//Copyright (c) 2012 Josip Medved <jmedved@jmedved.com>

//2012-04-12: Initial version.

using System;

using System.Security.Cryptography;

using System.Text;

namespace PBKDF2 {

/// <summary>

/// Generic PBKDF2 implementation.

/// </summary>

/// <example>This sample shows how to initialize class with SHA-256 HMAC.

/// <code>

/// using (var hmac = new HMACSHA256()) {

/// var df = new Pbkdf2(hmac, "password", "salt");

/// var bytes = df.GetBytes();

/// }

/// </code>

/// </example>

[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Naming", "CA1704:IdentifiersShouldBeSpelledCorrectly", MessageId = "Pbkdf", Justification = "Spelling is correct.")]

public class Pbkdf2 {

/// <summary>

/// Creates new instance.

/// </summary>

/// <param name="algorithm">HMAC algorithm to use.</param>

/// <param name="password">The password used to derive the key.</param>

/// <param name="salt">The key salt used to derive the key.</param>

/// <param name="iterations">The number of iterations for the operation.</param>

/// <exception cref="System.ArgumentNullException">Algorithm cannot be null - Password cannot be null. -or- Salt cannot be null.</exception>

public Pbkdf2(HMAC algorithm, Byte[] password, Byte[] salt, Int32 iterations) {

if (algorithm == null) { throw new ArgumentNullException("algorithm", "Algorithm cannot be null."); }

if (salt == null) { throw new ArgumentNullException("salt", "Salt cannot be null."); }

if (password == null) { throw new ArgumentNullException("password", "Password cannot be null."); }

this.Algorithm = algorithm;

this.Algorithm.Key = password;

this.Salt = salt;

this.IterationCount = iterations;

this.BlockSize = this.Algorithm.HashSize / 8;

this.BufferBytes = new byte[this.BlockSize];

}

/// <summary>

/// Creates new instance.

/// </summary>

/// <param name="algorithm">HMAC algorithm to use.</param>

/// <param name="password">The password used to derive the key.</param>

/// <param name="salt">The key salt used to derive the key.</param>

/// <exception cref="System.ArgumentNullException">Algorithm cannot be null - Password cannot be null. -or- Salt cannot be null.</exception>

public Pbkdf2(HMAC algorithm, Byte[] password, Byte[] salt)

: this(algorithm, password, salt, 1000) {

}

/// <summary>

/// Creates new instance.

/// </summary>

/// <param name="algorithm">HMAC algorithm to use.</param>

/// <param name="password">The password used to derive the key.</param>

/// <param name="salt">The key salt used to derive the key.</param>

/// <param name="iterations">The number of iterations for the operation.</param>

/// <exception cref="System.ArgumentNullException">Algorithm cannot be null - Password cannot be null. -or- Salt cannot be null.</exception>

public Pbkdf2(HMAC algorithm, String password, String salt, Int32 iterations) :

this(algorithm, UTF8Encoding.UTF8.GetBytes(password), UTF8Encoding.UTF8.GetBytes(salt), iterations) {

}

/// <summary>

/// Creates new instance.

/// </summary>

/// <param name="algorithm">HMAC algorithm to use.</param>

/// <param name="password">The password used to derive the key.</param>

/// <param name="salt">The key salt used to derive the key.</param>

/// <exception cref="System.ArgumentNullException">Algorithm cannot be null - Password cannot be null. -or- Salt cannot be null.</exception>

public Pbkdf2(HMAC algorithm, String password, String salt) :

this(algorithm, password, salt, 1000) {

}

private readonly int BlockSize;

private uint BlockIndex = 1;

private byte[] BufferBytes;

private int BufferStartIndex = 0;

private int BufferEndIndex = 0;

/// <summary>

/// Gets algorithm used for generating key.

/// </summary>

public HMAC Algorithm { get; private set; }

/// <summary>

/// Gets salt bytes.

/// </summary>

[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Performance", "CA1819:PropertiesShouldNotReturnArrays", Justification = "Byte array is proper return value in this case.")]

public Byte[] Salt { get; private set; }

/// <summary>

/// Gets iteration count.

/// </summary>

public Int32 IterationCount { get; private set; }

/// <summary>

/// Returns a pseudo-random key from a password, salt and iteration count.

/// </summary>

/// <param name="count">Number of bytes to return.</param>

/// <returns>Byte array.</returns>

///

public Byte[] GetBytes(int count, string algorithm = "sha512") {

byte[] result = new byte[count];

int resultOffset = 0;

int bufferCount = this.BufferEndIndex - this.BufferStartIndex;

if (bufferCount > 0) { //if there is some data in buffer

if (count < bufferCount) { //if there is enough data in buffer

Buffer.BlockCopy(this.BufferBytes, this.BufferStartIndex, result, 0, count);

this.BufferStartIndex += count;

return result;

}

Buffer.BlockCopy(this.BufferBytes, this.BufferStartIndex, result, 0, bufferCount);

this.BufferStartIndex = this.BufferEndIndex = 0;

resultOffset += bufferCount;

}

while (resultOffset < count) {

int needCount = count - resultOffset;

if (algorithm.ToLower() == "sha256")

this.BufferBytes = this.Func(false);

else

this.BufferBytes = this.Func();

if (needCount > this.BlockSize) { //we one (or more) additional passes

Buffer.BlockCopy(this.BufferBytes, 0, result, resultOffset, this.BlockSize);

resultOffset += this.BlockSize;

} else {

Buffer.BlockCopy(this.BufferBytes, 0, result, resultOffset, needCount);

this.BufferStartIndex = needCount;

this.BufferEndIndex = this.BlockSize;

return result;

}

}

return result;

}

private byte[] Func(bool mscrypto = true) {

var hash1Input = new byte[this.Salt.Length + 4];

Buffer.BlockCopy(this.Salt, 0, hash1Input, 0, this.Salt.Length);

Buffer.BlockCopy(GetBytesFromInt(this.BlockIndex), 0, hash1Input, this.Salt.Length, 4);

var hash1 = this.Algorithm.ComputeHash(hash1Input);

byte[] finalHash = hash1;

for (int i = 2; i <= this.IterationCount; i++) {

hash1 = this.Algorithm.ComputeHash(hash1, 0, hash1.Length);

for (int j = 0; j < this.BlockSize; j++) {

finalHash[j] = (byte)(finalHash[j] ^ hash1[j]);

}

if (mscrypto)

Array.Copy(finalHash, hash1, hash1.Length); // "thank you MS!" -@gentilkiwi

// https://github.com/gentilkiwi/mimikatz/blob/110a831ebe7b529c5dd3010f9e7fced0d3e3a46c/modules/kull_m_crypto.c#L207

}

if (this.BlockIndex == uint.MaxValue) { throw new InvalidOperationException("Derived key too long."); }

this.BlockIndex += 1;

return finalHash;

}

private static byte[] GetBytesFromInt(uint i) {

var bytes = BitConverter.GetBytes(i);

if (BitConverter.IsLittleEndian) {

return new byte[] { bytes[3], bytes[2], bytes[1], bytes[0] };

} else {

return bytes;

}

}

}

}