How to validate CVV number using Regular Expression?

A three- or four-digit number is called the Card Verification Value, or CVV, that is found on the back of most of the credit cards and debit cards as well as on the front of American Express cards. It is also known as CVV2 and CSC (Card Security Code).

The CVV code is a security mechanism to ensure that the person making the purchase has a valid card. It was developed to aid in preventing unauthorised transactions. It is typically required when making online purchases over the phone or without a card on hand.

Method

The following methods are used to validate a CVV number using Regular Expression −

• For 3-digit CVV code

• For 4-digit CVV code

Method 1: For 3-digit CVV code

The majority of credit and debit cards have a security trait imprinted on their backsides exclusively. This specific feature is a three-digit number that goes by the name of the CVV or Card Verification Value code, which comes in handy to authenticate the credence of the card while shopping online or over the phone without having it present physically. Provided any given input complies with a confirmed CVV code configuration format, it can be identified via regular expressions.

A string of characters known as a regular expression designates a search pattern. A regular expression can be used to verify whether an input has three digits in the case of a CVV number.

Syntax

The syntax for validating a three-digit CVV code using Regular Expression is as follows −

^\d {3}$

Where d stands for any digit character, 3 represents the precise number of times the previous character (digit) should appear, and $ denotes the end of the string.

A string of precisely three numbers, which is the format for a three-digit CVV code, matches this regular expression pattern. It can be used to check user input for accuracy and make sure the CVV code is entered in the right format.

Algorithm

An algorithm to validate a 3-digit CVV code using Regular Expression −

Step 1 − Create a Regular Expression pattern that a 3-digit number matches. The correct pattern is "d3," where "d" stands for any digit and "3" designates that there must be precisely three of them.

Step 2 − Design a method that checks the CVV code. A boolean value indicating whether the string matches the CVV pattern should be returned by the function after receiving a string as input.

Step 3 − Utilise Python's re module inside the method to compile the Regular Expression pattern. An illustration would be "cvv_pattern = re.compile(r'd3')".

Step 4 − Check whether the input string matches the CVV pattern using the match () method of the compiled pattern. As an illustration, use "match = cvv_pattern.match(input_str)".

Step 5 − Return True if the match is successful (that is, the input string fits the CVV pattern). If not, return False.

Example 1

An illustration of how a regular expression can be used in C++ to automatically validate a 3-digit CVV code.

In this illustration, the sample CVV code is initially defined as a string variable. Then, using the syntax [0-9]3, we build a regular expression pattern that matches any run of three digits.

The regular expression pattern is compared against the CVV code using the std::regex_match() function. We print on the screen "Valid CVV code" if the CVV code matches the pattern else, we show "Invalid CVV code."

#include <iostream>
#include <regex>
#include <string>

int main() {
   std::string cvv = "123"; // Example CVV code
   std::regex cvv_regex("[0-9]{3}");

   if (std::regex_match(cvv, cvv_regex)) {
      std::cout << "Valid CVV code\n";
   } else {
      std::cout << "Invalid CVV code\n";
   }
   return 0;
}

Output

Valid CVV code

Method 2: For 4-digit CVV code

In the realm of credit and debit cards, the 4-digit CVV code serves as a variation of the Card Verification Value (CVV). While most card users only make use of three-digit CVV codes, American Express stands amongst the exception with their use of four-digit codes. By applying a regular expression, individuals can ensure that any correctly entered 4-digit CVV numbers are verified effectively.

Syntax

A syntax of a regular expression that can be used to validate a 4-digit CVV code −

^\d {4}$

This regular expression breaks down as follows −

• ^ - Start of string

• \d - Any digit (0-9)

• {4} - Exactly four times

• $ - End of string

This regular expression only identifies strings that have exactly four digits in total. The CVV code will be output as invalid if the user given values a CVV code that is not exactly four digits and contains any non-digit characters because the regular expression will not match.

Algorithm

A step-by-step algorithm for validating a 4-digit CVV code using a Regular Expression −

Step 1 − Establish a Regular Expression pattern that will match a four-digit number. The formula for the pattern is d4, which corresponds to any run of four numbers.

Step 2 − Obtain the user's CVV code.

Step 3 − To see if the CVV code matches the pattern, use the Regular Expression pattern. The For instance, you can compare the CVV code to the pattern in Python using the re.match() function.

Step 4 − The CVV code is a legitimate 4-digit CVV code if it matches the pattern. You can carry out the transaction now.

Step 5 − If your CVV code do not resemble the pattern, then it is not a valid 4-digit CVV code. One can print the error message to the user and print in the screen enter a valid CVV code.

Example 2

Here is a C++ example of how to validate a four-digit CVV code using regular expressions without user input −

In this example, we construct a Regular Expression pattern that matches 4-digit numbers using the std::regex class. The cvv_regex variable holds the pattern.

The std regex_match function is used to find whether the cvv string matches the cvv_regex pattern. The CVV code is concerned if the string conforms to the pattern; otherwise, it is confirmed as invalid.

#include <iostream>
#include <regex>

int main() {
   std::string cvv = "124"; // The CVV code to validate

   // Regular Expression to match 4-digit numbers
   std::regex cvv_regex("\b\d{4}\b");

   if (std::regex_match(cvv, cvv_regex)) {
      std::cout << "Valid CVV code." << std::endl;
   } else {
      std::cout << "Invalid CVV code." << std::endl;
   }
   return 0;
}

Output

Invalid CVV code.

Conclusion

Using a regular expression to validate a CVV number can help to guarantee that the input is in the right format and satisfies the criteria for a valid CVV. A CVV pattern is typically represented by the regular expression "bd3,4b", which matches a string of three or four digits enclosed in word boundaries. The security of credit and debit card transactions can be enhanced by developers by checking the CVV input against this regular expression.