Hacker101 Encrypted Pastebin

By knowing the manipulated ciphertext byte and the desired padding value, the attacker can deduce the original plaintext byte.

Most implementations use Advanced Encryption Standard with a 256-bit key in Cipher Block Chaining mode.

The Hacker101 CTF Encrypted Pastebin challenge involves a padding oracle vulnerability in AES-CBC encryption, allowing full data decryption and forgery of encrypted payloads. Exploitation involves analyzing server error responses to decrypt the post token and using bit-flipping to inject SQL payloads, ultimately revealing the flags. A detailed walkthrough of this process can be found in this blog post CTF — Hacker101 — Encrypted Pastebin | by Ravid Mazon

Hacker101, a free web security training platform from HackerOne, includes an “Encrypted Pastebin” as both a demonstrated tool and a Capture The Flag (CTF) challenge. The educational goals are: hacker101 encrypted pastebin

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

Since XOR is invertible, we can solve for the new ciphertext byte C'[i] : C'[i] = P[i] ^ x ^ C[i]

As he re-watched the video, Ethan noticed a subtle mention of a steganography tool used to hide a secret message within an image. A few minutes of digging led him to a Hacker101 GitHub repository containing a Python script for the tool. By knowing the manipulated ciphertext byte and the

While manual bit-flipping verifies the bug, automated tools make exploitation practical. PadBuster is a highly effective command-line script designed to automate padding oracle attacks.

After retrieving database contents, participants discover a URL that corresponds to a previous pastebin entry—and that entry contains the third flag.

: You iterate through possible byte values (0-255) until the server stops reporting a padding error. This confirms that the last byte of the decrypted block matches the expected padding value (e.g., 0x01 ). In this scenario, the application uses Cipher Block

To collect all flags within this challenge, reading existing data might not be enough. You may need to access administrative pastes or execute unauthorized actions. This requires encrypting your own malicious plaintext string without knowing the secret key.

"title":"test","body":"test","flag":"^FLAG^[REDACTED]$FLAG$"

The tool will output a newly minted, cryptographically valid hexadecimal string. Paste this string back into your browser URL parameter box ( ?post=[FORGED_HEX] ), hit enter, and the application will decrypt it as valid, granting you unauthorized access to the underlying sensitive data and the remaining flags. 4. Root Cause Analysis