Password4j is a Java utility package for hashing and checking passwords with different Cryptographic hash function (CHFs).

Algorithms can be configured programmatically or through a property file in your classpath ^{see Configuration section}.

The configurations are mostly dependent on your environment. Password4j delivers a tool that can create a set of optimal parameters based on the system performance and the desired maximum computational time ^{see Performance section}.

The library fully supports BCrypt, SCrypt and PBKDF2 and can produce and handle cryptographic salt and pepper.

Installation

Password4j runs on Java 8, Java 9, Java 10 and Java 11 by any vendor. It is supported by Android API 26+ as well.

The artifacts are deployed to Maven Central.

Maven

Add the dependency of the latest version to your pom.xml:

<dependency>
    <groupId>com.password4j</groupId>
    <artifactId>password4j</artifactId>
    <version>1.3.2</version>
</dependency>

Gradle

Add to your build.gradle module dependencies:

repositories {
    mavenCentral()
}

dependencies {
    implementation 'com.password4j:password4j:1.3.2'
}

Scala SBT

Add to the managed dependencies of your build.sbt the latest version:

libraryDependencies += "com.password4j" % "password4j" % "1.3.2"

Usage

Password4j provides three main features.

Hash the password

Here it is the easiest way to hash a password with a CHF (BCrypt in this case)

Hash hash = Password.hash(password).withBCrypt();

Salt and pepper may be optionally added to the builder (PBKDF2 in this case):

// PBKDF2 with salt 12 bytes long (randomly generated).
Hash hash = Password.hash(password).addRandomSalt(12).withPBKDF2();

// PBKDF2 with a chosen salt.
Hash hash = Password.hash(password).addSalt(salt).withPBKDF2();

// PBKDF2 with chosen salt and pepper.
Hash hash = Password.hash(password).addSalt(salt).addPepper(pepper).withPBKDF2();

// Custom PBKDF2 (PBKDF2 with HMAC-SHA512, 64000 iterations and 512bit length).
Hash hash = Password.hash(password).with(PBKDF2Function.getInstance(Hmac.SHA512, 64000, 512));

The same structure can be adopted for the other CHFs, not just for PBKDF2.

Verify the hash

With the same ease you can verify an hash

boolean verified = Password.check(password, hash).withBCrypt();

Salt and pepper may be optionally added to the builder (PBKDF2 in this case):

// Verify with PBKDF2.
boolean verification = Password.check(password, hash).withPBKDF2();

// Verify with PBKDF2 and manually provided salt.
boolean verification = Password.check(password, hash).addSalt(salt).withPBKDF2();

// Verify with PBKDF2 and manually provided salt and pepper.
boolean verification = Password.check(password, hash).addSalt(salt).addPepper(pepper).withPBKDF2();

The same structure can be adopted for the other algorithms, not just for PBKDF2. Take in account that BCrypt and SCrypt store the salt inside the hash, so the addSalt() method is not needed.

Update the hash

When a configuration is not considered anymore secure you can refresh the hash like this:

HashUpdate update = Password.check(password, hash).update().withBCrypt();

if(update.isVerified())
{
    Hash newHash = update.getHash();
}

Or if you want to switch from a CHF to another one:

PBKDF2Function pbkdf2 = AlgorithmFinder.getPBKDF2Instance();
HashUpdate update = Password.check(password, hash).update().withSCrypt(pbkdf2);

if(update.isVerified())
{
    Hash newHash = update.getHash();
}

Security of Strings

Strings are immutable objects and they are stored in the String Pool, a location in the heap memory. Since you do not have control on the Garbage Collector, an attacker that has access to the memory could read the password just before you use it as input for Password4j. Even after this, the String may be still persisted in memory until the garbage collection occurs.

It is always recommended to use char[] instead of String ^{(where possible - If we're talking of a web application, most web containers will pass the password into the HttpServletRequest object in plaintext as String)}.

For this reason Password4j provides a SecureString class that alleviates this problem. The provided char[] is wrapped around SecureString and it is never converted into a String during the process.

You can erase the underlying char[] with clear() method.

SecureString secure = new SecureString(new char[]{...});

Passowrd.hash(secure).withBCrypt();
Password.check(secure, hash).withBCrypt();

secure.clear();
// At this point the underlying char[] = {\0, \0, \0, ...}

In addition to this, you may want to clean the original char[]. With the following code even the source is zeroed:

char[] password = {...}
SecureString secure = new SecureString(password, true);

// At this point password = {\0, \0, \0, ...}

The pepper can be expressed as SecureString as well.

Configuration

Password4j makes available a portable way to configure the library.

With the property file psw4j.properties put in your classpath, you can define the parameters of all the supported CHFs or just the CHF(s) you need. Alternatively you can specify a custom path with the system property -Dpsw4j.configuration

java -Dpsw4j.configuration=/my/path/to/some.properties ...

Here's a basic configuration (please do not use it in production, but instead start a benchmark session in your target environment^{see Performance section})

### PBKDF2
# with HMAC-SHA256
hash.pbkdf2.algorithm=SHA256
# 64000 iterations
hash.pbkdf2.iterations=64000
# derived key of 256bit 
hash.pbkdf2.length=256

### BCrypt
hash.bcrypt.minor=b
# logarithmic cost (cost = 2^12)
hash.bcrypt.rounds=12

### SCrypt
# N
hash.scrypt.workfactor=16384
# r
hash.scrypt.resources=16
# p
hash.scrypt.parallelization=1

Additionally you can define here your shared pepper

global.pepper=AlicePepper

and use it like this

// Hash
Password.hash("password").addPepper().withSCrypt();

// Verify
Password.check("password", "hash").addPepper().withSCrypt();

SecureRandom may be instantiated through SecureRandom.getInstanceStrong()

global.random.strong=true

but make sure that your JVM supports it and it points to a non-blocking source of entropy, otherwise you may experience huge performance drops^{see SecureRandom}.

Performance

^{This tool must be used in the target system because performances may vary on different environments.}

Password4j is delivered with a tool that helps the developers to choose the right parameters for a specific CHF.

The class SystemChecker can be used to find these optimal values.

Here's an example on how to configure PBKDF2:

Hmac algorithm = Hmac.SHA256;
int length = algorithm.bits();
long maxTimeInMilliseconds = 150;

int iterations  = SystemChecker.findIterationsForPBKDF2(maxTimeInMilliseconds, algorithm, length);

System.out.println("Iterations: " + iterations);

A similar approach can be used for BCrypt:

long maxTimeInMilliseconds = 150;

int rounds = SystemChecker.findRoundsForBCrypt(maxTimeInMilliseconds);

System.out.println("Rounds: " + rounds);

And SCrypt:

int r = 16;
int p = 1;
long maxTimeInMilliseconds = 150;

int N = SystemChecker.findWorkFactorForSCrypt(maxTimeInMilliseconds, r, p);
r = SystemChecker.findResourcesForSCrypt(maxTimeInMilliseconds, N, p);

System.out.println("N: " + N + ", r: " + r);

Contributing

Please read CONTRIBUTING.md for details on our code of conduct, and the process for submitting pull requests to us.

Versioning

We use SemVer for versioning.

For the versions available, see the tags on this repository.

Authors

• David Bertoldi - Initial work - firaja

See also the list of contributors who participated in this project.

License

This project is licensed under the Apache License 2.0 License - see the LICENSE file for details

Changelog

See the CHANGELOG.md file for a more detailed description of each release.