Are there specific best practices or guidelines to follow when using regular expressions in PHP for cryptography or other sensitive data manipulation?

When using regular expressions in PHP for cryptography or other sensitive data manipulation, it is important to ensure that the regular expressions are secure and do not inadvertently expose the data to potential vulnerabilities. One best practice is to use predefined character classes or escape special characters to prevent injection attacks. Additionally, it is recommended to validate user input before applying regular expressions to avoid unexpected behavior.

// Example of using predefined character classes and validating user input
$user_input = $_POST['password'];

// Validate user input
if (preg_match('/^[\w\d]{8,}$/', $user_input)) {
    // Input meets criteria, proceed with regular expression manipulation
    // For example, hashing the password
    $hashed_password = password_hash($user_input, PASSWORD_DEFAULT);
} else {
    // Input does not meet criteria, handle error
    echo "Password must be at least 8 characters long and contain only letters and numbers.";
}