Attacking ECB

Fri, 17 Apr 2015 00:00:00 +0000

On a recent engagement, I came across Electronic Code Book (ECB) encrypted data. While there’s a plethora of documentation about performing bit flipping in ECB, I couldn’t find any decent writeups on how to perform adaptive chosen plaintext attacks to recover ciphertext.

In ECB mode, each block of plaintext is encrypted independently with the key as illustrated by the diagram below.

(Source: Wikipedia)

Since each block of plaintext is encrypted with the key independently, identical blocks of plaintext will yield identical blocks of ciphertext. The classic and poignant example of this property is an encrypted image of the Linux mascot, Tux. Below are three images, the original Tux image, an ECB encrypted Tux and a CBC encrypted Tux. The ECB encrypted Tux leaves visible artifacts whereas the CBC encrypted Tux looks like random data.

AES on Zach Grace

Attacking ECB