My walkthrough of the Cryptopals challenges

The cryptopals challenges (https://cryptopals.com/) are a series of challenges on practical cryptography.

SPOILER ALERT: If you want to solve the challenges without being given the solution, you should probably not browse this repository.

The following is my walkthrough of these challenges using the Python programming language. I try not only to solve them, but to explain how I do it.

This is a work in progress. I am solving new challenges every now and then, but also I am improving the explanations I give regularly.

The file libmatasano.py contains the functions that are created in one challenge and re-used in other challenges.

Tables of Contents

• Set 1: Basics (Challenges 1 to 8)
• Convert hex to base64
• Fixed XOR
• Single-byte XOR cipher
• Detect single-character XOR
• Implement repeating-key XOR
• Break repeating-key XOR
• AES in ECB mode
• Detect AES in ECB mode
• Set 2: Block Crypto
  • Challenges 9 to 13
  • Implement PKCS#7 padding
  • Implement CBC mode
  • An ECB/CBC detection oracle
  • Byte-at-a-time ECB decryption (Simple)
  • ECB cut-and-paste
  • Challenge 14: Byte-at-a-time ECB decryption (Harder)
  • Challenges 15 and 16: PKCS#7 padding validation & CBC bitflipping attacks
• Set 3: Block & Stream Crypto
  • Challenge 17: The CBC padding oracle
  • Challenge 18: Implement CTR, the stream cipher mode
  • Challenges 19 and 20: Break fixed-nonce CTR mode using substitutions & Break fixed-nonce CTR statistically
  • Challenge 21: Implement the MT19937 Mersenne Twister RNG
  • Challenge 22: Crack an MT19937 seed
  • Challenge 23: Clone an MT19937 RNG from its output
  • Challenge 24: Create the MT19937 stream cipher and break it
• Set 4: Stream crypto and randomness
  • Challenge 25: Break "random access read/write" AES CTR
  • Challenge 26: CTR bitflipping
  • Challenge 27: Recover the key from CBC with IV=Key
  • Challenges 28 and 29: Implement a SHA-1 keyed MAC & Break a SHA-1 keyed MAC using length extension
  • Challenge 31: Implement and break HMAC-SHA1 with an artificial timing leak