[CentOS] wep key generator

Dear All,

I have this same problem on my ubuntu as in my Centos linux.

when i use NetworkManager to connect to my NetGear Access Point with
WEP security, the passphrase seems that do not make the correct KEY,
so i had to check in the NetGear and enter it manually in EX mode,
using iwconfig on CentOS and the networking utility in ubuntu.

Ok, after this introduction this is my question.
Do you know any WEP Key generator starting from a passphrase? for linux?
i have found a lot for windows and on-line wich work really good,
http://www.powerdog.com/wepkey.cgi
this one generates exactly the same as my NetGear AP.
but offcourse if I can't connect to the network I can't use an online tool :(

any ideas?
thanks
Guillermo.