Rfc2898DeriveBytes.cs source code in C# .NET

                        Code:
                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / clr / src / BCL / System / Security / Cryptography / Rfc2898DeriveBytes.cs / 1305376 / Rfc2898DeriveBytes.cs
                        
                        
                            // ==++== 
//
//   Copyright (c) Microsoft Corporation.  All rights reserved.
//
// ==--== 
// [....]
// 
 
//
// Rfc2898DeriveBytes.cs 
//

// This implementation follows RFC 2898 recommendations. See http://www.ietf.org/rfc/Rfc2898.txt
// It uses HMACSHA1 as the underlying pseudorandom function. 

namespace System.Security.Cryptography { 
    using System.Globalization; 
    using System.IO;
    using System.Text; 
    using System.Diagnostics.Contracts;

    [System.Runtime.InteropServices.ComVisible(true)]
    public class Rfc2898DeriveBytes : DeriveBytes 
    {
        private byte[] m_buffer; 
        private byte[] m_salt; 
        private HMACSHA1 m_hmacsha1;  // The pseudo-random generator function used in PBKDF2
 
        private uint m_iterations;
        private uint m_block;
        private int m_startIndex;
        private int m_endIndex; 

        private const int BlockSize = 20; 
 
        //
        // public constructors 
        //

        public Rfc2898DeriveBytes(string password, int saltSize) : this(password, saltSize, 1000) {}
 
        public Rfc2898DeriveBytes(string password, int saltSize, int iterations) {
            if (saltSize < 0) 
                throw new ArgumentOutOfRangeException("saltSize", Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum")); 
            Contract.EndContractBlock();
 
            byte[] salt = new byte[saltSize];
            Utils.StaticRandomNumberGenerator.GetBytes(salt);

            Salt = salt; 
            IterationCount = iterations;
            m_hmacsha1 = new HMACSHA1(new UTF8Encoding(false).GetBytes(password)); 
            Initialize(); 
        }
 
        public Rfc2898DeriveBytes(string password, byte[] salt) : this(password, salt, 1000) {}

        public Rfc2898DeriveBytes(string password, byte[] salt, int iterations) : this (new UTF8Encoding(false).GetBytes(password), salt, iterations) {}
 
        public Rfc2898DeriveBytes(byte[] password, byte[] salt, int iterations) {
            Salt = salt; 
            IterationCount = iterations; 
            m_hmacsha1 = new HMACSHA1(password);
            Initialize(); 
        }

        //
        // public properties 
        //
 
        public int IterationCount { 
            get { return (int) m_iterations; }
            set { 
                if (value <= 0)
                    throw new ArgumentOutOfRangeException("value", Environment.GetResourceString("ArgumentOutOfRange_NeedPosNum"));
                Contract.EndContractBlock();
                m_iterations = (uint) value; 
                Initialize();
            } 
        } 

        public byte[] Salt { 
            get { return (byte[]) m_salt.Clone(); }
            set {
                if (value == null)
                    throw new ArgumentNullException("value"); 
                if (value.Length < 8)
                    throw new ArgumentException(Environment.GetResourceString("Cryptography_PasswordDerivedBytes_FewBytesSalt")); 
                Contract.EndContractBlock(); 
                m_salt = (byte[]) value.Clone();
                Initialize(); 
            }
        }

        // 
        // public methods
        // 
 
        [System.Security.SecuritySafeCritical]  // auto-generated
        public override byte[] GetBytes(int cb) { 
            if (cb <= 0)
                throw new ArgumentOutOfRangeException("cb", Environment.GetResourceString("ArgumentOutOfRange_NeedPosNum"));
            Contract.EndContractBlock();
            byte[] password = new byte[cb]; 

            int offset = 0; 
            int size = m_endIndex - m_startIndex; 
            if (size > 0) {
                if (cb >= size) { 
                    Buffer.InternalBlockCopy(m_buffer, m_startIndex, password, 0, size);
                    m_startIndex = m_endIndex = 0;
                    offset += size;
                } else { 
                    Buffer.InternalBlockCopy(m_buffer, m_startIndex, password, 0, cb);
                    m_startIndex += cb; 
                    return password; 
                }
            } 

            Contract.Assert(m_startIndex == 0 && m_endIndex == 0, "Invalid start or end index in the internal buffer." );

            while(offset < cb) { 
                byte[] T_block = Func();
                int remainder = cb - offset; 
                if(remainder > BlockSize) { 
                    Buffer.InternalBlockCopy(T_block, 0, password, offset, BlockSize);
                    offset += BlockSize; 
                } else {
                    Buffer.InternalBlockCopy(T_block, 0, password, offset, remainder);
                    offset += remainder;
                    Buffer.InternalBlockCopy(T_block, remainder, m_buffer, m_startIndex, BlockSize - remainder); 
                    m_endIndex += (BlockSize - remainder);
                    return password; 
                } 
            }
            return password; 
        }

        public override void Reset() {
            Initialize(); 
        }
 
        protected override void Dispose(bool disposing) { 
            base.Dispose(disposing);
 
            if (disposing) {
                if (m_hmacsha1 != null) {
                    ((IDisposable)m_hmacsha1).Dispose();
                } 

                if (m_buffer != null) { 
                    Array.Clear(m_buffer, 0, m_buffer.Length); 
                }
                if (m_salt != null) { 
                    Array.Clear(m_salt, 0, m_salt.Length);
                }
            }
        } 

        private void Initialize() { 
            if (m_buffer != null) 
                Array.Clear(m_buffer, 0, m_buffer.Length);
            m_buffer = new byte[BlockSize]; 
            m_block = 1;
            m_startIndex = m_endIndex = 0;
        }
 
        // This function is defined as follow :
        // Func (S, i) = HMAC(S || i) | HMAC2(S || i) | ... | HMAC(iterations) (S || i) 
        // where i is the block number. 
        private byte[] Func () {
            byte[] INT_block = Utils.Int(m_block); 

            m_hmacsha1.TransformBlock(m_salt, 0, m_salt.Length, m_salt, 0);
            m_hmacsha1.TransformFinalBlock(INT_block, 0, INT_block.Length);
            byte[] temp = m_hmacsha1.Hash; 
            m_hmacsha1.Initialize();
 
            byte[] ret = temp; 
            for (int i = 2; i <= m_iterations; i++) {
                temp = m_hmacsha1.ComputeHash(temp); 
                for (int j = 0; j < BlockSize; j++) {
                    ret[j] ^= temp[j];
                }
            } 

            // increment the block count. 
            m_block++; 
            return ret;
        } 
    }
}

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
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Rfc2898DeriveBytes.cs source code in C# .NET

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