TheRomanXpl0it

backdoorctf 2017 - ecb Writeup

by rop2bash
September 24, 2017

We know that images encypted with an ECB algorithm leave some traces or pattern of the original image ex..

img1

Original encrypted image 1

img2

Original encrypted image 2

Well those don’t resemble ECB encrypted images, but we are pure hearted and innocent so we decide to believe in the challenge name and description and start playing around with the images in GIMP and Stegosolve.

After some time we start seeing something:

img1

Image 1 with purple patterns highlighting possible characters

Image 1 with black patterns highlighting possible characters

img2

Image 2 with different purple patterns highlighting possible characters

Image 2 with black patterns highlighting possible characters

By overlapping the images and tracing over the lines we can more or less read the flag.

Overlayed and edited image revealing handwritten flag

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