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tanszek:oktatas:techcomm:luhn_algortithm_to_protect_credit_card_numbers

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tanszek:oktatas:techcomm:luhn_algortithm_to_protect_credit_card_numbers [2024/11/05 16:44] – created kneheztanszek:oktatas:techcomm:luhn_algortithm_to_protect_credit_card_numbers [2024/11/12 12:06] (current) – [Steps of the Luhn Algorithm] knehez
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 1. **Reverse the order** of the card number's digits. 1. **Reverse the order** of the card number's digits.
 +
 2. **Double every second digit**, starting from the first digit (which is now the second digit of the reversed number). 2. **Double every second digit**, starting from the first digit (which is now the second digit of the reversed number).
 +
 3. If any doubled value is greater than 9, **subtract 9 from it** (alternatively, add the digits together; e.g., 12 becomes 1 + 2 = 3). 3. If any doubled value is greater than 9, **subtract 9 from it** (alternatively, add the digits together; e.g., 12 becomes 1 + 2 = 3).
 +
 4. **Sum all the digits** (including both doubled and undoubled digits). 4. **Sum all the digits** (including both doubled and undoubled digits).
 +
 5. **Check if the sum is divisible by 10**. If it is, the card number is valid. 5. **Check if the sum is divisible by 10**. If it is, the card number is valid.
  
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 1. Reverse it: **7646 3430 8841 9354** 1. Reverse it: **7646 3430 8841 9354**
 +
 2. Double every second digit: **7, 12, 4, 12, 6, 6, 3, 6, 8, 16, 4, 2, 9, 6, 5, 8** 2. Double every second digit: **7, 12, 4, 12, 6, 6, 3, 6, 8, 16, 4, 2, 9, 6, 5, 8**
 +
 3. For doubled values greater than 9 (12, 12, 16), add their digits: **7, 3, 4, 3, 6, 6, 3, 6, 8, 7, 4, 2, 9, 6, 5, 8** 3. For doubled values greater than 9 (12, 12, 16), add their digits: **7, 3, 4, 3, 6, 6, 3, 6, 8, 7, 4, 2, 9, 6, 5, 8**
 +
 4. Sum: **70** 4. Sum: **70**
 +
 5. Since **70 is divisible by 10**, the card number is **valid**. 5. Since **70 is divisible by 10**, the card number is **valid**.
  
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 </sxh> </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 === 
 + 
 +1. **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). 
 + 
 +2. **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. 
 + 
 +3. **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> 
tanszek/oktatas/techcomm/luhn_algortithm_to_protect_credit_card_numbers.1730825087.txt.gz · Last modified: 2024/11/05 16:44 by knehez