100 points
Category: General Skills
Tags : #base64
Can you make sense of this file?
The contents of the downloaded enc_flag file appears to be base64 encoded :
$ cat enc_flag
VmpGU1EyRXlUWGxTYmxKVVYwZFNWbGxyV21GV1JteDBUbFpPYWxKdFVsaFpWVlUxWVZaS1ZWWnVh
RmRXZWtab1dWWmtSMk5yTlZWWApiVVpUVm10d1VWZFdVa2RpYlZaWFZtNVdVZ3BpU0VKeldWUkNk
MlZXVlhoWGJYQk9VbFJXU0ZkcVRuTldaM0JZVWpGS2VWWkdaSGRXCk1sWnpWV3hhVm1KRk5XOVVW
VkpEVGxaYVdFMVhSbFZrTTBKVVZXMTRWMDVHV2toalJYUlhDazFyV25sVVZXaHpWakpHZEdWRlZs
aGkKYlRrelZERldUMkpzUWxWTlJYTkxDZz09Cg==
Running a base64 decode of the contents of enc_flag :
$ base64 -d enc_flag
VjFSQ2EyTXlSblJUV0dSVllrWmFWRmx0TlZOalJtUlhZVVU1YVZKVVZuaFdWekZoWVZkR2NrNVVX bUZTVmtwUVdWUkdibVZXVm5WUgpiSEJzWVRCd2VWVXhXbXBOUlRWSFdqTnNWZ3BYUjFKeVZGZHdW MlZzVWxaVmJFNW9UVVJDTlZaWE1XRlVkM0JUVW14V05GWkhjRXRXCk1rWnlUVWhzVjJGdGVFVlhi bTkzVDFWT2JsQlVNRXNLCg==
Still looking very much like a base64 string after decoding, only slightly shorter. Given the name of this challenge and assumption is made that the base64 encoding is repeated multiple times.
During the CTF event I solved this challenge manually by chaining up the decodes in a manual fashion, which works when the number of repetitions is low (6 in this case) :
$ base64 -d enc_flag | base64 -d | base64 -d | base64 -d | base64 -d | base64 -d
picoCTF{........redacted........}
Where the actual flag value redacted for the purposes of this write up.
However for situations that may utilise higher orders of repetitions, a simply bash script to loop until solved, or base64 decode fails would be a better solution.