Find md5 hashed password with leading key

Hi,

I'm trying to find a way to revert a password.

I know the password is stored using an php routine like this:

$key = 'fixed_key_i_know';  // this is not real key

$user_md5_password = md5($key . $input_password);

for instance, if input_password is 123456, the md5 will be e86ab642c6f2d9987499776f1dc12f8f.

I know the key and hashed password, can hashcat help me with discover that? maybe with mask "fixed_key_i_know?d?d?d?d?d?d?"  ???