The Twenty Doors (ROOM 9)

Question

This is part of The Twenty Doors series.
The previous one is The Twenty Doors (ROOM 8)
The next one is The Twenty Doors (ROOM 10)

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When you go into Room 9, there is a strange hint, signed by 'Dr. X':

Duplicates, go forth! The hint key is keyed with a key of key! ovnr wPraor o aZcdsua fretsfdes
- Dr. X

There is a rather confusing hint:
The hint key is keyed with a key of key! Sfb lkgm ygofbq vkr trba ex sfb Dbqlkmr gm VVG. Sfks'r sfb nmjx fgms xnt'qb dbssgmd ex abygofbqgmd sfgr rsqgmd!

And, last, the keypad: [1][2][3][4][5] [ENTER]

The next door will be added when this door is solved!

Answer 1

The hint on the wall Sfb lkgm ygofbq vkr trba ex sfb Dbqlkmr gm VVG. Sfks'r sfb nmjx fgms xnt'qb dbssgmd ex abygofbqgmd sfgr rsqgmd is:

The main cipher was used by the Germans in WWI. That's the only hint you're getting by deciphering this string using Keyed Caesar with key KEY

ovnr wPraor o aZcdsua fretsfdes decrypted is:

Press four to advance forwards using the UBCHI cipher with key KEYKEY

To get to the next room, we must press:

4