How can the mcrypt functions in PHP be optimized for better key generation from strings?

The mcrypt functions in PHP can be optimized for better key generation from strings by using a strong and secure hashing algorithm to generate the key. One approach is to use the hash() function with a secure hashing algorithm like SHA-256 to generate a key from the input string. This will ensure that the key generated is strong and secure for encryption purposes.

$input_string = "my_secret_key";
$key = hash('sha256', $input_string);