XOR Pain

Level: 3 Score 30 Category crypto

There is a piece of code and a text file. Make it work!!

Link: SecurityValley/PublicCTFChallenges/crypto/xor_hell

Analysis

1. xor_hell.py performs standard XOR operation on the flag

2. We have the output (in hex format)

3. Key is 0. It's not a real key, but rather redacted value

Solution

Since we know that XOR is a symmetrical encryption we can abuse that.

By using Crib Attack method we can find the key and then decrypt the flag. We can utilize the crib attack since we know that flag always starts with SecVal{

Cyberchef

Note: Bruteforcing whole flag from Cyberchef will take ages, doing chunk by chunk is faster

After doing it for other parts

Key = 6f6d: Se
Key = 676f: cV
Key = 6d67: al

6f6d676f6d67

key=6f6d67 in hex (we know this because key gets repeated).

To test the key we can use XOR from CyberChef and get the flag