Block cipher challenge

Level: CTR mode

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Ciphertext (hexencoded), for easy copy-paste

40540f90d6f9242e2cf397dacbfd60cdc0321543ce830f4c10c451a6865298d437da95c5e7c4a1d9b6c52cea0c3acc26f5c70ecd2103215356a1e230e183e4e4

Ciphertext (hexencoded):

40540f90d6f9242e2cf397dacbfd60cd c0321543ce830f4c10c451a6865298d4 37da95c5e7c4a1d9b6c52cea0c3acc26 f5c70ecd2103215356a1e230e183e4e4

Plaintext (hexencoded):

40540f90d6f9242e2cf397dacbfd60cd 7b22757365726e616d65223a20226775 657374222c202269735f677565737422 3a20747275657d090909090909090909

Plaintext:

@T\x0f\x90\xd6\xf9$.,\xf3\x97\xda\xcb\xfd`\xcd {"username": "gu est", "is_guest" : true}\t\t\t\t\t\t\t\t\t

Final plaintext

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