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Python cipher and encoding problems

Codes, checksums and secret messages in Python, as problems with tests that check your answer.

Start with Atbash Cipher

Beginner

  1. 211. Atbash CipherAn ancient cipher that reads the alphabet in a mirror30 XP6 min
  2. 240. Morse CodeTap out a message in dots and dashes35 XP8 min
  3. 251. Luhn ChecksumCatch a mistyped card number before the payment goes through40 XP8 min

Intermediate

  1. 277. Run-Length DecodingUnpack a squeezed string of counts and letters back to full size60 XP10 min
  2. 294. Valid ISBNIs this book number real, or did someone slip on the keyboard?65 XP12 min
  3. 311. Vigenere CipherThe keyword cipher that went unbroken for three centuries70 XP14 min
  4. 328. Base64 by HandTurn any bytes into plain letters that survive a trip through email80 XP18 min
  5. 329. Columnar Transposition CipherScramble a message by reading its columns in keyword order80 XP16 min

Advanced

  1. 348. Crack the Caesar CipherNo key? Let the shape of English give the secret away120 XP22 min
  2. 358. LZW CompressionThe dictionary trick inside GIF images: learn phrases while you read125 XP25 min
  3. 366. Huffman Code LengthHow small can a message get when common letters get the shortest codes?130 XP25 min
  4. 373. Valid UTF-8Is this stream of bytes real text, or a corrupted file?130 XP25 min
  5. 391. Playfair CipherThe pen-and-paper cipher that encrypts letters two at a time140 XP30 min

Expert

  1. 471. Repair a Hamming CodeA message from deep space with flipped bits: put every one of them back240 XP45 min
  2. 479. The Enigma MachineRebuild the rotor machine whose secret messages shaped a world war250 XP55 min

Other topics

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