Petushok
koekeloekoe kykyliky kukeleku cock-a-doodle-doo kukko kiekuu cocorico kikeriki kikiriku kukuriku kukuriku kukareku chicchirichi kokekokko kkokkodek kko wo-wo-wo ghoo-ghoo-lee ghoo-ghoo cucurigu kuk-do-kuk kuk-kurri-kuuu ek-i-ek-ek kuckeliku co-co-co...
There is a misconfiguration in Dockerfile which lead to opcode_ids.h being copied to "include" instead of "Include". Python built without opcode shuffling and the task became as easy as using pycdc and z3 :(
There is web application based on flask library. Default page redirects you to
http://localhost:8080/?logo=petushok
Application takes logo param and if there is no extension, it tries to guess the extension of the file in current folder. For example:
petushok => petushok.png
and
petushok.png => petushok.png
Content of the file is read, encoded to base64 and inserted to HTML body. If you try to pass a folder instead of a file, you will receive debug information inside the HTML page:
<!-- DEBUG
list of available files:
__pycache__
server.pyc
wsgi.pyc
helper.pyc
templates
wsgi.py
server.py
petushok.png
-->
To sum up: you can download any file including server.py. You can also download helper.pyc which is used for validation of the secret.
Straightforward move would be to decode helper.pyc into helper.py and get all the logic used to validate the secret. This will not work out because it is compiled by bad python. The difference between python and bad python that all opcode values have been shuffled.
To proceed you can download server.py and corresponding server.pyc then compare it with the proper server.pyc to spot the difference. Then you can convert bad helper.pyc to good helper.pyc, decode it and inverse the operations done on the secret.
There's apparently many solves for the equation, for example z3 outputs [secret = 3965251753348952990461306387064706394071645273297028234756978954838] which is also a valid secret.
http://localhost:8080/?logo=petushok&secret=20378257353180406617201586284835596680265125727239853295990471852018019390038
SAS{kuP1l_muzh1k_p3Tuh4_4_0n_3mu_k4K_r3z}
Solved by: 36 teams