src/java.security.jgss/share/classes/sun/security/krb5/internal/crypto/dk/AesSha2DkCrypto.java - platform/libcore - Git at Google

 /*
  * Copyright (c) 2017, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License version 2 only, as
  * published by the Free Software Foundation.  Oracle designates this
  * particular file as subject to the "Classpath" exception as provided
  * by Oracle in the LICENSE file that accompanied this code.
  *
  * This code is distributed in the hope that it will be useful, but WITHOUT
  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  * version 2 for more details (a copy is included in the LICENSE file that
  * accompanied this code).
  *
  * You should have received a copy of the GNU General Public License version
  * 2 along with this work; if not, write to the Free Software Foundation,
  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  *
  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  * or visit www.oracle.com if you need additional information or have any
  * questions.
  */

 /*
  */

 package sun.security.krb5.internal.crypto.dk;

 import javax.crypto.Cipher;
 import javax.crypto.Mac;
 import javax.crypto.SecretKeyFactory;
 import javax.crypto.SecretKey;
 import javax.crypto.spec.SecretKeySpec;
 import javax.crypto.spec.IvParameterSpec;
 import javax.crypto.spec.PBEKeySpec;
 import java.security.GeneralSecurityException;
 import sun.security.krb5.KrbCryptoException;
 import sun.security.krb5.Confounder;
 import sun.security.krb5.internal.crypto.KeyUsage;
 import java.util.Arrays;

 /**
  * This class provides the implementation of AES Encryption with
  * HMAC-SHA2 for Kerberos 5
  * https://tools.ietf.org/html/rfc8009
  *
  * Algorithm profile described in [KCRYPTO]:
  * +--------------------------------------------------------------------+
  * |               protocol key format          128- or 256-bit string  |
  * |                                                                    |
  * |            string-to-key function          PBKDF2+DK with variable |
  * |                                          iteration count (see      |
  * |                                          above)                    |
  * |                                                                    |
  * |  default string-to-key parameters          00 00 80 00             |
  * |                                                                    |
  * |        key-generation seed length          key size                |
  * |                                                                    |
  * |            random-to-key function          identity function       |
  * |                                                                    |
  * |                  hash function, H          SHA-256 / SHA-384       |
  * |                                                                    |
  * |               HMAC output size, h          16/24 octets            |
  * |                                                                    |
  * |             message block size, m          1 octet                 |
  * |                                                                    |
  * |  encryption/decryption functions,          AES in CBC-CTS mode     |
  * |  E and D                                 (cipher block size 16     |
  * |                                          octets), with next to     |
  * |                                          last block as CBC-style   |
  * |                                          ivec                      |
  * +--------------------------------------------------------------------+
  *
  * Supports aes128-cts-hmac-sha256-128 and aes256-cts-hmac-sha384-192
  */

 public class AesSha2DkCrypto extends DkCrypto {

     private static final boolean debug = false;

     private static final int BLOCK_SIZE = 16;
     private static final int DEFAULT_ITERATION_COUNT = 32768;
     private static final byte[] ZERO_IV = new byte[] { 0, 0, 0, 0, 0, 0, 0, 0,
                                                        0, 0, 0, 0, 0, 0, 0, 0 };

     private static final byte[] ETYPE_NAME_128 =
             "aes128-cts-hmac-sha256-128".getBytes();
     private static final byte[] ETYPE_NAME_256 =
             "aes256-cts-hmac-sha384-192".getBytes();

     private final int hashSize;
     private final int keyLength;

     public AesSha2DkCrypto(int length) {
         keyLength = length;
         hashSize = (length == 128?128:192)/8;
     }

     protected int getKeySeedLength() {
         return keyLength;   // bits; AES key material
     }

     public byte[] stringToKey(char[] password, String salt, byte[] s2kparams)
         throws GeneralSecurityException {

         byte[] saltUtf8 = null;
         try {
             saltUtf8 = salt.getBytes("UTF-8");
             return stringToKey(password, saltUtf8, s2kparams);
         } catch (Exception e) {
             return null;
         } finally {
             if (saltUtf8 != null) {
                 Arrays.fill(saltUtf8, (byte)0);
             }
         }
     }

