OTP-Java

A small and easy-to-use one-time password generator for Java implementing RFC 4226 (HOTP) and RFC 6238 (TOTP).

Table of Contents

• Features
• Installation
• Usage
  • HOTP (Counter-based one-time passwords)
  • TOTP (Time-based one-time passwords)
  • Recovery codes

Features

The following features are supported:

1. Generation of secrets
2. Time-based one-time password (TOTP, RFC 6238) generation based on current time, specific time, OTPAuth URI and more for different HMAC algorithms.
3. HMAC-based one-time password (HOTP, RFC 4226) generation based on counter and OTPAuth URI.
4. Verification of one-time passwords
5. Generation of OTP Auth URI's

Installation

Maven

<dependency>
    <groupId>com.github.bastiaanjansen</groupId>
    <artifactId>otp-java</artifactId>
    <version>2.1.0</version>
</dependency>

Gradle

implementation 'com.github.bastiaanjansen:otp-java:2.1.0'

Scala SBT

libraryDependencies += "com.github.bastiaanjansen" % "otp-java" % "2.1.0"

Apache Ivy

<dependency org="com.github.bastiaanjansen" name="otp-java" rev="2.1.0" />

Or you can download the source from the GitHub releases page.

Usage

HOTP (Counter-based one-time passwords)

Initialization HOTP instance

To create a HOTPGenerator instance, use the HOTPGenerator.Builder class as follows:

String secret = "VV3KOX7UQJ4KYAKOHMZPPH3US4CJIMH6F3ZKNB5C2OOBQ6V2KIYHM27Q";
HOTPGenerator hotp = new HOTPGenerator.Builder(secret).build();

The above builder creates a HOTP instance with default values for passwordLength = 6 and algorithm = SHA1. Use the builder to change these defaults:

HOTPGenerator hotp = new HOTPGenerator.Builder(secret)
        .withPasswordLength(8)
        .withAlgorithm(HMACAlgorithm.SHA256)
        .build();

If you have a shared secret described in RFC-4226, you need to encode it first:

byte[] sharedSecret = getMySharedSecret();

byte[] secret = Base32.encode(sharedSecret);

When you don't already have a secret, you can let the library generate it:

// To generate a Base32-encoded secret with 160 bits
byte[] secret = SecretGenerator.generate();

// To generate a Base32-encoded secret with a custom amount of bits
byte[] secret = SecretGenerator.generate(512);

It is also possible to create a HOTP instance based on an OTPAuth URI. When algorithm or digits are not specified, the default values will be used.

URI uri = new URI("otpauth://hotp/issuer?secret=ABCDEFGHIJKLMNOP&algorithm=SHA1&digits=6&counter=8237");
HOTPGenerator hotp = HOTPGenerator.fromURI(uri);

Get information about the generator:

int passwordLength = hotp.getPasswordLength(); // 6
HMACAlgorithm algorithm = hotp.getAlgorithm(); // HMACAlgorithm.SHA1

Generation of HOTP code

After creating an instance of the HOTP class, a code can be generated by using the generate() method:

try {
    int counter = 5;
    String code = hotp.generate(counter);
    
    // To verify a token:
    boolean isValid = hotp.verify(code, counter);
    
    // Or verify with a delay window
    boolean isValid = hotp.verify(code, counter, 2);
} catch (IllegalStateException e) {
    // Handle error
}

TOTP (Time-based one-time passwords)

Initialization TOTP instance

TOTP can accept more paramaters: passwordLength, period, algorithm and secret. The default values are: passwordLength = 6, period = 30 and algorithm = SHA1.

// Generate a secret (or use your own secret)
byte[] secret = SecretGenerator.generate();

TOTPGenerator totp = new TOTPGenerator.Builder(secret)
        .withHOTPGenerator(builder -> {
            builder.withPasswordLength(6);
            builder.withAlgorithm(HMACAlgorithm.SHA1); // SHA256 and SHA512 are also supported
        })
        .withPeriod(Duration.ofSeconds(30))
        .build();

Or create a TOTP instance from an OTPAuth URI:

URI uri = new URI("otpauth://totp/issuer?secret=ABCDEFGHIJKLMNOP&algorithm=SHA1&digits=6&period=30");
TOTPGenerator totpGenerator = TOTPGenerator.fromURI(uri);

Get information about the generator:

int passwordLength = totpGenerator.getPasswordLength(); // 6
HMACAlgorithm algorithm = totpGenerator.getAlgorithm(); // HMACAlgorithm.SHA1
Duration period = totpGenerator.getPeriod(); // Duration.ofSeconds(30)

Generation of TOTP code

After creating an instance of the TOTP class, a code can be generated by using the now() method, similarly with the HOTP class:

try {
    String code = totpGenerator.now();
     
    // To verify a token:
    boolean isValid = totpGenerator.verify(code);
} catch (IllegalStateException e) {
    // Handle error
}

The above code will generate a time-based one-time password based on the current time. The API supports, besides the current time, the creation of codes based on timeSince1970 in seconds, Date, and Instant:

try {
    // Based on current time
    totpGenerator.now();
    
    // Based on specific date
    totpGenerator.at(new Date());
    
    // Based on specific local date
    totpGenerator.at(LocalDate.of(2023, 3, 2));
    
    // Based on seconds past 1970
    totpGenerator.at(9238346823);
    
    // Based on an instant
    totpGenerator.at(Instant.now());
} catch (IllegalStateException e) {
    // Handle error
}

Generation of OTPAuth URI's

To easily generate a OTPAuth URI for easy on-boarding, use the getURI() method for both HOTP and TOTP. Example for TOTP:

TOTPGenerator totpGenerator = new TOTPGenerator.Builder(secret).build();

URI uri = totpGenerator.getURI("issuer", "account"); // otpauth://totp/issuer:account?period=30&digits=6&secret=SECRET&algorithm=SHA1

Recovery Codes

Often, services provide "backup codes" or "recovery codes" which can be used when the user cannot access the 2FA device anymore. Often because 2FA device is a mobile phone, which can be lost or stolen.

Because recovery code generation is not part of the specifications of OTP, it is not possible to generate recovery codes with this library and should be implemented seperately.

Licence

OTP-Java is available under the MIT License. See the LICENCE for more info.