Polyalphabetische Substitution

In this area there are a lot of mystery caches where the idea to the solution is completely unclear. Admittedly, I'm also guilty of this. In contrast, this cache's task is clear, yet shouldn't be too easy.

It's about cracking a classic cipher. The secret of encryption can be in the cipher or in the key. While elsewhere sometimes the difficulty is finding out the cipher, and the key is an easily guessable word, it's different here: As Kerckhoffs' principle of cryptography says (shortly paraphrased, among other things): "The enemy knows the system.", so security is only in the key. Therefore, the key should not be easily guessable, and it must be broken.

If you like, you can try to find out the cipher yourself. From context, this is possible. However, as said before, this should not be the main difficulty here, so you can find here a description of the cipher. (The link leads directly to a Wikipedia article that contains the name and description. So do not click it if you want to find it out yourself.)

Cipher text:

HZSIGRFVBNMHTTENVZXYVMKMHTTWTCMJZZMTPGDGRXBJRVSVKVGDRFNVOWVZMTAPNUVAMITVRAUBMGYVXBZMXLBKLG

• Important: The cache can only be searched for in the evenings, at night or on weekends! At other times the danger of muggles is simply too big. Please respect this to avoid spoiling the cache!
• The cache is probably not really watertight. So please use a water-proof marker pen for logging. If you do not have one with you, you can find one near the cache (as long as it is not muggled). However, with a body height less than 1.70m you might need auxiliary means (which can be a bike) to get to the pen, so it's not wheelchair-accessible. The position of the pen (in thousands of minutes from the cache) is given in the cipher text.
• Of course, I'm interested, as other finders might be, how you solve the code. In the physical log book there is not much space for descriptions. Of course, you won't write them here in clear or just ROT13 encrypted. But please do not encrypt it with the same key as the cipher text above either, because there more cipher text is available, the easier decryption will get for future searchers. Instead, please use the key that you can find on this web page. To access the page use user name ps (lower-case) and the key from above (in capital letters) as the password.

Please log both there and on geocaching.com, thanks.

A coin is placed virtually in the cache. If you solve the code, you can discover it (on geocaching.com).

If you liked the mystery, you can find, though a few km away, a "bonus" cache here (unfortunately only on gc.com).