To all solvers of this challenge,
some of you may encounter the same problems as Integral. It is obviously not possible to decrypt all five messages correctly with the same key. This may be due to encryption errors some of the secret agents made during encryption of their message (encryption errors made during an encryption by hand seems to me a very realistic scenario). If for instance the messages 2 and 3 will be decrypted correctly, then message 1 contains an error, but its only one wrong character. If you adapt the key in such a way, that message 1 will be decrypted correctly, messages 2 and 3 will show up some decryption errors. Its difficult to decide, who made the errors.
I assumed, that the encryption errors are due to the secret agents, who encrypted the messages. But it would not be the first time in the history of MTC3, that some errors in the description of a challenge have been made during the generation of the pdf file of the challenge. Can the author of this challenge confirm, that the errors have been already in the original messages?