+// Copyright (C) 2011 - Will Glozer. All rights reserved.
+
+package com.lambdaworks.crypto;
+
+import javax.crypto.Mac;
+import javax.crypto.spec.SecretKeySpec;
+import java.security.GeneralSecurityException;
+import static java.lang.System.arraycopy;
+
+/**
+ * An implementation of the Password-Based Key Derivation Function as specified
+ * in RFC 2898.
+ *
+ * @author Will Glozer
+ */
+public class PBKDF {
+ /**
+ * Implementation of PBKDF2 (RFC2898).
+ *
+ * @param alg HMAC algorithm to use.
+ * @param P Password.
+ * @param S Salt.
+ * @param c Iteration count.
+ * @param dkLen Intended length, in octets, of the derived key.
+ *
+ * @return The derived key.
+ *
+ * @throws GeneralSecurityException
+ */
+ public static byte[] pbkdf2(String alg, byte[] P, byte[] S, int c, int dkLen) throws GeneralSecurityException {
+ Mac mac = Mac.getInstance(alg);
+ mac.init(new SecretKeySpec(P, alg));
+ byte[] DK = new byte[dkLen];
+ pbkdf2(mac, S, c, DK, dkLen);
+ return DK;
+ }
+
+ /**
+ * Implementation of PBKDF2 (RFC2898).
+ *
+ * @param mac Pre-initialized {@link Mac} instance to use.
+ * @param S Salt.
+ * @param c Iteration count.
+ * @param DK Byte array that derived key will be placed in.
+ * @param dkLen Intended length, in octets, of the derived key.
+ *
+ * @throws GeneralSecurityException
+ */
+ public static void pbkdf2(Mac mac, byte[] S, int c, byte[] DK, int dkLen) throws GeneralSecurityException {
+ int hLen = mac.getMacLength();
+
+ if (dkLen > (Math.pow(2, 32) - 1) * hLen) {
+ throw new GeneralSecurityException("Requested key length too long");
+ }
+
+ byte[] U = new byte[hLen];
+ byte[] T = new byte[hLen];
+ byte[] block1 = new byte[S.length + 4];
+
+ int l = (int) Math.ceil((double) dkLen / hLen);
+ int r = dkLen - (l - 1) * hLen;
+
+ arraycopy(S, 0, block1, 0, S.length);
+
+ for (int i = 1; i <= l; i++) {
+ block1[S.length + 0] = (byte) (i >> 24 & 0xff);
+ block1[S.length + 1] = (byte) (i >> 16 & 0xff);
+ block1[S.length + 2] = (byte) (i >> 8 & 0xff);
+ block1[S.length + 3] = (byte) (i >> 0 & 0xff);
+
+ mac.update(block1);
+ mac.doFinal(U, 0);
+ arraycopy(U, 0, T, 0, hLen);
+
+ for (int j = 1; j < c; j++) {
+ mac.update(U);
+ mac.doFinal(U, 0);
+
+ for (int k = 0; k < hLen; k++) {
+ T[k] ^= U[k];
+ }
+ }
+
+ arraycopy(T, 0, DK, (i - 1) * hLen, (i == l ? r : hLen));
+ }
+ }
+}