Block cipher challenge

Level: CTR mode

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Ciphertext (hexencoded), for easy copy-paste

78f614c001b799a9465afb55a4fb7c5cd84cf36d159b2f33a1e4efdba2abe14d8778b83ad61ab2cde872529370c09cd544959a144301b84cde72f25c3ea4daaa

Ciphertext (hexencoded):

78f614c001b799a9465afb55a4fb7c5c d84cf36d159b2f33a1e4efdba2abe14d 8778b83ad61ab2cde872529370c09cd5 44959a144301b84cde72f25c3ea4daaa

Plaintext (hexencoded):

78f614c001b799a9465afb55a4fb7c5c 7b22757365726e616d65223a20226775 657374222c202269735f677565737422 3a20747275657d090909090909090909

Plaintext:

x\xf6\x14\xc0\x01\xb7\x99\xa9FZ\xfbU\xa4\xfb|\\ {"username": "gu est", "is_guest" : true}\t\t\t\t\t\t\t\t\t

Final plaintext

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