     // https://tools.ietf.org/html/rfc8009#section-4
     private byte[] stringToKey(char[] secret, byte[] salt, byte[] params)
         throws GeneralSecurityException {

         int iter_count = DEFAULT_ITERATION_COUNT;
         if (params != null) {
             if (params.length != 4) {
                 throw new RuntimeException("Invalid parameter to stringToKey");
             }
             iter_count = readBigEndian(params, 0, 4);
         }

         byte[] saltp = new byte[26 + 1 + salt.length];
         if (keyLength == 128) {
             System.arraycopy(ETYPE_NAME_128, 0, saltp, 0, 26);
         } else {
             System.arraycopy(ETYPE_NAME_256, 0, saltp, 0, 26);
         }
         System.arraycopy(salt, 0, saltp, 27, salt.length);
         byte[] tmpKey = randomToKey(PBKDF2(secret, saltp, iter_count,
                                         getKeySeedLength()));
         byte[] result = dk(tmpKey, KERBEROS_CONSTANT);
         return result;
     }

     protected byte[] randomToKey(byte[] in) {
         // simple identity operation
         return in;
     }

     /*
      * https://tools.ietf.org/html/rfc8009#section-3 defines
      * a new key derivation function:
      *
      * KDF-HMAC-SHA2(key, label, k) = k-truncate(K1)
      * K1 = HMAC-SHA-256(key, 0x00000001 | label | 0x00 | k) or
      * K1 = HMAC-SHA-384(key, 0x00000001 | label | 0x00 | k)
      *
      * where label is constant below.
      */
     protected byte[] dr(byte[] key, byte[] constant)
             throws GeneralSecurityException {
         byte[] result;
         byte[] input = new byte[constant.length + 9];
         // 0x00000001 at the beginning
         input[3] = 1;
         // label follows
         System.arraycopy(constant, 0, input, 4, constant.length);
         SecretKeySpec tkey = new SecretKeySpec(key, "HMAC");
         Mac mac = Mac.getInstance(
                 keyLength == 128? "HmacSHA256": "HmacSHA384");
         mac.init(tkey);

         int k;
         if (keyLength == 128) {
             // key length for enc and hmac both 128
             k = 128;
         } else {
             byte last = constant[constant.length-1];
             if (last == (byte)0x99 || last == (byte)0x55) {
                 // 192 for hmac
                 k = 192;
             } else {
                 // 256 for enc
                 k = 256;
             }
         }
         // 0x00 and k at the end
         input[input.length - 1] = (byte)(k);
         input[input.length - 2] = (byte)(k / 256);

         result = mac.doFinal(input);
         return Arrays.copyOf(result, k / 8);
     }

     protected Cipher getCipher(byte[] key, byte[] ivec, int mode)
         throws GeneralSecurityException {

         // IV
         if (ivec == null) {
            ivec = ZERO_IV;
         }
         SecretKeySpec secretKey = new SecretKeySpec(key, "AES");
         Cipher cipher = Cipher.getInstance("AES/CBC/NoPadding");
         IvParameterSpec encIv = new IvParameterSpec(ivec, 0, ivec.length);
         cipher.init(mode, secretKey, encIv);
         return cipher;
     }

     // get an instance of the AES Cipher in CTS mode
     public int getChecksumLength() {
         return hashSize;  // bytes
     }

     /**
      * Get the truncated HMAC
      */
     protected byte[] getHmac(byte[] key, byte[] msg)
         throws GeneralSecurityException {

         SecretKey keyKi = new SecretKeySpec(key, "HMAC");
         Mac m = Mac.getInstance(keyLength == 128 ? "HmacSHA256" : "HmacSHA384");
         m.init(keyKi);

         // generate hash
         byte[] hash = m.doFinal(msg);

         // truncate hash
         byte[] output = new byte[hashSize];
         System.arraycopy(hash, 0, output, 0, hashSize);
         return output;
     }

     private byte[] deriveKey(byte[] baseKey, int usage, byte type)
             throws GeneralSecurityException {
         byte[] constant = new byte[5];
         constant[0] = (byte) ((usage>>24)&0xff);
         constant[1] = (byte) ((usage>>16)&0xff);
         constant[2] = (byte) ((usage>>8)&0xff);
         constant[3] = (byte) (usage&0xff);
         constant[4] = type;
         return dk(baseKey, constant);
     }

     /**
      * Calculate the checksum
      */
     public byte[] calculateChecksum(byte[] baseKey, int usage, byte[] input,
         int start, int len) throws GeneralSecurityException {

         if (!KeyUsage.isValid(usage)) {
             throw new GeneralSecurityException("Invalid key usage number: "
                                                 + usage);
         }

         byte[] Kc = deriveKey(baseKey, usage, (byte) 0x99);  // Checksum key
         if (debug) {
             System.err.println("usage: " + usage);
             traceOutput("input", input, start, Math.min(len, 32));
             traceOutput("baseKey", baseKey, 0, baseKey.length);
             traceOutput("Kc", Kc, 0, Kc.length);
         }

         try {
             // Generate checksum
             // H1 = HMAC(Kc, input)
             byte[] hmac = getHmac(Kc, input);
             if (debug) {
                 traceOutput("hmac", hmac, 0, hmac.length);
             }
             if (hmac.length == getChecksumLength()) {
                 return hmac;
             } else if (hmac.length > getChecksumLength()) {
                 byte[] buf = new byte[getChecksumLength()];
                 System.arraycopy(hmac, 0, buf, 0, buf.length);
                 return buf;
             } else {
                 throw new GeneralSecurityException("checksum size too short: " +
                         hmac.length + "; expecting : " + getChecksumLength());
             }
         } finally {
             Arrays.fill(Kc, 0, Kc.length, (byte)0);
         }
     }

