Understanding Differing Hash Values in Password_Hash Function

In developing secure authentication systems, developers often encounter the confusion of obtaining varying password hashes using the password_hash function. To clarify this behavior and ensure correct password verification, let's analyze the mechanics behind this function.

Password Salting: A Deliberate Feature

The password_hash function intentionally generates a unique salt for each password it hashes. Salting is a crucial security measure designed to prevent attackers from exploiting precomputed rainbow tables or guessing common hash values. With varying salts, each password becomes uniquely encrypted, significantly increasing the effort required to compromise the system.

Cost Parameter: Tailoring Security

To enhance the security of password hashing, the password_hash function allows developers to specify a cost parameter. This parameter controls the number of iterations used in the hashing algorithm, thereby increasing the computational effort required to break the hash. By default, the cost parameter is set to 10, which represents a reasonable balance between security and efficiency. To further increase security, developers can increase this value, as demonstrated in the following code:

$password = password_hash($password4, PASSWORD_DEFAULT, ['cost' => 15]);

Verification: Comparing Hashes

When verifying passwords, it's essential to ensure that the unencrypted password provided by the user is correctly hashed before being compared to the stored hash. This is done using the password_verify function:

if(password_verify($password4, $dbpassword))

In this code snippet, $password4 represents the user's entered password (which is not hashed), and $dbpassword represents the hashed password stored in your database. By comparing the two hashed values, the function returns true if the passwords match, allowing authentication to proceed.