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Stream Ciphers and Message Integrity

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One of my favorite things to do around Christmas is to participate in SANS Holiday Hack Challenges. These challenges are a fun way to learn and practice hacking skills. They are released once a year around Christmas and cover a broad range of technologies, tools and hacking techniques. Aside from the high quality of the exercises in an extremely gamified environment, these challenges are: 1) absolutely free; 2) available indefinitely, so folks can play year-round, going back to past challenges as they wish.

The 2016 challenge included many tasks such as reverse engineering a mobile application, Linux hacking, password cracking, network dump analysis and, of course, web application hacking. One of the web sites had a vulnerability allowing an attacker to modify their session cookie to escalate privileges from guest to administrator. This was trivial to accomplish after getting possession of the application’s source code along with the hardcoded encryption key. But what if the key was not known?

This article will demonstrate a practical attack on RC4 ciphertext to make controlled changes in the decrypted plaintext without knowing the encryption key. The technique relies on certain properties of stream ciphers.

Shadow Bank pwn: Cheating a Hackathon for Fun and Profit

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Introduction

A few weeks ago my friend (1) and I attended a hackathon sponsored by a local ISSA chapter (2). The hackathon was a hands-on event where participants learned about common web application vulnerabilities in a fun, gamified environment. The technical platform for this hackathon was provided by Security Innovation (3).

At the end of the event, the two of us finished first and second, with nearly half of the available points each. Security Innovation, however, graciously kept the game open for a few more days to give the participants an opportunity to continue to play and learn.

We used this opportunity to find and exploit more vulnerabilities in the application, and ultimately discover the one that allowed us to completely own the application server.