PHP openssl_cipher_key_length() Function

The openssl_cipher_key_length() function is an inbuilt function in PHP that is used to retrieve the key length required for a given cipher algorithm.

Syntax:

openssl_cipher_key_length(string $cipher_algo): int|false

Parameters: This function accepts only one parameter which is described below.

• $cipher_algo: This is a string representing the cipher algorithm.

Return Values: The function returns an integer representing the length in bytes of the key required for the given cipher algorithm, or “false” on failure. 

Example 1: The following program demonstrates the openssl_cipher_key_length() function.

PHP

<?php
$cipher = "bf-cbc";
$key_len = openssl_cipher_key_length($cipher);
echo "Key length for {$cipher}: {$key_len}\n";
?>

Output:

Key length for bf-cbc: 16 

Example 2: The following program demonstrates the openssl_cipher_key_length() function.

PHP

<?php
$cipher = "AES-256-CBC";
$key_length = 24;

if ($key_length === openssl_cipher_key_length($cipher)) {
    echo "The key length is valid for $cipher.";
} else {
    echo "The key length is not valid for $cipher.";
}
?>

Output:

The key length is not valid for AES-256-CBC. 

Reference: https://www.php.net/manual/en/function.openssl-cipher-key-length.php