TT buffer = _F((uint)TT); //IF we're not at the last block requested //OR the last block requested is whole (not partial) // then take everything from the result of F for this block number TT //ELSE only take the needed bytes from F if (TT != totalBlocks || (TT == totalBlocks && partialBlock == 0)) Buffer.BlockCopy(buffer, 0, result, _blockSize * (TT - 1), _blockSize); else Buffer.BlockCopy(buffer, 0, result, _blockSize * (TT - 1), partialBlock); } this.Reset(); // force cleanup after every use! Cannot be reused! return result; } // required by the Derive Bytes class/interface public override void Reset() { _C = 0; _P.Initialize(); // the compiler might optimize this line out! :( _P = null; _S.Initialize(); // the compiler might optimize this line out! :( _S = null; if (_hmac != null) _hmac.Clear(); _blockSize = -1; } // the core function of the PBKDF which does all the iterations // per the spec section 5.2 step 3 private byte[] _F(uint I) { //NOTE: SPEC IS MISLEADING!!! //THE HMAC FUNCTIONS ARE KEYED BY THE PASSWORD! NEVER THE SALT! byte[] bufferU = null; byte[] bufferOut = null; byte[] _int = PBKDF2<T>.IntToBytes(I); _hmac = new T(); _hmac.Key = (_P); // KEY BY THE PASSWORD! _hmac.TransformBlock(_S, 0, _S.Length, _S, 0); _hmac.TransformFinalBlock(_int, 0, _int.Length); bufferU = _hmac.Hash; bufferOut = (byte[])bufferU.Clone(); for (int c = 1; c < _C; c++) { _hmac.Initialize(); _hmac.Key = _P; // KEY BY THE PASSWORD! bufferU = _hmac.ComputeHash(bufferU); _Xor(ref bufferOut, bufferU); } return bufferOut; } // XOR one array of bytes into another (which is passed by reference) // this is the equiv of data ^= newData; private void _Xor(ref byte[] data, byte[] newData) { for (int i = data.GetLowerBound(0); i <= data.GetUpperBound(0); i++) data[i] ^= newData[i]; } // convert an unsigned int into an array of bytes BIG ENDIEN // per the spec section 5.2 step 3 static internal byte[] IntToBytes(uint i) { byte[] bytes = BitConverter.GetBytes(i); if (!BitConverter.IsLittleEndian) { return bytes; } else { Array.Reverse(bytes); return bytes; } } } }
