Differences

This shows you the differences between two versions of the page.

--- tanszek:oktatas:techcomm:luhn_algortithm_to_protect_credit_card_numbers [2024/11/05 16:45] – knehez
+++ tanszek:oktatas:techcomm:luhn_algortithm_to_protect_credit_card_numbers [2024/11/12 12:06] (current) – [Steps of the Luhn Algorithm] knehez
@@ Line 42: / Line 42: @@
 </sxh>
-This code will output whether the credit card number is valid or invalid based on the Luhn algorithm.
+Here is a C implementation of the algorithm:
+<sxh c>
+#include <stdio.h>
+#include <string.h>
+#include <ctype.h>
+// Function to validate a Visa card number using the Luhn Algorithm
+int isValidVisaCard(const char* cardNumber) {
+    int length = strlen(cardNumber);
+    int sum = 0;
+    int isSecond = 0;
+    // Traverse the card number in reverse
+    for (int i = length - 1; i >= 0; i--) {
+        int digit = cardNumber[i] - '0';
+        if (isSecond) {
+            // Double every second digit
+            digit *= 2;
+            if (digit > 9) {
+                // Subtract 9 if the doubled value is greater than 9
+                digit -= 9;
+            }
+        }
+        // Add digit to the sum
+        sum += digit;
+        // Toggle the isSecond flag
+        isSecond = !isSecond;
+    }
+    // If the sum is divisible by 10, the card number is valid
+    return (sum % 10 == 0);
+}
+int main() {
+    char cardNumber[20];
+    printf("Enter the Visa card number: ");
+    scanf("%19s", cardNumber);
+    if (isValidVisaCard(cardNumber)) {
+        printf("The card number is valid.\n");
+    } else {
+        printf("The card number is invalid.\n");
+    }
+    return 0;
+}
+</sxh>
+Based on the Luhn algorithm, this code will output whether the credit card number is valid or invalid.
+Generating a valid credit card number involves adhering to the structure and validation checks used by credit card companies, primarily the Luhn algorithm. Here’s how to generate a valid credit card number (without real-world use, as actual issuance requires official channels).
+=== Steps to Generate a Valid Credit Card Number ===
+. **Choose a Bank Identification Number (BIN)**: The first 6 digits of a credit card (the BIN) identify the issuing bank. For example:
+   - VISA typically starts with 4.
+   - MasterCard numbers often start with 51-55.
+   For this example, we’ll use a generic BIN: `4539 14` (representing a VISA card).
+. **Generate Remaining Digits Except the Checksum**: After the BIN, generate random digits for the rest of the card number, leaving the last digit blank for now. VISA and MasterCard usually have 16 digits, so we’ll generate 9 more digits.
+. **Calculate the Checksum with the Luhn Algorithm**:
+   - Apply the Luhn algorithm to calculate the checksum digit (the last digit), which will make the number valid.
+=== Example Code to Generate a Valid Card Number ===
+Here’s a Python code that generates a valid credit card number:
+<sxh python>
+import random
+def generate_credit_card():
+    # Start with a sample BIN (6 digits)
+    bin_number = [4, 5, 3, 9, 1, 4]  # Example BIN for VISA
+    # Generate the next 9 random digits
+    card_number = bin_number + [random.randint(0, 9) for _ in range(9)]
+    # Calculate the Luhn checksum for the first 15 digits
+    def luhn_checksum(card):
+        digits = card[::-1]
+        checksum = sum(digits[0::2]) + sum(sum(divmod(2 * d, 10)) for d in digits[1::2])
+        return checksum % 10
+    # Calculate the last digit to make the number valid
+    check_digit = (10 - luhn_checksum(card_number)) % 10
+    card_number.append(check_digit)
+    return ''.join(map(str, card_number))
+# Generate a valid credit card number
+print(generate_credit_card())
+</sxh>