Block cipher challenge

Level: CTR mode

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Ciphertext (hexencoded), for easy copy-paste

8fbfb55b4945f495632a8919ae7978978d4339518a379ebb68b50379e97ea9927dc83ad76d299c474249750fe6abb56edbca7732444c2671fe946e61ed8ec92a

Ciphertext (hexencoded):

8fbfb55b4945f495632a8919ae797897 8d4339518a379ebb68b50379e97ea992 7dc83ad76d299c474249750fe6abb56e dbca7732444c2671fe946e61ed8ec92a

Plaintext (hexencoded):

8fbfb55b4945f495632a8919ae797897 7b22757365726e616d65223a20226775 657374222c202269735f677565737422 3a20747275657d090909090909090909

Plaintext:

\x8f\xbf\xb5[IE\xf4\x95c*\x89\x19\xaeyx\x97 {"username": "gu est", "is_guest" : true}\t\t\t\t\t\t\t\t\t

Final plaintext

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