How can I break a Vigenère cipher with partial plain text? I have an exercise to do regarding Vigenère encryption.

I've got the cipher text: WNZTNVIEEGTJYKRRWYUELWNZTNV
and a partial plain text: S''''R''R''''R''''PASS'''''

The key length is unknown.

The question is: is it possible to find the key and the plain text?
Regarding what I've seen in class, I don't think it's possible.

But I was wondering if it was possible in some way with a computer to find the rest of the plain text and the key?

PS: neither the plain text or the key are in English.
First guess the key length(Just try every plausible length, there aren't many).

Then for each position where you know both plain- and ciphertext, calculate the key char. If you get a contradiction, the guessed key length was wrong.
If the key length is short enough compared to the number of known pairs this will probably give you a large part of the key.