     /**
      * Performs encryption using derived key; adds confounder.
      */
     public byte[] encrypt(byte[] baseKey, int usage,
         byte[] ivec, byte[] new_ivec, byte[] plaintext, int start, int len)
         throws GeneralSecurityException, KrbCryptoException {

         if (!KeyUsage.isValid(usage)) {
             throw new GeneralSecurityException("Invalid key usage number: "
                                                  + usage);
         }
         byte[] output = encryptCTS(baseKey, usage, ivec, new_ivec, plaintext,
                                         start, len, true);
         return output;
     }

     /**
      * Performs encryption using derived key; does not add confounder.
      */
     public byte[] encryptRaw(byte[] baseKey, int usage,
         byte[] ivec, byte[] plaintext, int start, int len)
         throws GeneralSecurityException, KrbCryptoException {

         if (!KeyUsage.isValid(usage)) {
             throw new GeneralSecurityException("Invalid key usage number: "
                                                 + usage);
         }
         byte[] output = encryptCTS(baseKey, usage, ivec, null, plaintext,
                                         start, len, false);
         return output;
     }

     /**
      * @param baseKey key from which keys are to be derived using usage
      * @param ciphertext  E(Ke, conf | plaintext | padding, ivec) | H1[1..h]
      */
     public byte[] decrypt(byte[] baseKey, int usage, byte[] ivec,
         byte[] ciphertext, int start, int len) throws GeneralSecurityException {

         if (!KeyUsage.isValid(usage)) {
             throw new GeneralSecurityException("Invalid key usage number: "
                                                 + usage);
         }
         byte[] output = decryptCTS(baseKey, usage, ivec, ciphertext,
                                         start, len, true);
         return output;
     }

     /**
      * Decrypts data using specified key and initial vector.
      * @param baseKey encryption key to use
      * @param ciphertext  encrypted data to be decrypted
      * @param usage ignored
      */
     public byte[] decryptRaw(byte[] baseKey, int usage, byte[] ivec,
         byte[] ciphertext, int start, int len)
         throws GeneralSecurityException {

         if (!KeyUsage.isValid(usage)) {
             throw new GeneralSecurityException("Invalid key usage number: "
                                                 + usage);
         }
         byte[] output = decryptCTS(baseKey, usage, ivec, ciphertext,
                                         start, len, false);
         return output;
     }

     /**
      * Encrypt AES in CBC-CTS mode using derived keys.
      */
     private byte[] encryptCTS(byte[] baseKey, int usage, byte[] ivec,
         byte[] new_ivec, byte[] plaintext, int start, int len,
         boolean confounder_exists)
         throws GeneralSecurityException, KrbCryptoException {

         byte[] Ke = null;
         byte[] Ki = null;

         if (debug) {
             System.err.println("usage: " + usage);
             if (ivec != null) {
                 traceOutput("old_state.ivec", ivec, 0, ivec.length);
             }
             traceOutput("plaintext", plaintext, start, Math.min(len, 32));
             traceOutput("baseKey", baseKey, 0, baseKey.length);
         }

         try {
             Ke = deriveKey(baseKey, usage, (byte) 0xaa);  // Encryption key

             byte[] toBeEncrypted = null;
             if (confounder_exists) {
                 byte[] confounder = Confounder.bytes(BLOCK_SIZE);
                 toBeEncrypted = new byte[confounder.length + len];
                 System.arraycopy(confounder, 0, toBeEncrypted,
                                         0, confounder.length);
                 System.arraycopy(plaintext, start, toBeEncrypted,
                                         confounder.length, len);
             } else {
                 toBeEncrypted = new byte[len];
                 System.arraycopy(plaintext, start, toBeEncrypted, 0, len);
             }

             // encryptedData + HMAC
             byte[] output = new byte[toBeEncrypted.length + hashSize];

             // AES in JCE
             Cipher cipher = Cipher.getInstance("AES/CTS/NoPadding");
             SecretKeySpec secretKey = new SecretKeySpec(Ke, "AES");
             IvParameterSpec encIv = new IvParameterSpec(ivec, 0, ivec.length);
             cipher.init(Cipher.ENCRYPT_MODE, secretKey, encIv);
             cipher.doFinal(toBeEncrypted, 0, toBeEncrypted.length, output);

