How to Verify User Passwords Without Decrypting Hashes Using PHP\'s `password_hash` Function?

Decryption of Password Hashes in PHP with Password_hash Function

Question:

You need to decrypt a password that is encrypted using the password_hash function. Assuming the hashed password is stored in a database, and you have a plaintext password entered by the user, how do you determine if they match without compromising security?

Answer:

Bcrypt is the hashing algorithm used by the password_hash function, and it is irreversible. Therefore, there is no direct way to decrypt hashed passwords.

Instead, to validate the user's password, follow these steps:

1. Retrieve the hashed password from the database using a SQL query that only selects the username. This ensures security by preventing SQL injection vulnerabilities.
2. Use the password_verify function to compare the user's plaintext password with the hashed password. It returns true if they match, indicating a valid login.

Example Code for Password Validation:

<code class="php">// Assume $hash is the hashed password from the database
if (password_verify($inputPassword, $hash)) {
    echo 'Password is valid!';
} else {
    echo 'Invalid password.';
}</code>

Important Note:

It's crucial to parameterize user input in SQL queries to prevent SQL injection attacks. Consult the Stack Overflow answer provided for guidance on this practice.

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