Hacker101 Encrypted: Pastebin
If the application validates the padding after decryption and behaves differently when the padding is incorrect (e.g., throwing a "Padding Exception"), it creates a . Alternatively, if the application lacks integrity checks (like a Message Authentication Code or MAC), an attacker can precisely alter the decrypted plaintext by flipping bits in the ciphertext block directly preceding it. This is known as a CBC Bit-Flipping attack . Step-by-Step Walkthrough to the Flags Step 1: Mapping the Parameters and Error Leakage
This flag requires a deep dive into how CBC mode works. Since the server confirms whether padding is valid or invalid, it functions as a "Padding Oracle".
# Paste content cat sensitive_log.txt | securedrop encrypt
This isn’t just a toy example. Real apps have made similar mistakes: hacker101 encrypted pastebin
The pastebin uses mode. If you’ve studied crypto, you know CBC has a classic weakness: bit flipping attacks . Because each ciphertext block affects the next block’s plaintext, changing a byte in block N-1 toggles the corresponding byte in block N’s plaintext.
The application is a simple text-sharing site. It allows users to paste text and secure it with a password.
The challenge in Hacker101 CTF is a classic exercise in identifying and exploiting a Padding Oracle Attack . In this scenario, the application uses Cipher Block Chaining (CBC) mode for encryption but leaks information through its error responses, allowing an attacker to decrypt data without the key. Technical Overview If the application validates the padding after decryption
A list of other beginner-friendly Hacker101 challenges Let me know how you'd like to continue with your learning . medium.com·Ravid Mazon CTF — Hacker101 — Encrypted Pastebin | by Ravid Mazon
New P1=P1⊕C0⊕New C0New cap P sub 1 equals cap P sub 1 circled plus cap C sub 0 circled plus New cap C sub 0 Scenario: Modifying Parameters
AES is a block cipher that operates on 16-byte blocks. If the data being encrypted is not a multiple of 16 bytes, padding (like PKCS#7) is added. Upon decryption, the application checks this padding. If the padding is incorrect, an error is triggered. Why the Challenge is Vulnerable Step-by-Step Walkthrough to the Flags Step 1: Mapping
To solve this, many participants use the Perl script, as recommended in this medium article. Run PadBuster: padbuster -encoding 0 Use code with caution.
This article provides a comprehensive walkthrough, understanding, and solution approach to the challenge, focusing on its core vulnerabilities: Padding Oracle Attacks and Bit Flipping . 1. Introduction to the Challenge
Change the last byte of the first block from 0x00 to 0xff .
Upon starting the challenge, participants are presented with a basic web application that claims: "We've developed the most secure pastebin on the internet. Your data is protected with military-grade 128-bit AES encryption. The key for your data is never stored in our database, so no hacker can ever gain unauthorized access".
In the spirit of OpsSec and data sovereignty, I wanted to share a lightweight tool I've been working on. We all know the risks of using public pastebins for sensitive logs, configuration files, or API keys. Even "secret" links are often crawled, and you're trusting a third party with your plaintext data.
