Block cipher challenge

Level: CTR mode

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Ciphertext (hexencoded), for easy copy-paste

856591c9dbc686231fcc66be6c5d4e7b2a8fc4558aeeea911fe36855743913a51aa8b8ec06f73adab30708e51c86aac015f7ebddd28b93aa535922288c821fd7

Ciphertext (hexencoded):

856591c9dbc686231fcc66be6c5d4e7b 2a8fc4558aeeea911fe36855743913a5 1aa8b8ec06f73adab30708e51c86aac0 15f7ebddd28b93aa535922288c821fd7

Plaintext (hexencoded):

856591c9dbc686231fcc66be6c5d4e7b 7b22757365726e616d65223a20226775 657374222c202269735f677565737422 3a20747275657d090909090909090909

Plaintext:

\x85e\x91\xc9\xdb\xc6\x86#\x1f\xccf\xbel]N{ {"username": "gu est", "is_guest" : true}\t\t\t\t\t\t\t\t\t

Final plaintext

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