Block cipher challenge

Level: CTR mode

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Ciphertext (hexencoded), for easy copy-paste

b5fc62520213c6d8d398a46e8b3f558a4f0fff5c70ca59b8415b65993d64228b1b904070f95e69031e7e68247e213ad17130da96d6144379ea24f15efbca194b

Ciphertext (hexencoded):

b5fc62520213c6d8d398a46e8b3f558a 4f0fff5c70ca59b8415b65993d64228b 1b904070f95e69031e7e68247e213ad1 7130da96d6144379ea24f15efbca194b

Plaintext (hexencoded):

b5fc62520213c6d8d398a46e8b3f558a 7b22757365726e616d65223a20226775 657374222c202269735f677565737422 3a20747275657d090909090909090909

Plaintext:

\xb5\xfcbR\x02\x13\xc6\xd8\xd3\x98\xa4n\x8b?U\x8a {"username": "gu est", "is_guest" : true}\t\t\t\t\t\t\t\t\t

Final plaintext

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