The answer to this question is in the iwconfig manual.
man iwconfig

iwconfig eth1 key s:c8313

I believe you'll have better results using the hex string,however.
If you go into the password setup of your wireless ap,there should be
four hex strings,one of which is being used.
That's the string you want.
That's how mine is anyway.I was unable to connect using
just the password,btw.I tried,just before posting this.

YMMV