excerpt of iwconfig man file

gistfile1.txt

      key/enc[ryption]
              Used to manipulate encryption or scrambling keys and security mode.
              To set the current encryption key, just enter the key in hex digits as XXXX-XXXX-XXXX-XXXX or XXXXXXXX.  To set a key other than the current
              key, prepend or append [index] to the key itself (this won't change which is the active key). You can also enter the key as an ASCII  string
              by using the s: prefix. Passphrase is currently not supported.
              To change which key is the currently active key, just enter [index] (without entering any key value).
              off and on disable and reenable encryption.
              The  security  mode  may be open or restricted, and its meaning depends on the card used. With most cards, in open mode no authentication is
              used and the card may also accept non-encrypted sessions, whereas in restricted mode only encrypted sessions are accepted and the card  will
              use authentication if available.
              If  you  need to set multiple keys, or set a key and change the active key, you need to use multiple key directives. Arguments can be put in
              any order, the last one will take precedence.
              Examples :
                   iwconfig eth0 key 0123-4567-89
                   iwconfig eth0 key [3] 0123-4567-89
                   iwconfig eth0 key s:password [2]
                   iwconfig eth0 key [2]
                   iwconfig eth0 key open
                   iwconfig eth0 key off
                   iwconfig eth0 key restricted [3] 0123456789
                   iwconfig eth0 key 01-23 key 45-67 [4] key [4]