picoCTF 2023 – repetitions

28 March 2023 – Written by Valentin Huber – in base64, ctf, and python

Challenge

Can you make sense of this file? Download the file here.

File content:

VmpGU1EyRXlUWGxTYmxKVVYwZFNWbGxyV21GV1JteDBUbFpPYWxKdFVsaFpWVlUxWVZaS1ZWWnVh
RmRXZWtab1dWWmtSMk5yTlZWWApiVVpUVm10d1VWZFdVa2RpYlZaWFZtNVdVZ3BpU0VKeldWUkNk
MlZXVlhoWGJYQk9VbFJXU0ZkcVRuTldaM0JZVWpGS2VWWkdaSGRXCk1sWnpWV3hhVm1KRk5XOVVW
VkpEVGxaYVdFMVhSbFpSV0VKWVZGVmtNRTVHV2tWU2JYUlVDbUpXV25sVWJGcHZWbGRHZEdWRlZs
aGkKYlRrelZERldUMkpzUWxWTlJYTkxDZz09Cg==

Solution

The == at the end of the data indicates base64, the title indicates a repeated application. So I wrote a short python script:

from base64 import b64decode
data = "VmpGU1EyRXlUWGxTYmxKVVYwZFNWbGxyV21GV1JteDBUbFpPYWxKdFVsaFpWVlUxWVZaS1ZWWnVhRmRXZWtab1dWWmtSMk5yTlZWWApiVVpUVm10d1VWZFdVa2RpYlZaWFZtNVdVZ3BpU0VKeldWUkNkMlZXVlhoWGJYQk9VbFJXU0ZkcVRuTldaM0JZVWpGS2VWWkdaSGRXCk1sWnpWV3hhVm1KRk5XOVVWVkpEVGxaYVdFMVhSbGhhTTBKWVZXeG9RMlZXV2tkWGJYUlVDbUY2VmtoWmEyaEhWMGRHZEdWRlZsaGkKYlRrelZERldUMkpzUWxWTlJYTkxDZz09Cg=="
while "picoCTF" not in data:
    data = b64decode(data).decode().strip()

print(data)