             Ki = deriveKey(baseKey, usage, (byte) 0x55);
             if (debug) {
                 traceOutput("Ki", Ki, 0, Ke.length);
             }

             // Generate checksum
             // H = HMAC(Ki, IV | C)
             byte[] msg = Arrays.copyOf(ivec, ivec.length + toBeEncrypted.length);
             System.arraycopy(output, 0, msg, ivec.length, toBeEncrypted.length);
             byte[] hmac = getHmac(Ki, msg);

             // encryptedData + HMAC
             System.arraycopy(hmac, 0, output, toBeEncrypted.length,
                                 hmac.length);
             return output;
         } finally {
             if (Ke != null) {
                 Arrays.fill(Ke, 0, Ke.length, (byte) 0);
             }
             if (Ki != null) {
                 Arrays.fill(Ki, 0, Ki.length, (byte) 0);
             }
         }
     }

     /**
      * Decrypt AES in CBC-CTS mode using derived keys.
      */
     private byte[] decryptCTS(byte[] baseKey, int usage, byte[] ivec,
         byte[] ciphertext, int start, int len, boolean confounder_exists)
         throws GeneralSecurityException {

         byte[] Ke = null;
         byte[] Ki = null;

         try {
             Ke = deriveKey(baseKey, usage, (byte) 0xaa);  // Encryption key

             if (debug) {
                 System.err.println("usage: " + usage);
                 if (ivec != null) {
                     traceOutput("old_state.ivec", ivec, 0, ivec.length);
                 }
                 traceOutput("ciphertext", ciphertext, start, Math.min(len, 32));
                 traceOutput("baseKey", baseKey, 0, baseKey.length);
                 traceOutput("Ke", Ke, 0, Ke.length);
             }

             // Decrypt [confounder | plaintext ] (without checksum)

             // AES in JCE
             Cipher cipher = Cipher.getInstance("AES/CTS/NoPadding");
             SecretKeySpec secretKey = new SecretKeySpec(Ke, "AES");
             IvParameterSpec encIv = new IvParameterSpec(ivec, 0, ivec.length);
             cipher.init(Cipher.DECRYPT_MODE, secretKey, encIv);
             byte[] plaintext = cipher.doFinal(ciphertext, start, len-hashSize);

             if (debug) {
                 traceOutput("AES PlainText", plaintext, 0,
                                 Math.min(plaintext.length, 32));
             }

             Ki = deriveKey(baseKey, usage, (byte) 0x55);  // Integrity key
             if (debug) {
                 traceOutput("Ki", Ki, 0, Ke.length);
             }

             // Verify checksum
             // H = HMAC(Ki, IV | C)
             byte[] msg = Arrays.copyOf(ivec, ivec.length + len-hashSize);
             System.arraycopy(ciphertext, start, msg, ivec.length, len-hashSize);
             byte[] calculatedHmac = getHmac(Ki, msg);
             int hmacOffset = start + len - hashSize;
             if (debug) {
                 traceOutput("calculated Hmac", calculatedHmac,
                                 0, calculatedHmac.length);
                 traceOutput("message Hmac", ciphertext, hmacOffset, hashSize);
             }
             boolean cksumFailed = false;
             if (calculatedHmac.length >= hashSize) {
                 for (int i = 0; i < hashSize; i++) {
                     if (calculatedHmac[i] != ciphertext[hmacOffset+i]) {
                         cksumFailed = true;
                         if (debug) {
                             System.err.println("Checksum failed !");
                         }
                         break;
                     }
                 }
             }
             if (cksumFailed) {
                 throw new GeneralSecurityException("Checksum failed");
             }

             if (confounder_exists) {
                 // Get rid of confounder
                 // [ confounder | plaintext ]
                 byte[] output = new byte[plaintext.length - BLOCK_SIZE];
                 System.arraycopy(plaintext, BLOCK_SIZE, output,
                                         0, output.length);
                 return output;
             } else {
                 return plaintext;
             }
         } finally {
             if (Ke != null) {
                 Arrays.fill(Ke, 0, Ke.length, (byte) 0);
             }
             if (Ki != null) {
                 Arrays.fill(Ki, 0, Ki.length, (byte) 0);
             }
         }
     }

     /*
      * Invoke the PKCS#5 PBKDF2 algorithm
      */
     private static byte[] PBKDF2(char[] secret, byte[] salt,
         int count, int keyLength) throws GeneralSecurityException {

