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OverTheWire Krypton
 April 1, 2021    CTF

Krypton 0


Krypton 1

  • YRIRY GJB CNFFJBEQ EBGGRA
  • ROT13 decodes to: LEVEL TWO PASSWORD ROTTEN
  • Using CyberChef 🎜


Krypton 2


Krypton 3

  • Ciphertext: KSVVW BGSJD SVSIS VXBMN YQUUK BNWCU ANMJS
  • By pasting all three found texts and the ciphertext into quipqiup we get an entropy of 1.324 and the Password BRUTE


Krypton 4

  • Ciphertext: HCIKV RJOX
  • By pasting all found texts and the ciphertext into this solving tool we get the vignere key frekey
  • The password is CLEARTEXT


Krypton 5

  • ciphertext: BELOS Z
  • By pasting all found texts and the ciphertext into this solving tool we get the vignere key keylength
  • The Password is RANDOM


Krypton 6

  • Ciphertext: PNUKLYLWRQKGKBE
  • When decompiling the encryption binary, the following expression can be found which is applied to each character: 
    random_number + password[password_pos] + upper_plain_char - 'A'
  • The random_number is not really random, but rather the same each run and repeating
  • Thus by passing AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA to the encryption program, we essentially get random + password + 'A' - 'A'
  • The string output repeats EICTDGYIYZKTHNSIRFXYCPFUEOCKRN
  • This string is already the vignere key of the encryption
  • Thus we can use CyberChef 🎜 to obtain the password
  • The password is LFSRISNOTRANDOM