https://[challenge-url].ctf.hacker101.com/?post=Yv5fsCfbjgHOrIteVoMZPfs7i-C2!b...~~
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
The goal for Flag 3 is to use the SQL injection vulnerability to retrieve data from this tracking table, which contains a history of all pastebin URLs ever generated. The URL for id=1 contains the final flag.
Use algorithms like AES-GCM , which verify the integrity of the data before attempting decryption, preventing the padding oracle from being consulted. hacker101 encrypted pastebin
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
If you modify even one byte of the encrypted URL parameter, the server might return a specific error if the resulting "decrypted" data doesn't have valid padding. This is the smoking gun for a Padding Oracle Attack Breaking Down the Flags Flag 0: Playing with the URL
Hacker101 Encrypted Pastebin: A Detailed Guide to Solving the CTF https://[challenge-url]
A "padding oracle" is a server behavior that leaks information about whether the padding of a decrypted ciphertext block is correct.
The serves as a reminder that encryption without integrity is often reversible. By acting as a padding oracle, the server inadvertently provides the key to its own locks.
. In CBC mode, the ciphertext of the previous block is XORed with the plaintext of the current block. By carefully toggling bits in one block of the ciphertext, you can precisely control what the plaintext of the block becomes after decryption. Hacker101 Crypto Attacks video The URL for id=1 contains the final flag
If the server is compromised, the logs show GET /paste/abc . They do not show the decryption key. An attacker who steals the database gets only encrypted data.
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.