         PBEKeySpec keySpec = new PBEKeySpec(secret, salt, count, keyLength);
         SecretKeyFactory skf =
                 SecretKeyFactory.getInstance(keyLength == 128 ?
                         "PBKDF2WithHmacSHA256" : "PBKDF2WithHmacSHA384");
         SecretKey key = skf.generateSecret(keySpec);
         byte[] result = key.getEncoded();

         return result;
     }

     public static final int readBigEndian(byte[] data, int pos, int size) {
         int retVal = 0;
         int shifter = (size-1)*8;
         while (size > 0) {
             retVal += (data[pos] & 0xff) << shifter;
             shifter -= 8;
             pos++;
             size--;
         }
         return retVal;
     }

 }
	/*
	* Copyright (c) 2017, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	/*
	*/

	package sun.security.krb5.internal.crypto.dk;

	import javax.crypto.Cipher;
	import javax.crypto.Mac;
	import javax.crypto.SecretKeyFactory;
	import javax.crypto.SecretKey;
	import javax.crypto.spec.SecretKeySpec;
	import javax.crypto.spec.IvParameterSpec;
	import javax.crypto.spec.PBEKeySpec;
	import java.security.GeneralSecurityException;
	import sun.security.krb5.KrbCryptoException;
	import sun.security.krb5.Confounder;
	import sun.security.krb5.internal.crypto.KeyUsage;
	import java.util.Arrays;

	/**
	* This class provides the implementation of AES Encryption with
	* HMAC-SHA2 for Kerberos 5
	* https://tools.ietf.org/html/rfc8009
	*
	* Algorithm profile described in [KCRYPTO]:
	* +--------------------------------------------------------------------+
	* \| protocol key format 128- or 256-bit string \|
	* \| \|
	* \| string-to-key function PBKDF2+DK with variable \|
	* \| iteration count (see \|
	* \| above) \|
	* \| \|
	* \| default string-to-key parameters 00 00 80 00 \|
	* \| \|
	* \| key-generation seed length key size \|
	* \| \|
	* \| random-to-key function identity function \|
	* \| \|
	* \| hash function, H SHA-256 / SHA-384 \|
	* \| \|
	* \| HMAC output size, h 16/24 octets \|
	* \| \|
	* \| message block size, m 1 octet \|
	* \| \|
	* \| encryption/decryption functions, AES in CBC-CTS mode \|
	* \| E and D (cipher block size 16 \|
	* \| octets), with next to \|
	* \| last block as CBC-style \|
	* \| ivec \|
	* +--------------------------------------------------------------------+
	*
	* Supports aes128-cts-hmac-sha256-128 and aes256-cts-hmac-sha384-192
	*/

	public class AesSha2DkCrypto extends DkCrypto {

	private static final boolean debug = false;

	private static final int BLOCK_SIZE = 16;
	private static final int DEFAULT_ITERATION_COUNT = 32768;
	private static final byte[] ZERO_IV = new byte[] { 0, 0, 0, 0, 0, 0, 0, 0,
	0, 0, 0, 0, 0, 0, 0, 0 };

	private static final byte[] ETYPE_NAME_128 =
	"aes128-cts-hmac-sha256-128".getBytes();
	private static final byte[] ETYPE_NAME_256 =
	"aes256-cts-hmac-sha384-192".getBytes();

	private final int hashSize;
	private final int keyLength;

	public AesSha2DkCrypto(int length) {
	keyLength = length;
	hashSize = (length == 128?128:192)/8;
	}

	protected int getKeySeedLength() {
	return keyLength; // bits; AES key material
	}

	public byte[] stringToKey(char[] password, String salt, byte[] s2kparams)
	throws GeneralSecurityException {

	byte[] saltUtf8 = null;
	try {
	saltUtf8 = salt.getBytes("UTF-8");
	return stringToKey(password, saltUtf8, s2kparams);
	} catch (Exception e) {
	return null;
	} finally {
	if (saltUtf8 != null) {
	Arrays.fill(saltUtf8, (byte)0);
	}
	}
	}

	// https://tools.ietf.org/html/rfc8009#section-4
	private byte[] stringToKey(char[] secret, byte[] salt, byte[] params)
	throws GeneralSecurityException {

	int iter_count = DEFAULT_ITERATION_COUNT;
	if (params != null) {
	if (params.length != 4) {
	throw new RuntimeException("Invalid parameter to stringToKey");
	}
	iter_count = readBigEndian(params, 0, 4);
	}

	byte[] saltp = new byte[26 + 1 + salt.length];
	if (keyLength == 128) {
	System.arraycopy(ETYPE_NAME_128, 0, saltp, 0, 26);
	} else {
	System.arraycopy(ETYPE_NAME_256, 0, saltp, 0, 26);
	}
	System.arraycopy(salt, 0, saltp, 27, salt.length);
	byte[] tmpKey = randomToKey(PBKDF2(secret, saltp, iter_count,
	getKeySeedLength()));
	byte[] result = dk(tmpKey, KERBEROS_CONSTANT);
	return result;
	}

	protected byte[] randomToKey(byte[] in) {
	// simple identity operation
	return in;
	}

