The Encrypted Pastebin is a CTF challenge presented as a web application that purports to be "the most secure pastebin on the internet." The site claims to use AES-128 encryption, assuring users that their data is safe because the key is never stored in the database.
: Without a Message Authentication Code (MAC) like HMAC, an attacker can modify ciphertext to change the resulting plaintext (Bit-flipping attacks).
def test_padding(url, block): # Modifies the ciphertext and checks for padding errors # Returns True if valid padding, False otherwise pass hacker101 encrypted pastebin
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.
The Hacker101 team continued to create challenging and engaging content, pushing students to their limits. And Ethan, now a respected member of the community, looked forward to the next challenge, ready to take on whatever the world of cybersecurity had in store for him. The Encrypted Pastebin is a CTF challenge presented
This article provides a comprehensive walkthrough of the challenge, explaining each flag in detail, the cryptographic principles involved, and the broader lessons for bug bounty hunters and penetration testers.
The is one of the more formidable challenges in the Hacker101 CTF (Capture The Flag) platform, requiring a deep dive into both web exploitation and advanced cryptography. Rated with a hard difficulty level and containing four flags , this challenge serves as a practical lesson in how even "military-grade" 128-bit AES encryption can be bypassed if the implementation is flawed. The Core Vulnerability: Padding Oracle Attack A few minutes of digging led him to
Decrypting the entire post ciphertext yields a JSON payload. Hidden in this JSON is the second flag. Decrypting this data yourself, or using a ready-made script, is a rite of passage for this challenge. As the application boasts it doesn't store the key, the flag is hidden in the encrypted data itself.
Scripting this logic is required for efficiency. The python script automates this process. It uses the fact that if we set the last byte of C' to X and the padding validates, we infer that IS[15] XOR X = 0x01 . From this, the plaintext is derived. The process repeats for each block.
Ethan's first instinct was to investigate the Pastebin link. He navigated to the site and was presented with a sea of gibberish - the encrypted text was seemingly unreadable. The description read: " Decrypt with password: h101? ". Ethan's eyes lit up; this was a challenge.
