com.peterphi.std.crypto

Class BCrypt

java.lang.Object

com.peterphi.std.crypto.BCrypt

public class BCrypt
extends Object

BCrypt implements OpenBSD-style Blowfish password hashing using the scheme described in "A Future-Adaptable Password Scheme" by Niels Provos and David Mazieres.

This password hashing system tries to thwart off-line password cracking using a computationally-intensive hashing algorithm, based on Bruce Schneier's Blowfish cipher. The work factor of the algorithm is parameterised, so it can be increased as computers get faster.

Usage is really simple. To hash a password for the first time, call the hashpw method with a random salt, like this:

String pw_hash = BCrypt.hashpw(plain_password, BCrypt.gensalt());


To check whether a plaintext password matches one that has been hashed previously, use the checkpw method:

if (BCrypt.checkpw(candidate_password, stored_hash))
System.out.println("It matches");
else
System.out.println("It does not match");


The gensalt() method takes an optional parameter (log_rounds) that determines the computational complexity of the hashing:

String strong_salt = BCrypt.gensalt(10)
String stronger_salt = BCrypt.gensalt(12)


The amount of work increases exponentially (2**log_rounds), so each increment is twice as much work. The default log_rounds is 10, and the valid range is 4 to 31.

Version:

0.3

Author:

Damien Miller

Constructor Summary

Constructors

Constructor and Description
BCrypt()

Method Summary

Modifier and Type	Method and Description
static boolean	checkpw(String plaintext, String hashed) Check that a plaintext password matches a previously hashed one
static String	gensalt() Generate a salt for use with the BCrypt.hashpw() method, selecting a reasonable default for the number of hashing rounds to apply
static String	gensalt(int log_rounds) Generate a salt for use with the BCrypt.hashpw() method
static String	gensalt(int log_rounds, SecureRandom random) Generate a salt for use with the BCrypt.hashpw() method
static String	hashpw(String password, String salt) Hash a password using the OpenBSD bcrypt scheme

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

BCrypt

public BCrypt()

Method Detail

hashpw

public static String hashpw(String password,
                            String salt)

Hash a password using the OpenBSD bcrypt scheme

Parameters:

password - the password to hash

salt - the salt to hash with (perhaps generated using BCrypt.gensalt)

Returns:

the hashed password

gensalt

public static String gensalt(int log_rounds,
                             SecureRandom random)

Generate a salt for use with the BCrypt.hashpw() method

Parameters:

log_rounds - the log2 of the number of rounds of hashing to apply - the work factor therefore increases as 2**log_rounds.

random - an instance of SecureRandom to use

Returns:

an encoded salt value

gensalt

public static String gensalt(int log_rounds)

Generate a salt for use with the BCrypt.hashpw() method

Parameters:

log_rounds - the log2 of the number of rounds of hashing to apply - the work factor therefore increases as 2**log_rounds.

Returns:

an encoded salt value

gensalt

public static String gensalt()

Generate a salt for use with the BCrypt.hashpw() method, selecting a reasonable default for the number of hashing rounds to apply

Returns:

an encoded salt value

checkpw

public static boolean checkpw(String plaintext,
                              String hashed)

Check that a plaintext password matches a previously hashed one

Parameters:

plaintext - the plaintext password to verify

hashed - the previously-hashed password

Returns:

true if the passwords match, false otherwise