	/*
	* https://tools.ietf.org/html/rfc8009#section-3 defines
	* a new key derivation function:
	*
	* KDF-HMAC-SHA2(key, label, k) = k-truncate(K1)
	* K1 = HMAC-SHA-256(key, 0x00000001 \| label \| 0x00 \| k) or
	* K1 = HMAC-SHA-384(key, 0x00000001 \| label \| 0x00 \| k)
	*
	* where label is constant below.
	*/
	protected byte[] dr(byte[] key, byte[] constant)
	throws GeneralSecurityException {
	byte[] result;
	byte[] input = new byte[constant.length + 9];
	// 0x00000001 at the beginning
	input[3] = 1;
	// label follows
	System.arraycopy(constant, 0, input, 4, constant.length);
	SecretKeySpec tkey = new SecretKeySpec(key, "HMAC");
	Mac mac = Mac.getInstance(
	keyLength == 128? "HmacSHA256": "HmacSHA384");
	mac.init(tkey);

	int k;
	if (keyLength == 128) {
	// key length for enc and hmac both 128
	k = 128;
	} else {
	byte last = constant[constant.length-1];
	if (last == (byte)0x99 \|\| last == (byte)0x55) {
	// 192 for hmac
	k = 192;
	} else {
	// 256 for enc
	k = 256;
	}
	}
	// 0x00 and k at the end
	input[input.length - 1] = (byte)(k);
	input[input.length - 2] = (byte)(k / 256);

	result = mac.doFinal(input);
	return Arrays.copyOf(result, k / 8);
	}

	protected Cipher getCipher(byte[] key, byte[] ivec, int mode)
	throws GeneralSecurityException {

	// IV
	if (ivec == null) {
	ivec = ZERO_IV;
	}
	SecretKeySpec secretKey = new SecretKeySpec(key, "AES");
	Cipher cipher = Cipher.getInstance("AES/CBC/NoPadding");
	IvParameterSpec encIv = new IvParameterSpec(ivec, 0, ivec.length);
	cipher.init(mode, secretKey, encIv);
	return cipher;
	}

	// get an instance of the AES Cipher in CTS mode
	public int getChecksumLength() {
	return hashSize; // bytes
	}

	/**
	* Get the truncated HMAC
	*/
	protected byte[] getHmac(byte[] key, byte[] msg)
	throws GeneralSecurityException {

	SecretKey keyKi = new SecretKeySpec(key, "HMAC");
	Mac m = Mac.getInstance(keyLength == 128 ? "HmacSHA256" : "HmacSHA384");
	m.init(keyKi);

	// generate hash
	byte[] hash = m.doFinal(msg);

	// truncate hash
	byte[] output = new byte[hashSize];
	System.arraycopy(hash, 0, output, 0, hashSize);
	return output;
	}

	private byte[] deriveKey(byte[] baseKey, int usage, byte type)
	throws GeneralSecurityException {
	byte[] constant = new byte[5];
	constant[0] = (byte) ((usage>>24)&0xff);
	constant[1] = (byte) ((usage>>16)&0xff);
	constant[2] = (byte) ((usage>>8)&0xff);
	constant[3] = (byte) (usage&0xff);
	constant[4] = type;
	return dk(baseKey, constant);
	}

	/**
	* Calculate the checksum
	*/
	public byte[] calculateChecksum(byte[] baseKey, int usage, byte[] input,
	int start, int len) throws GeneralSecurityException {

	if (!KeyUsage.isValid(usage)) {
	throw new GeneralSecurityException("Invalid key usage number: "
	+ usage);
	}

	byte[] Kc = deriveKey(baseKey, usage, (byte) 0x99); // Checksum key
	if (debug) {
	System.err.println("usage: " + usage);
	traceOutput("input", input, start, Math.min(len, 32));
	traceOutput("baseKey", baseKey, 0, baseKey.length);
	traceOutput("Kc", Kc, 0, Kc.length);
	}

	try {
	// Generate checksum
	// H1 = HMAC(Kc, input)
	byte[] hmac = getHmac(Kc, input);
	if (debug) {
	traceOutput("hmac", hmac, 0, hmac.length);
	}
	if (hmac.length == getChecksumLength()) {
	return hmac;
	} else if (hmac.length > getChecksumLength()) {
	byte[] buf = new byte[getChecksumLength()];
	System.arraycopy(hmac, 0, buf, 0, buf.length);
	return buf;
	} else {
	throw new GeneralSecurityException("checksum size too short: " +
	hmac.length + "; expecting : " + getChecksumLength());
	}
	} finally {
	Arrays.fill(Kc, 0, Kc.length, (byte)0);
	}
	}

