Block cipher challenge

Level: CTR mode

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Ciphertext (hexencoded), for easy copy-paste

cbdcff9f90e1d8f5c4b485100924e069d56a6242b8e1dc2731e495b6a593638888b03d152f944d55125999563b427043effd096cdcd6c80e8692f305520ba85a

Ciphertext (hexencoded):

cbdcff9f90e1d8f5c4b485100924e069 d56a6242b8e1dc2731e495b6a5936388 88b03d152f944d55125999563b427043 effd096cdcd6c80e8692f305520ba85a

Plaintext (hexencoded):

cbdcff9f90e1d8f5c4b485100924e069 7b22757365726e616d65223a20226775 657374222c202269735f677565737422 3a20747275657d090909090909090909

Plaintext:

\xcb\xdc\xff\x9f\x90\xe1\xd8\xf5\xc4\xb4\x85\x10\t$\xe0i {"username": "gu est", "is_guest" : true}\t\t\t\t\t\t\t\t\t

Final plaintext

{"username": "guest", "is_guest": true}