Algorithm Checksum Error Checking Data Consistency

How to Generate a Verification Code that Ensures User Input Accuracy

In today’s digital landscape, the need for secure verification methods is more prevalent than ever. Whether you’re working on an application or a service requiring user authentication, it’s crucial to establish a reliable method for users to validate their identities. One common approach is to generate a verification number that users must enter using their phone keypad.

The Problem

Generating a verification number should not only be random but must also meet certain requirements:

The code should be difficult to type correctly by accident or through typos.
Incorrect entries, like transposed digits or wrong digits, should ideally yield invalid codes.
The number of possible combinations should be reasonable (around 1 million).
The verification code must be short and easily typeable to minimize user errors.

With these criteria in mind, how do we efficiently generate such a numerical verification code?

The Solution

After examining several potential algorithms, the ISO 7064 Mod 97,10 formula emerged as a strong candidate. This algorithm is renowned for its reliability, having been employed to validate International Bank Account Numbers (IBANs). Here’s a detailed breakdown of how this algorithm works to generate and validate a verification code.

Step-by-Step Breakdown of the Algorithm

Choose a Base Number:
- Example base number: 123456

Calculate the Checksum:

Use the following formula to generate a two-digit checksum:
```
checksum = mod(98 - mod(number * 100, 97), 97)
```

For our example:

checksum = mod(98 - mod(123456 * 100, 97), 97) => checksum = 76

Combine the Base Number and Checksum:
- Concatenate the original number with the generated checksum to form the final verification code:
```
verification code = base number + checksum
```
- Resulting in: 12345676
Validation of the Code:
- To validate if a user-entered code is correct, use this formula:
```
valid if mod(code, 97) == 1
```

Testing the Algorithm

To illustrate the effectiveness of this method, let’s run a few tests with the generated verification code:

Valid Code Example:
```
test: mod(12345676, 97) = 1 => GOOD
```

Invalid Code Examples:

test: mod(21345676, 97) = 50 => BAD!
test: mod(12345678, 97) = 10 => BAD!

As seen in the examples, the algorithm successfully detects both valid and invalid numbers with a high degree of accuracy.

Alternative Options

While the ISO 7064 Mod 97,10 provides robust error detection, another intriguing option is the Verhoeff algorithm. This algorithm has the advantage of using a single verification digit but is noted for its complexity in implementation compared to the simpler ISO formula.

Conclusion

Incorporating a strong verification code algorithm can significantly enhance the security and user experience of any application requiring user input validation. The ISO 7064 Mod 97,10 algorithm stands out for its simplicity and effectiveness, making it a top choice for developers looking to create a numeric code for user verification.

By implementing this method into your application, you help ensure that the verification process is both secure and user-friendly, reducing potential input errors while maintaining data integrity.