How Does PHP's `password_hash` Securely Handle Passwords and Verify Logins?

How to Use PHP's password_hash to Securely Hash and Verify Passwords

In an effort to enhance the security of your login script, you've encountered password_hash and are seeking clarification on its functionality. Here's a detailed breakdown to answer your questions:

Is Salt Generated by password_hash?

Yes, when using password_hash, a unique salt is automatically generated for each password. This is a cryptographically secure random value that is combined with the password before hashing. Salt prevents rainbow table attacks, making it more difficult to crack passwords.

Storing Salt Separately: A Misconception

Your suggestion to have separate salts in the file and database is based on a misconception. Storing salts is never recommended for security reasons. The point of using a salt is to make it difficult for attackers to determine the underlying hash function and password. Separating salts defeats that purpose.

The Correct Approach:

1. Hash the Password: Use password_hash to generate a salted hash from the user's password. Store the hash in the database, ensuring it's long enough (at least 60 characters).
2. Verify Login: When a user attempts to log in, compare the entered password with the hashed password in the database using password_verify. This ensures that the entered password matches the original password, preventing unauthorized access.

Example Code:

$password = $_POST['password'];
$hashed_password = password_hash($password, PASSWORD_DEFAULT);

// Store $hashed_password in the database

// For login verification:
if (password_verify($password, $hashed_password)) {
    // User provided the correct password
} else {
    // Password mismatch
}

Conclusion:

By understanding the proper use of password_hash, you can build secure login systems without needing to implement complex salt generation mechanisms. It generates salted hashes, prevents rainbow table attacks, and ensures the privacy and integrity of user passwords.

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