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package org.bouncycastle.crypto.generators;
import org.bouncycastle.crypto.PBEParametersGenerator;
import org.bouncycastle.crypto.digests.SHA256Digest;
import org.bouncycastle.crypto.engines.Salsa20Engine;
import org.bouncycastle.crypto.params.KeyParameter;
import org.bouncycastle.util.Arrays;
import org.bouncycastle.util.Integers;
import org.bouncycastle.util.Pack;
/**
* Implementation of the scrypt a password-based key derivation function.
*
* Scrypt was created by Colin Percival and is specified in RFC 7914 - The scrypt Password-Based Key Derivation Function
*/
public class SCrypt
{
private SCrypt()
{
// not used.
}
/**
* Generate a key using the scrypt key derivation function.
*
* @param P the bytes of the pass phrase.
* @param S the salt to use for this invocation.
* @param N CPU/Memory cost parameter. Must be larger than 1, a power of 2 and less than
* 2^(128 * r / 8).
* @param r the block size, must be >= 1.
* @param p Parallelization parameter. Must be a positive integer less than or equal to
* Integer.MAX_VALUE / (128 * r * 8).
* @param dkLen the length of the key to generate.
* @return the generated key.
*/
public static byte[] generate(byte[] P, byte[] S, int N, int r, int p, int dkLen)
{
if (P == null)
{
throw new IllegalArgumentException("Passphrase P must be provided.");
}
if (S == null)
{
throw new IllegalArgumentException("Salt S must be provided.");
}
if (N <= 1 || !isPowerOf2(N))
{
throw new IllegalArgumentException("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 IllegalArgumentException("Cost parameter N must be > 1 and < 65536.");
}
if (r < 1)
{
throw new IllegalArgumentException("Block size r must be >= 1.");
}
int maxParallel = Integer.MAX_VALUE / (128 * r * 8);
if (p < 1 || p > maxParallel)
{
throw new IllegalArgumentException("Parallelisation parameter p must be >= 1 and <= " + maxParallel
+ " (based on block size r of " + r + ")");
}
if (dkLen < 1)
{
throw new IllegalArgumentException("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);
int[] B = null;
try
{
int BLen = bytes.length >>> 2;
B = new int[BLen];
Pack.littleEndianToInt(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.intToLittleEndian(B, bytes, 0);
return SingleIterationPBKDF2(P, bytes, dkLen);
}
finally
{
Clear(bytes);
Clear(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(int[] 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;
int[] blockX1 = new int[16];
int[] blockX2 = new int[16];
int[] blockY = new int[BCount];
int[] X = new int[BCount];
int[][] VV = new int[chunkCount][];
try
{
System.arraycopy(B, BOff, X, 0, BCount);
for (int c = 0; c < chunkCount; ++c)
{
int[] V = new int[blocksPerChunk * BCount];
VV[c] = V;
int off = 0;
for (int i = 0; i < blocksPerChunk; i += 2)
{
System.arraycopy(X, 0, V, off, BCount);
off += BCount;
BlockMix(X, blockX1, blockX2, blockY, r);
System.arraycopy(blockY, 0, V, off, BCount);
off += BCount;
BlockMix(blockY, blockX1, blockX2, X, r);
}
}
int mask = N - 1;
for (int i = 0; i < N; ++i)
{
int j = X[BCount - 16] & mask;
int[] V = VV[j >>> chunkPow];
int VOff = (j & chunkMask) * BCount;
System.arraycopy(V, VOff, blockY, 0, BCount);
Xor(blockY, X, 0, blockY);
BlockMix(blockY, blockX1, blockX2, X, r);
}
System.arraycopy(X, 0, B, BOff, BCount);
}
finally
{
ClearAll(VV);
ClearAll(new int[][]{X, blockX1, blockX2, blockY});
}
}
private static void BlockMix(int[] B, int[] X1, int[] X2, int[] Y, int r)
{
System.arraycopy(B, B.length - 16, X1, 0, 16);
int BOff = 0, YOff = 0, halfLen = B.length >>> 1;
for (int i = 2 * r; i > 0; --i)
{
Xor(X1, B, BOff, X2);
Salsa20Engine.salsaCore(8, X2, X1);
System.arraycopy(X1, 0, Y, YOff, 16);
YOff = halfLen + BOff - YOff;
BOff += 16;
}
}
private static void Xor(int[] a, int[] b, int bOff, int[] output)
{
for (int i = output.length - 1; i >= 0; --i)
{
output[i] = a[i] ^ b[bOff + i];
}
}
private static void Clear(byte[] array)
{
if (array != null)
{
Arrays.fill(array, (byte)0);
}
}
private static void Clear(int[] array)
{
if (array != null)
{
Arrays.fill(array, 0);
}
}
private static void ClearAll(int[][] arrays)
{
for (int i = 0; i < arrays.length; ++i)
{
Clear(arrays[i]);
}
}
// note: we know X is non-zero
private static boolean isPowerOf2(int x)
{
return ((x & (x - 1)) == 0);
}
}