With the wifi key generator for Android, you can be generating a virtually unbreakable up to 504-bit key.

The app supports:
Capital letters (A-Z) with umlauts
Small-Buchstanem (a-z) with umlauts
Special characters (* # u.v.m)
Numbers (0-9)

After generating, the keys can be copied to the clipboard.

Important info: Some routers (for example Asus) do not support special characters. In the case, simply uncheck the special characters.