Many people believe it is impossible to correctly guess the 16 digits used to top up your sim card. People claim that a complex algorithm is used to generate those numbers, making guessing nearly impossible.

However, in my opinion, while knowing the algorithm employed will help you speed up your process, you don’t need to know it to crack the numbers.

With 16 digits on a top-up voucher, how many possible outcomes are there? So I tried generating 100 billion, which took about 4 hours, and I can assure you that I was nowhere near generating all possible numbers.

Maybe I needed to be more efficient; can I collect a handful of previously used vouchers and try to figure out any possible patterns? That makes sense considering.

How are vouchers generated?

The prepaid recharge pins or voucher activation codes are generated and stored in a server called Voucher Server. A telecom network mainly consists of Core Network Elements ( BTS, MSC, HLR, etc.) and Intelligence Network( IN). The core network’s function is mainly radio connectivity and switching whereas IN network’s function is that of call charging, recharge handling, billing, etc

The administrator will enter the Transaction Amount, Expiry, Serial Number Range, Agent Details, and other information into the Voucher Server, and an algorithm on the system will generate the voucher codes. These codes are usually encrypted.

It may look like any random number generator can be used but taking such risk is not possible so they will use certain algorithms That yield numbers with a certain minimum Hamming distance.

    private List<Long> generateRandomLoop(long limit) {
        List<Long> random= new ArrayList<>();
        for (int i = 0; i < limit; i++) {
            random.add(ThreadLocalRandom.current().nextLong(smallest, biggest + 1));
        }
        return random;
    }

When vouchers are generated, they are in the “Generated” or “Created” state. These pins cannot be recharged unless they are in the “AVAILABLE” state. As a result, a state change is performed on these vouchers as required (usually before printing them) to make them “AVAILABLE.” After that, the vouchers are ready to use.

Finally, when the user recharges the account, the voucher state is changed to “USED,” and it can no longer be used to refill the account.

Conclusion

Although artificial intelligence can be used to predict possible voucher numbers, you may end up predicting numbers from a batch that has already expired or a batch that is not yet in use. Furthermore, most telcos will limit the number of times you can attempt to load airtime.

Only when the distributor acknowledges the receipts are vouchers activated.