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using System;
using System.Diagnostics;
using Org.BouncyCastle.Crypto.Digests;
using Org.BouncyCastle.Crypto.Engines;
using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Crypto.Utilities;
using Org.BouncyCastle.Math.Raw;
using Org.BouncyCastle.Utilities;
namespace Org.BouncyCastle.Crypto.Generators
{
/// <summary>Implementation of the scrypt a password-based key derivation function.</summary>
/// <remarks>
/// Scrypt was created by Colin Percival and is specified in
/// <a href="http://tools.ietf.org/html/draft-josefsson-scrypt-kdf-01">draft-josefsson-scrypt-kd</a>.
/// </remarks>
public class SCrypt
{
/// <summary>Generate a key using the scrypt key derivation function.</summary>
/// <param name="P">the bytes of the pass phrase.</param>
/// <param name="S">the salt to use for this invocation.</param>
/// <param name="N">CPU/Memory cost parameter. Must be larger than 1, a power of 2 and less than
/// <code>2^(128 * r / 8)</code>.</param>
/// <param name="r">the block size, must be >= 1.</param>
/// <param name="p">Parallelization parameter. Must be a positive integer less than or equal to
/// <code>int.MaxValue / (128 * r * 8)</code>.</param>
/// <param name="dkLen">the length of the key to generate.</param>
/// <returns>the generated key.</returns>
public static byte[] Generate(byte[] P, byte[] S, int N, int r, int p, int dkLen)
{
if (P == null)
throw new ArgumentNullException("Passphrase P must be provided.");
if (S == null)
throw new ArgumentNullException("Salt S must be provided.");
if (N <= 1 || !IsPowerOf2(N))
throw new ArgumentException("Cost parameter N must be > 1 and a power of 2.");
// Only value of r that cost (as an int) could be exceeded for is 1
if (r == 1 && N >= 65536)
throw new ArgumentException("Cost parameter N must be > 1 and < 65536.");
if (r < 1)
throw new ArgumentException("Block size r must be >= 1.");
int maxParallel = int.MaxValue / (128 * r * 8);
if (p < 1 || p > maxParallel)
{
throw new ArgumentException("Parallelisation parameter p must be >= 1 and <= " + maxParallel
+ " (based on block size r of " + r + ")");
}
if (dkLen < 1)
throw new ArgumentException("Generated key length dkLen must be >= 1.");
return MFcrypt(P, S, N, r, p, dkLen);
}
private static byte[] MFcrypt(byte[] P, byte[] S, int N, int r, int p, int dkLen)
{
int MFLenBytes = r * 128;
byte[] bytes = SingleIterationPBKDF2(P, S, p * MFLenBytes);
uint[] B = null;
try
{
int BLen = bytes.Length >> 2;
B = new uint[BLen];
Pack.LE_To_UInt32(bytes, 0, B);
/*
* Chunk memory allocations; We choose 'd' so that there will be 2**d chunks, each not
* larger than 32KiB, except that the minimum chunk size is 2 * r * 32.
*/
int d = 0, total = N * r;
while ((N - d) > 2 && total > (1 << 10))
{
++d;
total >>= 1;
}
int MFLenWords = MFLenBytes >> 2;
for (int BOff = 0; BOff < BLen; BOff += MFLenWords)
{
// TODO These can be done in parallel threads
SMix(B, BOff, N, d, r);
}
Pack.UInt32_To_LE(B, bytes, 0);
return SingleIterationPBKDF2(P, bytes, dkLen);
}
finally
{
ClearAll(bytes, B);
}
}
private static byte[] SingleIterationPBKDF2(byte[] P, byte[] S, int dkLen)
{
PbeParametersGenerator pGen = new Pkcs5S2ParametersGenerator(new Sha256Digest());
pGen.Init(P, S, 1);
KeyParameter key = (KeyParameter)pGen.GenerateDerivedMacParameters(dkLen * 8);
return key.GetKey();
}
private static void SMix(uint[] B, int BOff, int N, int d, int r)
{
int powN = Integers.NumberOfTrailingZeros(N);
int blocksPerChunk = N >> d;
int chunkCount = 1 << d, chunkMask = blocksPerChunk - 1, chunkPow = powN - d;
int BCount = r * 32;
uint[] blockX1 = new uint[16];
uint[] blockX2 = new uint[16];
uint[] blockY = new uint[BCount];
uint[] X = new uint[BCount];
uint[][] VV = new uint[chunkCount][];
try
{
Array.Copy(B, BOff, X, 0, BCount);
for (int c = 0; c < chunkCount; ++c)
{
uint[] V = new uint[blocksPerChunk * BCount];
VV[c] = V;
int off = 0;
for (int i = 0; i < blocksPerChunk; i += 2)
{
Array.Copy(X, 0, V, off, BCount);
off += BCount;
BlockMix(X, blockX1, blockX2, blockY, r);
Array.Copy(blockY, 0, V, off, BCount);
off += BCount;
BlockMix(blockY, blockX1, blockX2, X, r);
}
}
uint mask = (uint)N - 1;
for (int i = 0; i < N; ++i)
{
int j = (int)(X[BCount - 16] & mask);
uint[] V = VV[j >> chunkPow];
int VOff = (j & chunkMask) * BCount;
Nat.Xor(BCount, V, VOff, X, 0, blockY, 0);
BlockMix(blockY, blockX1, blockX2, X, r);
}
Array.Copy(X, 0, B, BOff, BCount);
}
finally
{
ClearAll(VV);
ClearAll(X, blockX1, blockX2, blockY);
}
}
private static void BlockMix(uint[] B, uint[] X1, uint[] X2, uint[] Y, int r)
{
Array.Copy(B, B.Length - 16, X1, 0, 16);
int BOff = 0, YOff = 0, halfLen = B.Length >> 1;
for (int i = 2 * r; i > 0; --i)
{
Nat512.Xor(X1, 0, B, BOff, X2, 0);
Salsa20Engine.SalsaCore(8, X2, X1);
Array.Copy(X1, 0, Y, YOff, 16);
YOff = halfLen + BOff - YOff;
BOff += 16;
}
}
private static void Clear(Array array)
{
if (array != null)
{
Array.Clear(array, 0, array.Length);
}
}
private static void ClearAll(params Array[] arrays)
{
foreach (Array array in arrays)
{
Clear(array);
}
}
// note: we know X is non-zero
private static bool IsPowerOf2(int x)
{
Debug.Assert(x != 0);
return (x & (x - 1)) == 0;
}
}
}
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