How to generate OTP Number with 6 digits

Question

What is an OTP number in a login authentication system? Is there any specific algorithm for generating OTP numbers using java (android). Or is an OTP something like random n

Answer 1

Java 8 introduced SplittableRandom in it's java.util package. You can use it's nextInt(int origin, int bound) to get a random number between the specified bound.

StringBuilder generatedOTP = new StringBuilder();
SplittableRandom splittableRandom = new SplittableRandom();

for (int i = 0; i < lengthOfOTP; i++) {

    int randomNumber = splittableRandom.nextInt(0, 9);
    generatedOTP.append(randomNumber);
}
return generatedOTP.toString();

But I will recommend to use SecureRandom class. It provides a cryptographically strong random number and available in the package java.security.

StringBuilder generatedOTP = new StringBuilder();
SecureRandom secureRandom = new SecureRandom();

try {

    secureRandom = SecureRandom.getInstance(secureRandom.getAlgorithm());

    for (int i = 0; i < lengthOfOTP; i++) {
        generatedOTP.append(secureRandom.nextInt(9));
    }
} catch (NoSuchAlgorithmException e) {
    e.printStackTrace();
}

return generatedOTP.toString();

You may get more info from Java 8- OTP Generator