What you will learn
- Distinguish encoding, hashing, and encryption
- Recognize properties of common ciphers
- Follow a repeatable cryptanalysis workflow
Cryptography CTF Challenges
Work from classical ciphers to modern cryptographic concepts while learning the difference between encoding, hashing, and encryption.
Cryptography challenges
15 challenges available.
Cryptography Level 1 02. Hidden Secret - Base64 Decode
Base64 is an encoding method used to transmit binary data as text. It's not encryption, but it's often used for…
Cryptography Level 1 11. Decode the Caesar Cipher
The Caesar cipher is one of the oldest classical ciphers used by Julius Caesar. It encrypts by shifting alphabet…
Cryptography Level 1 14. ROT13 Magic
ROT13 (Rotate 13) is a type of Caesar cipher that shifts the alphabet by 13 letters. Interesting feature of ROT13:…
Cryptography Level 2 AES-ECB Mode Weakness
ECB leaks repeated block patterns. This introductory task first checks the difference between encryption and encoding.…
Cryptography Level 2 RC4 Stream Cipher Weakness
RC4 was once widely used but is now deprecated. This introductory task focuses on recognizing the provided data…
Cryptography Level 2 Vigenere Cipher Decryption
Decrypt a Vigenere cipher when the key length is known and retrieve the flag. Ciphertext:…
Cryptography Level 2 Finding Hash Collisions
MD5 collisions are practical. Hashes with broken collision resistance must not be used for security-sensitive…
Cryptography Level 2 Hash Length Extension Attack
Simple signatures such as hash(secret || message) can be vulnerable to length extension attacks with Merkle-Damgard…
Cryptography Level 2 Padding Oracle Basics
Padding oracle attacks use error differences as a plaintext recovery signal. This introductory task decodes leaked…
Cryptography Level 2 Rainbow Table Attack
Unsalted fast password hashes can often be reversed with precomputed lookup databases. Reverse the given MD5 hash. MD5…
Cryptography Level 2 One-Time Pad Key Reuse Attack
A one-time pad is safe only when the key is used once. Reusing the key lets known plaintext recover other plaintexts.…
Cryptography Level 2 Predictable Randomness
Pseudo-random output with a fixed seed is reproducible and must not be used for cryptographic secrets. Flag generation…
Cryptography Level 2 Breaking Small RSA Keys
Factor a tiny RSA modulus, recover the private exponent, and decrypt a list of ciphertext values. Public key and…
Cryptography Level 4 Cryptanalysis - DSA Nonce Reuse Key Recovery
signatures.json contains two DSA signatures that reused the same nonce. Recover nonce k and private key x from the…
Cryptography Level 5 Cryptanalysis - RSA e=3 Broadcast Attack
broadcast.json contains the same plaintext encrypted with unpadded RSA e=3 under three pairwise-coprime moduli.…