PBKDF2加密的实现
PBKDF2(Password-Based Key Derivation Function)。
通过哈希算法进行加密。由于哈希算法是单向的，能够将不论什么大小的数据转化为定长的“指纹”，并且无法被反向计算。
另外，即使数据源仅仅修改了一丁点。哈希的结果也会全然不同。
这种特性使得它很适合用于保存password。由于我们须要加密后的password无法被解密，同一时候也能保证正确校验每一个用户的password。可是哈希加密能够通过字典攻击和暴力攻击破解。
password加盐。盐是一个加入到用户的password哈希过程中的一段随机序列。
这个机制可以防止通过预先计算结果的彩虹表破解。每一个用户都有自己的盐，这种结果就是即使用户的password同样。通过加盐后哈希值也将不同。
为了校验password是否正确，我们须要储存盐值。通常和password哈希值一起存放在账户数据库中。或者直接存为哈希字符串的一部分。
package com.founder.mrp.util; /* * Password Hashing With PBKDF2 (http://crackstation.net/hashing-security.htm). * Copyright (c) 2013, Taylor Hornby * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions are met: * * 1. Redistributions of source code must retain the above copyright notice, * this list of conditions and the following disclaimer. * * 2. Redistributions in binary form must reproduce the above copyright notice, * this list of conditions and the following disclaimer in the documentation * and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE * POSSIBILITY OF SUCH DAMAGE. */ import java.math.BigInteger; import java.security.NoSuchAlgorithmException; import java.security.SecureRandom; import java.security.spec.InvalidKeySpecException; import javax.crypto.SecretKeyFactory; import javax.crypto.spec.PBEKeySpec; /* * PBKDF2 salted password hashing. * Author: havoc AT defuse.ca * www: http://crackstation.net/hashing-security.htm */ public class PasswordHash { public static final String PBKDF2_ALGORITHM = "PBKDF2WithHmacSHA1"; // The following constants may be changed without breaking existing hashes. public static final int SALT_BYTE_SIZE = 24; public static final int HASH_BYTE_SIZE = 24; public static final int PBKDF2_ITERATIONS = 1000; public static final int ITERATION_INDEX = 0; public static final int SALT_INDEX = 1; public static final int PBKDF2_INDEX = 2; /** * Returns a salted PBKDF2 hash of the password. * * @param password the password to hash * @return a salted PBKDF2 hash of the password */ public static String createHash(String password) throws NoSuchAlgorithmException, InvalidKeySpecException { return createHash(password.toCharArray()); } /** * Returns a salted PBKDF2 hash of the password. * * @param password the password to hash * @return a salted PBKDF2 hash of the password */ public static String createHash(char[] password) throws NoSuchAlgorithmException, InvalidKeySpecException { // Generate a random salt SecureRandom random = new SecureRandom(); byte[] salt = new byte[SALT_BYTE_SIZE]; random.nextBytes(salt); // Hash the password byte[] hash = pbkdf2(password, salt, PBKDF2_ITERATIONS, HASH_BYTE_SIZE); // format iterations:salt:hash return PBKDF2_ITERATIONS + ":" + toHex(salt) + ":" + toHex(hash); } /** * Validates a password using a hash. * * @param password the password to check * @param correctHash the hash of the valid password * @return true if the password is correct, false if not */ public static boolean validatePassword(String password, String correctHash) throws NoSuchAlgorithmException, InvalidKeySpecException { return validatePassword(password.toCharArray(), correctHash); } /** * Validates a password using a hash. * * @param password the password to check * @param correctHash the hash of the valid password * @return true if the password is correct, false if not */ public static boolean validatePassword(char[] password, String correctHash) throws NoSuchAlgorithmException, InvalidKeySpecException { // Decode the hash into its parameters String[] params = correctHash.split(":"); int iterations = Integer.parseInt(params[ITERATION_INDEX]); byte[] salt = fromHex(params[SALT_INDEX]); byte[] hash = fromHex(params[PBKDF2_INDEX]); // Compute the hash of the provided password, using the same salt, // iteration count, and hash length byte[] testHash = pbkdf2(password, salt, iterations, hash.length); // Compare the hashes in constant time. The password is correct if // both hashes match. return slowEquals(hash, testHash); } /** * Compares two byte arrays in length-constant time. This comparison method * is used so that password hashes cannot be extracted from an on-line * system using a timing attack and then attacked off-line. * * @param a the first byte array * @param b the second byte array * @return true if both byte arrays are the same, false if not */ private static boolean slowEquals(byte[] a, byte[] b) { int diff = a.length ^ b.length; for(int i = 0; i < a.length && i < b.length; i++) diff |= a[i] ^ b[i]; return diff == 0; } /** * Computes the PBKDF2 hash of a password. * * @param password the password to hash. * @param salt the salt * @param iterations the iteration count (slowness factor) * @param bytes the length of the hash to compute in bytes * @return the PBDKF2 hash of the password */ private static byte[] pbkdf2(char[] password, byte[] salt, int iterations, int bytes) throws NoSuchAlgorithmException, InvalidKeySpecException { PBEKeySpec spec = new PBEKeySpec(password, salt, iterations, bytes * 8); SecretKeyFactory skf = SecretKeyFactory.getInstance(PBKDF2_ALGORITHM); return skf.generateSecret(spec).getEncoded(); } /** * Converts a string of hexadecimal characters into a byte array. * * @param hex the hex string * @return the hex string decoded into a byte array */ private static byte[] fromHex(String hex) { byte[] binary = new byte[hex.length() / 2]; for(int i = 0; i < binary.length; i++) { binary[i] = (byte)Integer.parseInt(hex.substring(2*i, 2*i+2), 16); } return binary; } /** * Converts a byte array into a hexadecimal string. * * @param array the byte array to convert * @return a length*2 character string encoding the byte array */ private static String toHex(byte[] array) { BigInteger bi = new BigInteger(1, array); String hex = bi.toString(16); int paddingLength = (array.length * 2) - hex.length(); if(paddingLength > 0) return String.format("%0" + paddingLength + "d", 0) + hex; else return hex; } /** * Tests the basic functionality of the PasswordHash class * * @param args ignored */ public static void main(String[] args) { try { // Print out 10 hashes for(int i = 0; i < 10; i++) System.out.println(PasswordHash.createHash("123")); // Test password validation boolean failure = false; System.out.println("Running tests..."); for(int i = 0; i < 100; i++) { String password = ""+i; String hash = createHash(password); String secondHash = createHash(password); if(hash.equals(secondHash)) { System.out.println("FAILURE: TWO HASHES ARE EQUAL!"); failure = true; } String wrongPassword = ""+(i+1); if(validatePassword(wrongPassword, hash)) { System.out.println("FAILURE: WRONG PASSWORD ACCEPTED!"); failure = true; } if(!validatePassword(password, hash)) { System.out.println("FAILURE: GOOD PASSWORD NOT ACCEPTED!"); failure = true; } } if(failure) System.out.println("TESTS FAILED!"); else System.out.println("TESTS PASSED!"); } catch(Exception ex) { System.out.println("ERROR: " + ex); } } }
