Description
array 
mcrypt_module_get_supported_key_sizes ( string algorithm [, string lib_dir] )
     Returns an array with the key sizes supported by the specified algorithm.
     If it returns an empty array then all key sizes between 1 and
     mcrypt_module_get_algo_key_size() are supported by the
     algorithm. The optional lib_dir parameter can
     contain the location where the mode module is on the system.
    
     See also mcrypt_enc_get_supported_key_sizes() which is
     used on open encryption modules.