password_verify()

password_verify() is a PHP function used to verify that a provided password matches a previously hashed password. It's a crucial component in securely implementing user authentication systems.

When a user's password is hashed and stored (typically during registration or password change processes), password_verify() allows you to compare the entered password during login with the stored hash.

The function takes two parameters: the plain-text password provided by the user and the hashed password stored in the database. It hashes the provided password using the same algorithm, salt, and cost factor that were used to create the original hash and then checks if this newly generated hash matches the stored one.

The function automatically identifies the hashing algorithm and salt used in the stored hash (as this information is part of the hash format generated by password_verify(), so there's no need for additional configuration.

An example of using it may be:

// User-provided password
$password = 'user_password';

// Hashed password retrieved from the database
$hashedPassword = '$2y$10$eCR3...'; // A hashed password

// Verifying the password
if (password_verify($password, $hashedPassword)) {
    echo 'Password is valid!';
} else {
    echo 'Invalid password.';
}

password_verify() is crucial for securely checking user passwords. Storing passwords in plain text or even in a poorly hashed format can be a significant security risk. password_verify() works in tandem with password_hash() to ensure that passwords are stored and verified securely.

The function is designed to be timing-attack safe, meaning that it takes the same amount of time to process regardless of how much of the input matches the stored hash. This prevents attackers from using timing information to guess the password.

It abstracts the complexities of secure password verification, making it easier for developers to follow best practices without having to be experts in cryptographic functions.