Block cipher challenge

Level: CTR mode

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Ciphertext (hexencoded), for easy copy-paste

8704287f0fa8012bd1ad5e119e2b0e5e3775d48f804b0591601077690d8560bf10cc4c25cc4eb1211a46fc7c91f3e28b9cd9caa41cf65d35c7dbcc9ea7a270ae

Ciphertext (hexencoded):

8704287f0fa8012bd1ad5e119e2b0e5e 3775d48f804b0591601077690d8560bf 10cc4c25cc4eb1211a46fc7c91f3e28b 9cd9caa41cf65d35c7dbcc9ea7a270ae

Plaintext (hexencoded):

8704287f0fa8012bd1ad5e119e2b0e5e 7b22757365726e616d65223a20226775 657374222c202269735f677565737422 3a20747275657d090909090909090909

Plaintext:

\x87\x04(\x7f\x0f\xa8\x01+\xd1\xad^\x11\x9e+\x0e^ {"username": "gu est", "is_guest" : true}\t\t\t\t\t\t\t\t\t

Final plaintext

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