Initialize Generator

Documentation for creating an instance of the HMAC-Based One-Time Password Generator.

Create Instance

You can create an instance of the HotpGenerator in the following way:

val hotpGenerator = HotpGenerator()

Spring Boot

Instead of creating a new instance of a generator each time a token is checked, it is also possible to create a bean within Spring. This allows to configure the generator once and this configuration is maintained each time the bean is injected into a component.

@Bean
fun hotpGenerator(): HotpGenerator {
    val generator = HotpGenerator()
    generator.codeLength = 6
    generator.algorithm = HashAlgorithm.SHA1
    return generator
}

This bean can then be injected in the constructor of any class marked with @Component (@Service, ...).

@Component
class CustomComponent(private val hotpGenerator: HotpGenerator) {
    //...
}

Customize properties

It is possible to customize the properties of the generator, either by setters or applying them in the constructor.

Algorithm

The algorithm specifies the Hashing algorithm used to generate the 2-factor codes.

Could break logic

Most authenticator apps, such as those from Microsoft or Google, use SHA1 (although it is no longer considered secure). If you change the algorithm, the authentication app must also support it, or it cannot be used.

Code length

The code length specifies how long a generated code will be. If the code length is changed, it is necessary that the user's authenticator app supports this as well.

Could break logic

Most authenticator apps, such as those from Microsoft or Google, use a length of 6 digits. If you change this number, they are no longer usable. However, remember that that they are widely used before you drop support for them.