PicoCTF2019

Hello, here’s my take on the picoCTF2019 reverse engineering asm challenges. If you don’t know assembly, please watch a few tutorials on it: asm1 – Points: 200 CMP: Compares the first source operand with the second source operand and sets the status flags in the EFLAGS register according to the results. The comparison is performed by subtracting the second operand from the first operand and then setting the status flags in the same manner as the SUB instruction. When an immediate value is used as an operand, it is sign-extended to the length of the first operand. ...

I’m always late to the party but here’s my solutions to the PicoCTF2019 Vault Doors challenges from the reverse engineering section. I did it this mainly to improve my skills and hopefully to learn some new things. vault-door-training – Points: 50 Your mission is to enter Dr. Evil’s laboratory and retrieve the blueprints for his Doomsday Project. The laboratory is protected by a series of locked vault doors. Each door is controlled by a computer and requires a password to open. Unfortunately, our undercover agents have not been able to obtain the secret passwords for the vault doors, but one of our junior agents obtained the source code for each vault’s computer! You will need to read the source code for each level to figure out what the password is for that vault door. As a warmup, we have created a replica vault in our training facility. The source code for the training vault is here: VaultDoorTraining.java ...

Can you spot the difference? kitters cattos. They are also available at /problems/whats-the-difference… on the shell server In order to easily solve this challenge, I’ve used xxd and cut to generate an ascii hexdump of the images: 1 2 3 4 ➜ Downloads xxd kitters.jpg | cut -d ' ' -f 11 > kittens_text.txt ➜ Downloads xxd cattos.jpg | cut -d ' ' -f 11 > cattos_text.txt Since I wanted to do a per character diff I wrote the following Python script: 1 2 3 4 5 6 7 8 9 10 11 12 13 <pre class="wp-block-prismatic-blocks">```python def main(): new = open("cattos_text.txt") old = open("kittens_text.txt") old_file = old.readlines() new_file = new.readlines() print("Loaded lines", len(old_file), len(new_file)) for line in zip(old_file, new_file): for number, old_char in enumerate(line[0]): if old_char != line[1][number]: print(line[1][number], end="") main() And finally run the script: ...