WEP can be configured to either use 40 or 104 bit keys. Use the 104 bit keys for increased security (or even better: switch to WPA2 for real security). The valid formats are as follows:
- For 104 bit WEP: 13 printable ASCII characters or 26 hexadecimal digits
- For 40 bit WEP: 5 printable ASCII characters or 10 hexadecimal digits
Many Wi-Fi access points allow to enter a passphrase which is used to generated (sometimes multiple) WEP keys. You normally have to use the WEP key, the passphrase usually does not work.
Note: hexadecimal digits are 0 to 9 and A to F