Breaking the Vigenere autokey cipher

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xxxmisko
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Hello! I would like to ask everybody with vigenere autokey cipher. The type of encryption:


PlainText: THISISMYTEXT
Key: ONETHISISMYT

Ciphertext: HUMLPAEGLQVM

If has sbd autobreaker for this, please help me. Have a nice day
 

Discussion

Straight-up decryption of Vigenére is not trivial. Polyalphabetic chiphers, even simple ones, generally means you need some sort of angle to attack them. It helps a lot if you know a part of the plaintext (you can use that to deduce the key) or the length of the key (which you can then use to split the Vigenére into several monoalphabetic Caesar chipher).

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