To address the issue of fake export licenses, we need a robust validation system that checks both the format and authenticity of license numbers. Below is a Python implementation that validates export licenses against predefined criteria and a database of known fake licenses.

Solution Code

import re
FAKE_LICENSES = {
    "ABC1234567", "XYZ9876543", "DEF4567890"
}
def validate_export_license(license_number):
    """
    Validates an export license number based on format and authenticity.
    Args:
        license_number (str): The license number to validate.
    Returns:
        bool: True if valid, False otherwise.
    """
    # Check length
    if len(license_number) != 10:
        return False
    # Check format: 3 uppercase letters followed by 7 digits
    if not re.fullmatch(r'^[A-Z]{3}\d{7}$', license_number):
        return False
    # Check against fake licenses
    if license_number in FAKE_LICENSES:
        return False
    return True
# Example usage
if __name__ == "__main__":
    test_licenses = [
        "ABC1234567",  # Fake (in FAKE_LICENSES)
        "XYZ9876543",  # Fake (in FAKE_LICENSES)
        "DEF4567890",  # Fake (in FAKE_LICENSES)
        "LMN1234567",  # Valid (correct format, not fake)
        "abc1234567",  # Invalid (lowercase letters)
        "AB1234567",   # Invalid (too short)
        "AB12345678",  # Invalid (too long)
        "AB!234567",   # Invalid (contains non-alphanumeric)
    ]
    for license_num in test_licenses:
        is_valid = validate_export_license(license_num)
        print(f"License {license_num}: {'Valid' if is_valid else 'Invalid'}")

Explanation

1. Format Validation:

   • The license number must be exactly 10 characters long.
   • The first 3 characters must be uppercase letters (A-Z).
   • The remaining 7 characters must be digits (0-9).
   • This is enforced using a regular expression: ^[A-Z]{3}\d{7}$.

2. Fake License Check:

   • A predefined set FAKE_LICENSES contains known invalid license numbers.
   • If the input license matches any entry in this set, it is rejected.

3. Example Usage:

   The test cases demonstrate valid and invalid scenarios, including correct format, incorrect format, and known fake licenses.

Output

License ABC1234567: Invalid
License XYZ9876543: Invalid
License DEF4567890: Invalid
License LMN1234567: Valid
License abc1234567: Invalid
License AB1234567: Invalid
License AB12345678: Invalid
License AB!234567: Invalid

Key Points

• Security: Combines structural checks with a database of known fakes to prevent bypassing via format manipulation.
• Efficiency: Regular expressions ensure fast format validation, while set lookups provide O(1) time complexity for fake license checks.
• Extensibility: The FAKE_LICENSES set can be updated dynamically as new fake licenses are identified.

This solution effectively filters out fake export licenses by leveraging strict format rules and a blacklist of known fraudulent entries.