Block cipher challenge

Level: CTR mode

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Ciphertext (hexencoded), for easy copy-paste

5704d5218c1a3102002600fc998a02c76e22810d4027dbcf41b33db5d45bf633ca1e6594ca766643fd5ed0ec68c23f4a90e7f4c1a15c21f1d8f3382c0d231c92

Ciphertext (hexencoded):

5704d5218c1a3102002600fc998a02c7 6e22810d4027dbcf41b33db5d45bf633 ca1e6594ca766643fd5ed0ec68c23f4a 90e7f4c1a15c21f1d8f3382c0d231c92

Plaintext (hexencoded):

5704d5218c1a3102002600fc998a02c7 7b22757365726e616d65223a20226775 657374222c202269735f677565737422 3a20747275657d090909090909090909

Plaintext:

W\x04\xd5!\x8c\x1a1\x02\x00&\x00\xfc\x99\x8a\x02\xc7 {"username": "gu est", "is_guest" : true}\t\t\t\t\t\t\t\t\t

Final plaintext

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