public class PBKDF2Hash
{
private static final String PBKDF2_ALGORITHM = "PBKDF2WithHmacSHA1";
// The following constants may be changed without breaking existing hashes.
private static final int SALT_BYTE_SIZE = 24;
private static final int HASH_BYTE_SIZE = 24;
private static final int PBKDF2_ITERATIONS = 1000;
private static final int ITERATION_INDEX = 1;
private static final int SALT_INDEX = 2;
private static final int PBKDF2_INDEX = 3;
private static final Pattern COLON_PATTERN = Pattern.compile(":");
/**
* 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(final 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(final char[] password)
throws NoSuchAlgorithmException, InvalidKeySpecException
{
// Generate a random salt
final SecureRandom random = new SecureRandom();
final byte[] salt = new byte[SALT_BYTE_SIZE];
random.nextBytes(salt);
// Hash the password
final byte[] hash = pbkdf2(password, salt, PBKDF2_ITERATIONS, HASH_BYTE_SIZE);
// format iterations:salt:hash
return "sha1:" + PBKDF2_ITERATIONS + ':' + toBase64(salt) + ':' + toBase64(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(final String password, final 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(final char[] password, final CharSequence correctHash)
throws NoSuchAlgorithmException, InvalidKeySpecException
{
// Decode the hash into its parameters
final String[] params = COLON_PATTERN.split(correctHash);
final int iterations = Integer.parseInt(params[ITERATION_INDEX]);
final byte[] salt = fromBase64(params[SALT_INDEX]);
final byte[] hash = fromBase64(params[PBKDF2_INDEX]);
// Compute the hash of the provided password, using the same salt,
// iteration count, and hash length
final 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(final byte[] a, final 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(final char[] password, final byte[] salt, final int iterations, final int bytes)
throws NoSuchAlgorithmException, InvalidKeySpecException
{
final KeySpec spec = new PBEKeySpec(password, salt, iterations, bytes * 8);
final 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[] fromBase64(final String hex)
{
return DatatypeConverter.parseBase64Binary(hex);
}
/**
* 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 toBase64(final byte[] array)
{
return DatatypeConverter.printBase64Binary(array);
}
}
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