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.
CryptographyLevel 102. 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…
CryptographyLevel 111. Decode the Caesar Cipher
The Caesar cipher is one of the oldest classical ciphers used by Julius Caesar. It encrypts by shifting alphabet…
CryptographyLevel 114. ROT13 Magic
ROT13 (Rotate 13) is a type of Caesar cipher that shifts the alphabet by 13 letters. Interesting feature of ROT13:…
CryptographyLevel 2AES-ECB Mode Weakness
ECB leaks repeated block patterns. This introductory task first checks the difference between encryption and encoding.…
CryptographyLevel 2RC4 Stream Cipher Weakness
RC4 was once widely used but is now deprecated. This introductory task focuses on recognizing the provided data…
CryptographyLevel 2Vigenere Cipher Decryption
Decrypt a Vigenere cipher when the key length is known and retrieve the flag. Ciphertext:…
CryptographyLevel 2Finding Hash Collisions
MD5 collisions are practical. Hashes with broken collision resistance must not be used for security-sensitive…
CryptographyLevel 2Hash Length Extension Attack
Simple signatures such as hash(secret || message) can be vulnerable to length extension attacks with Merkle-Damgard…
CryptographyLevel 2Padding Oracle Basics
Padding oracle attacks use error differences as a plaintext recovery signal. This introductory task decodes leaked…
CryptographyLevel 2Rainbow Table Attack
Unsalted fast password hashes can often be reversed with precomputed lookup databases. Reverse the given MD5 hash. MD5…
CryptographyLevel 2One-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.…
CryptographyLevel 2Predictable Randomness
Pseudo-random output with a fixed seed is reproducible and must not be used for cryptographic secrets. Flag generation…
CryptographyLevel 2Breaking Small RSA Keys
Factor a tiny RSA modulus, recover the private exponent, and decrypt a list of ciphertext values. Public key and…
CryptographyLevel 4Cryptanalysis - 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…
CryptographyLevel 5Cryptanalysis - RSA e=3 Broadcast Attack
broadcast.json contains the same plaintext encrypted with unpadded RSA e=3 under three pairwise-coprime moduli.…