kotp

kotp is a Kotlin/JVM library for generating and verifying One-Time Password (OTP) codes, suitable for 2FA (Two-Factor Authentication) implementations.

Features

• HMAC-based OTP (HOTP): Generate and verify OTP codes based on a counter.
• Time-based OTP (TOTP): Generate and verify OTP codes based on time.
• Configurable: Define code length, time step and hashing algorithm
• Lightweight: Minimal dependencies and easy integration

Installation

Add the library to your project by including the following dependency:

Gradle (Kotlin DSL)

dependencies {
    implementation("dev.vicart:kotp:<version>")
}

Maven

<dependency>
    <groupId>dev.vicart</groupId>
    <artifactId>kotp</artifactId>
    <version>...</version>
</dependency>

Usage

TOTP (Time-based OTP)

Generation

val totpGenerator = TOTPGenerator()
val code = totpGenerator.generateCode("base32-encoded key")

Verification

val totpVerifier = TOTPVerifier()
val verified = totpVerifier.verify("base32-encoded key", "OTP code")

Note: kotp automatically checks for previous and next time step on verification for error detection

HOTP (HMAC-based OTP)

Generation

val hotpGenerator = HOTPGenerator()
val code = hotpGenerator.generateCode("base32-encoded key", 0)

Verification

val hotpVerifier = HOTPVerifier()
val verified = hotpVerifier.verify("base32-encoded key", "OTP code", 0)

Configuration

The library provides various options for customization:

• codeLength: Number of digits in the OTP (default: 6)
• period: Duration (in seconds) for which a TOTP is valid (Default: 30 seconds)
• algorithm: Hashing algorithm for OTP generation (Default: SHA1)