English [EKOPARTY PRE-CTF 2015] [Cry25 – BASE unknown] Write Up

Description

BASE unknown

Description: IVFU662CIFJUKXZTGJPWG2DBNRWH2===

Resolution

It seems to be a string encoded into base64, but without lower letters.
With the challenge title as hint, we tried base32.

You’ll say “ABC…XYZ + 012…789 = 26 + 10 = 35 and not 32 ? WTF!”
In fact only numbers 234567 are used : 26 letters + 6 digits = 32 😉

We opened our dear python shell:
$ python

>>> import base64
>>> text = 'IVFU662CIFJUKXZTGJPWG2DBNRWH2==='
>>> print base64.b32decode(text)
EKO{BASE_32_chall}

Flag was : EKO{BASE_32_chall}

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