Hacker101 Encrypted Pastebin File

: Without a Message Authentication Code (MAC) like HMAC, an attacker can modify ciphertext to change the resulting plaintext (Bit-flipping attacks).

: AES-128 is secure, but using it with a vulnerable mode of operation or a leaky oracle makes it useless.

This design provides strong guarantees against several common threats:

The final flag is the most satisfying, as it combines the cryptographic techniques with a more traditional web vulnerability: (SQLi). Every page loaded by the application triggers a tracking.gif image, which likely logs the request data (like headers, IP, and the accessed URL) in a database table.

The first flag is remarkably easy to obtain. Simply by making a request to the endpoint with an invalid post parameter—such as a single character or a malformed string—the server throws an error that reveals a flag in the response. hacker101 encrypted pastebin

This article breaks down how the Encrypted Pastebin works, uncovers its underlying vulnerabilities, and provides a step-by-step walkthrough to extract the flags. Understanding the Target Application

The response reveals the url of another paste, which contains the final flag(s).

Ethan quickly wrote a Python script to extract the hidden message from an image provided in the lecture notes. The script revealed a Base64 encoded string, which, when decoded, contained a password: h101St3g0_is_fun .

As you progress through the CTF, earning 26 points makes you eligible for invitations to private bug bounty programs on HackerOne, providing a direct path from learning to earning. : Without a Message Authentication Code (MAC) like

is the previous ciphertext block (the Initialization Vector for the first block). By modifying Cn−1cap C sub n minus 1 end-sub , you directly change the resulting Pncap P sub n 3. Execute the Attack Logic

Upon entering the challenge, the application claims to use "military-grade 128-bit AES encryption" and asserts that keys are never stored in the database.

provides a practical, hands-on lesson in how supposedly "military-grade" encryption can be completely broken if implemented incorrectly Why It's a Great Learning Feature

This flag demonstrates a critical principle: . The server's error handling may prevent full decryption, but if any portion of the processing continues—such as displaying a title—an attacker can extract sensitive data. Every page loaded by the application triggers a tracking

Note the response. If the server returns a specific error text or an HTTP 500 error code for certain byte modifications, but an HTTP 404 or a regular error page for others, the Padding Oracle is confirmed. Step 2: Automated Analysis via PadBuster

If the padding bytes are structurally valid (e.g., ending in \x01 or \x02\x02 ), the server attempts to process the data. It may throw a generic "404 Not Found" or a signature error because the decrypted data is garbage.

To get the most out of Encrypted Pastebin, follow these best practices:

padbuster http://35.x.x.x/pastebin/view/ [ENCRYPTED_TOKEN] 16 -encoding 3 Use code with caution. 16 specifies the AES block size.