Block cipher challenge

Level: CTR mode

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Ciphertext (hexencoded), for easy copy-paste

9f61a1da6a74fca1ddf46fa8f370900978ef8c013b5090330ad4c40eae4a1c0f9f255c5d629631365153a3e7ca21d60b84be4bf7c30fc62b389eddfabf71ad77

Ciphertext (hexencoded):

9f61a1da6a74fca1ddf46fa8f3709009 78ef8c013b5090330ad4c40eae4a1c0f 9f255c5d629631365153a3e7ca21d60b 84be4bf7c30fc62b389eddfabf71ad77

Plaintext (hexencoded):

9f61a1da6a74fca1ddf46fa8f3709009 7b22757365726e616d65223a20226775 657374222c202269735f677565737422 3a20747275657d090909090909090909

Plaintext:

\x9fa\xa1\xdajt\xfc\xa1\xdd\xf4o\xa8\xf3p\x90\t {"username": "gu est", "is_guest" : true}\t\t\t\t\t\t\t\t\t

Final plaintext

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