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package org.spongycastle.crypto.generators;
import org.spongycastle.crypto.PBEParametersGenerator;
import org.spongycastle.crypto.digests.SHA256Digest;
import org.spongycastle.crypto.engines.Salsa20Engine;
import org.spongycastle.crypto.params.KeyParameter;
import org.spongycastle.util.Arrays;
import org.spongycastle.util.Pack;
/**
* Implementation of the scrypt a password-based key derivation function.
* <p>
* 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>
*
*/
public class SCrypt
{
/**
* 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
* <code>2^(128 * r / 8)</code>.
* @param r the block size, must be >= 1.
* @param p Parallelization parameter. Must be a positive integer less than or equal to
* <code>Integer.MAX_VALUE / (128 * r * 8)</code>.
*
* @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)
{
throw new IllegalArgumentException("Cost parameter N must be > 1.");
}
// 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);
int MFLenWords = MFLenBytes >>> 2;
for (int BOff = 0; BOff < BLen; BOff += MFLenWords)
{
// TODO These can be done in parallel threads
SMix(B, BOff, N, 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 r)
{
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[][] V = new int[N][];
try
{
System.arraycopy(B, BOff, X, 0, BCount);
for (int i = 0; i < N; ++i)
{
V[i] = Arrays.clone(X);
BlockMix(X, blockX1, blockX2, blockY, r);
}
int mask = N - 1;
for (int i = 0; i < N; ++i)
{
int j = X[BCount - 16] & mask;
Xor(X, V[j], 0, X);
BlockMix(X, blockX1, blockX2, blockY, r);
}
System.arraycopy(X, 0, B, BOff, BCount);
}
finally
{
ClearAll(V);
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;
}
System.arraycopy(Y, 0, B, 0, Y.length);
}
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]);
}
}
}
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