	/**
	* Performs encryption using derived key; adds confounder.
	*/
	public byte[] encrypt(byte[] baseKey, int usage,
	byte[] ivec, byte[] new_ivec, byte[] plaintext, int start, int len)
	throws GeneralSecurityException, KrbCryptoException {

	if (!KeyUsage.isValid(usage)) {
	throw new GeneralSecurityException("Invalid key usage number: "
	+ usage);
	}
	byte[] output = encryptCTS(baseKey, usage, ivec, new_ivec, plaintext,
	start, len, true);
	return output;
	}

	/**
	* Performs encryption using derived key; does not add confounder.
	*/
	public byte[] encryptRaw(byte[] baseKey, int usage,
	byte[] ivec, byte[] plaintext, int start, int len)
	throws GeneralSecurityException, KrbCryptoException {

	if (!KeyUsage.isValid(usage)) {
	throw new GeneralSecurityException("Invalid key usage number: "
	+ usage);
	}
	byte[] output = encryptCTS(baseKey, usage, ivec, null, plaintext,
	start, len, false);
	return output;
	}

	/**
	* @param baseKey key from which keys are to be derived using usage
	* @param ciphertext E(Ke, conf \| plaintext \| padding, ivec) \| H1[1..h]
	*/
	public byte[] decrypt(byte[] baseKey, int usage, byte[] ivec,
	byte[] ciphertext, int start, int len) throws GeneralSecurityException {

	if (!KeyUsage.isValid(usage)) {
	throw new GeneralSecurityException("Invalid key usage number: "
	+ usage);
	}
	byte[] output = decryptCTS(baseKey, usage, ivec, ciphertext,
	start, len, true);
	return output;
	}

	/**
	* Decrypts data using specified key and initial vector.
	* @param baseKey encryption key to use
	* @param ciphertext encrypted data to be decrypted
	* @param usage ignored
	*/
	public byte[] decryptRaw(byte[] baseKey, int usage, byte[] ivec,
	byte[] ciphertext, int start, int len)
	throws GeneralSecurityException {

	if (!KeyUsage.isValid(usage)) {
	throw new GeneralSecurityException("Invalid key usage number: "
	+ usage);
	}
	byte[] output = decryptCTS(baseKey, usage, ivec, ciphertext,
	start, len, false);
	return output;
	}

	/**
	* Encrypt AES in CBC-CTS mode using derived keys.
	*/
	private byte[] encryptCTS(byte[] baseKey, int usage, byte[] ivec,
	byte[] new_ivec, byte[] plaintext, int start, int len,
	boolean confounder_exists)
	throws GeneralSecurityException, KrbCryptoException {

	byte[] Ke = null;
	byte[] Ki = null;

	if (debug) {
	System.err.println("usage: " + usage);
	if (ivec != null) {
	traceOutput("old_state.ivec", ivec, 0, ivec.length);
	}
	traceOutput("plaintext", plaintext, start, Math.min(len, 32));
	traceOutput("baseKey", baseKey, 0, baseKey.length);
	}

	try {
	Ke = deriveKey(baseKey, usage, (byte) 0xaa); // Encryption key

	byte[] toBeEncrypted = null;
	if (confounder_exists) {
	byte[] confounder = Confounder.bytes(BLOCK_SIZE);
	toBeEncrypted = new byte[confounder.length + len];
	System.arraycopy(confounder, 0, toBeEncrypted,
	0, confounder.length);
	System.arraycopy(plaintext, start, toBeEncrypted,
	confounder.length, len);
	} else {
	toBeEncrypted = new byte[len];
	System.arraycopy(plaintext, start, toBeEncrypted, 0, len);
	}

	// encryptedData + HMAC
	byte[] output = new byte[toBeEncrypted.length + hashSize];

	// AES in JCE
	Cipher cipher = Cipher.getInstance("AES/CTS/NoPadding");
	SecretKeySpec secretKey = new SecretKeySpec(Ke, "AES");
	IvParameterSpec encIv = new IvParameterSpec(ivec, 0, ivec.length);
	cipher.init(Cipher.ENCRYPT_MODE, secretKey, encIv);
	cipher.doFinal(toBeEncrypted, 0, toBeEncrypted.length, output);

	Ki = deriveKey(baseKey, usage, (byte) 0x55);
	if (debug) {
	traceOutput("Ki", Ki, 0, Ke.length);
	}

	// Generate checksum
	// H = HMAC(Ki, IV \| C)
	byte[] msg = Arrays.copyOf(ivec, ivec.length + toBeEncrypted.length);
	System.arraycopy(output, 0, msg, ivec.length, toBeEncrypted.length);
	byte[] hmac = getHmac(Ki, msg);

