主要用于明文密码加密字符串存入数据库。由棱镜门思考。目前大部分企业中都是明文密码。一旦被攻破。危害非常大。现在主流加密技术是MD5加密。不过MD5的存在小概率碰撞(根据密码学的定义，如果内容不同的明文，通过散列算法得出的结果（密码学称为信息摘要）相同，就称为发生了“碰撞”。).如何生成md5碰撞的算法论文http://www.infosec.sdu.edu.cn/paper/md5-attack.pdf。一些黑客破获密码的方法是一种被称为“跑字典”的方法。有两种方法得到字典，一种是日常搜集的用做密码的字符串表，另一种是用排列组合方法生成的，先用MD5程序计算出这些字典项的MD5值，然后再用目标的MD5值在这个字典中检索。即使假设密码的最大长度为8，同时密码只能是字母和数字，共26+26+10=62个字符，排列组合出的字典的项数则是P(62,1)+P (62,2)….+P(62,8)，那也已经是一个很天文的数字了，存储这个字典就需要TB级的磁盘组，而且这种方法还有一个前提，就是能获得目标账户的 密码MD5值的情况下才可以。当如果用户的密码是弱密码的就很危险了。
PBKDF2WithHmacSHA1算法比MD5算法更安全。它可以同样密码在不同时间生成不同加密Hash。跑字典将无效。下面是算法Demo。
package hashpassword;
import java.security.SecureRandom;
import javax.crypto.spec.PBEKeySpec;
import javax.crypto.SecretKeyFactory;
import java.math.BigInteger;
import java.security.NoSuchAlgorithmException;
import java.security.spec.InvalidKeySpecException; /*
* 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 = 10; public static final int ITERATION_INDEX = 0;
public static final int SALT_INDEX = 1;
public static final int PBKDF2_INDEX = 2; public static String createHash(String password)
throws NoSuchAlgorithmException, InvalidKeySpecException
{
return createHash(password.toCharArray());
} /**
* Returns a salted PBKDF2 hash of the password.
* 返回一个加盐后的PBKDF2哈希密码
* @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 随即盐序列
SecureRandom random = new SecureRandom();
byte[] salt = new byte[SALT_BYTE_SIZE];
random.nextBytes(salt); // Hash the password 生成哈希密码
byte[] hash = pbkdf2(password, salt, PBKDF2_ITERATIONS, HASH_BYTE_SIZE);
// format iterations:salt:hash 格式化 迭代次数：盐：哈希
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.
* 计算PBKDF2哈希密码
* @param password the password to hash. 需要加密的明文密码
* @param salt the salt 盐增加调味 增加密码破解难度
* @param iterations the iteration count (slowness factor) 迭代次数
* @param bytes the length of the hash to compute in bytes 计算密码后的 哈希长度
* @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("p\r\nassw0Rd!")); // 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);
}
} }
https://crackstation.net/hashing-security.htm