	// encryptedData + HMAC
	System.arraycopy(hmac, 0, output, toBeEncrypted.length,
	hmac.length);
	return output;
	} finally {
	if (Ke != null) {
	Arrays.fill(Ke, 0, Ke.length, (byte) 0);
	}
	if (Ki != null) {
	Arrays.fill(Ki, 0, Ki.length, (byte) 0);
	}
	}
	}

	/**
	* Decrypt AES in CBC-CTS mode using derived keys.
	*/
	private byte[] decryptCTS(byte[] baseKey, int usage, byte[] ivec,
	byte[] ciphertext, int start, int len, boolean confounder_exists)
	throws GeneralSecurityException {

	byte[] Ke = null;
	byte[] Ki = null;

	try {
	Ke = deriveKey(baseKey, usage, (byte) 0xaa); // Encryption key

	if (debug) {
	System.err.println("usage: " + usage);
	if (ivec != null) {
	traceOutput("old_state.ivec", ivec, 0, ivec.length);
	}
	traceOutput("ciphertext", ciphertext, start, Math.min(len, 32));
	traceOutput("baseKey", baseKey, 0, baseKey.length);
	traceOutput("Ke", Ke, 0, Ke.length);
	}

	// Decrypt [confounder \| plaintext ] (without checksum)

	// AES in JCE
	Cipher cipher = Cipher.getInstance("AES/CTS/NoPadding");
	SecretKeySpec secretKey = new SecretKeySpec(Ke, "AES");
	IvParameterSpec encIv = new IvParameterSpec(ivec, 0, ivec.length);
	cipher.init(Cipher.DECRYPT_MODE, secretKey, encIv);
	byte[] plaintext = cipher.doFinal(ciphertext, start, len-hashSize);

	if (debug) {
	traceOutput("AES PlainText", plaintext, 0,
	Math.min(plaintext.length, 32));
	}

	Ki = deriveKey(baseKey, usage, (byte) 0x55); // Integrity key
	if (debug) {
	traceOutput("Ki", Ki, 0, Ke.length);
	}

	// Verify checksum
	// H = HMAC(Ki, IV \| C)
	byte[] msg = Arrays.copyOf(ivec, ivec.length + len-hashSize);
	System.arraycopy(ciphertext, start, msg, ivec.length, len-hashSize);
	byte[] calculatedHmac = getHmac(Ki, msg);
	int hmacOffset = start + len - hashSize;
	if (debug) {
	traceOutput("calculated Hmac", calculatedHmac,
	0, calculatedHmac.length);
	traceOutput("message Hmac", ciphertext, hmacOffset, hashSize);
	}
	boolean cksumFailed = false;
	if (calculatedHmac.length >= hashSize) {
	for (int i = 0; i < hashSize; i++) {
	if (calculatedHmac[i] != ciphertext[hmacOffset+i]) {
	cksumFailed = true;
	if (debug) {
	System.err.println("Checksum failed !");
	}
	break;
	}
	}
	}
	if (cksumFailed) {
	throw new GeneralSecurityException("Checksum failed");
	}

	if (confounder_exists) {
	// Get rid of confounder
	// [ confounder \| plaintext ]
	byte[] output = new byte[plaintext.length - BLOCK_SIZE];
	System.arraycopy(plaintext, BLOCK_SIZE, output,
	0, output.length);
	return output;
	} else {
	return plaintext;
	}
	} finally {
	if (Ke != null) {
	Arrays.fill(Ke, 0, Ke.length, (byte) 0);
	}
	if (Ki != null) {
	Arrays.fill(Ki, 0, Ki.length, (byte) 0);
	}
	}
	}

	/*
	* Invoke the PKCS#5 PBKDF2 algorithm
	*/
	private static byte[] PBKDF2(char[] secret, byte[] salt,
	int count, int keyLength) throws GeneralSecurityException {

	PBEKeySpec keySpec = new PBEKeySpec(secret, salt, count, keyLength);
	SecretKeyFactory skf =
	SecretKeyFactory.getInstance(keyLength == 128 ?
	"PBKDF2WithHmacSHA256" : "PBKDF2WithHmacSHA384");
	SecretKey key = skf.generateSecret(keySpec);
	byte[] result = key.getEncoded();

	return result;
	}

	public static final int readBigEndian(byte[] data, int pos, int size) {
	int retVal = 0;
	int shifter = (size-1)*8;
	while (size > 0) {
	retVal += (data[pos] & 0xff) << shifter;
	shifter -= 8;
	pos++;
	size--;
	}
	return retVal;
	}

	}