OTP key reuse vulnerability cracker

gistfile1.rb

class String
  # 'hello' ^ '     ' => 'HELLO'
  def ^ s2
    to_byte_array.zip(s2.to_byte_array).map { |s| s[0] ^ s[1] if s[1] }.reject(&:nil?).pack('C*')
  end

  # '68656c6c6f20776f726c64' => 'hello world'
  def hex_string_to_binary_string
    [self].pack 'H*'
  end
  
  # 'hello world' => '68656c6c6f20776f726c64'
  def binary_string_to_hex_string
    unpack('H*').first
  end
  
  # 'hello world' => [104, 101, 108, 108, 111, 32, 119, 111, 114, 108, 100]
  def to_byte_array
    unpack 'C*'
  end  
end

CIPHERS = %w[
315c4eeaa8b5f8aaf9174145bf43e1784b8fa00dc71d885a804e5ee9fa40b16349c146fb778cdf2d3aff021dfff5b403b510d0d0455468aeb98622b137dae857553ccd8883a7bc37520e06e515d22c954eba5025b8cc57ee59418ce7dc6bc41556bdb36bbca3e8774301fbcaa3b83b220809560987815f65286764703de0f3d524400a19b159610b11ef3e
234c02ecbbfbafa3ed18510abd11fa724fcda2018a1a8342cf064bbde548b12b07df44ba7191d9606ef4081ffde5ad46a5069d9f7f543bedb9c861bf29c7e205132eda9382b0bc2c5c4b45f919cf3a9f1cb74151f6d551f4480c82b2cb24cc5b028aa76eb7b4ab24171ab3cdadb8356f
32510ba9a7b2bba9b8005d43a304b5714cc0bb0c8a34884dd91304b8ad40b62b07df44ba6e9d8a2368e51d04e0e7b207b70b9b8261112bacb6c866a232dfe257527dc29398f5f3251a0d47e503c66e935de81230b59b7afb5f41afa8d661cb
32510ba9aab2a8a4fd06414fb517b5605cc0aa0dc91a8908c2064ba8ad5ea06a029056f47a8ad3306ef5021eafe1ac01a81197847a5c68a1b78769a37bc8f4575432c198ccb4ef63590256e305cd3a9544ee4160ead45aef520489e7da7d835402bca670bda8eb775200b8dabbba246b130f040d8ec6447e2c767f3d30ed81ea2e4c1404e1315a1010e7229be6636aaa
3f561ba9adb4b6ebec54424ba317b564418fac0dd35f8c08d31a1fe9e24fe56808c213f17c81d9607cee021dafe1e001b21ade877a5e68bea88d61b93ac5ee0d562e8e9582f5ef375f0a4ae20ed86e935de81230b59b73fb4302cd95d770c65b40aaa065f2a5e33a5a0bb5dcaba43722130f042f8ec85b7c2070
32510bfbacfbb9befd54415da243e1695ecabd58c519cd4bd2061bbde24eb76a19d84aba34d8de287be84d07e7e9a30ee714979c7e1123a8bd9822a33ecaf512472e8e8f8db3f9635c1949e640c621854eba0d79eccf52ff111284b4cc61d11902aebc66f2b2e436434eacc0aba938220b084800c2ca4e693522643573b2c4ce35050b0cf774201f0fe52ac9f26d71b6cf61a711cc229f77ace7aa88a2f19983122b11be87a59c355d25f8e4
32510bfbacfbb9befd54415da243e1695ecabd58c519cd4bd90f1fa6ea5ba47b01c909ba7696cf606ef40c04afe1ac0aa8148dd066592ded9f8774b529c7ea125d298e8883f5e9305f4b44f915cb2bd05af51373fd9b4af511039fa2d96f83414aaaf261bda2e97b170fb5cce2a53e675c154c0d9681596934777e2275b381ce2e40582afe67650b13e72287ff2270abcf73bb028932836fbdecfecee0a3b894473c1bbeb6b4913a536ce4f9b13f1efff71ea313c8661dd9a4ce
315c4eeaa8b5f8bffd11155ea506b56041c6a00c8a08854dd21a4bbde54ce56801d943ba708b8a3574f40c00fff9e00fa1439fd0654327a3bfc860b92f89ee04132ecb9298f5fd2d5e4b45e40ecc3b9d59e9417df7c95bba410e9aa2ca24c5474da2f276baa3ac325918b2daada43d6712150441c2e04f6565517f317da9d3
271946f9bbb2aeadec111841a81abc300ecaa01bd8069d5cc91005e9fe4aad6e04d513e96d99de2569bc5e50eeeca709b50a8a987f4264edb6896fb537d0a716132ddc938fb0f836480e06ed0fcd6e9759f40462f9cf57f4564186a2c1778f1543efa270bda5e933421cbe88a4a52222190f471e9bd15f652b653b7071aec59a2705081ffe72651d08f822c9ed6d76e48b63ab15d0208573a7eef027
466d06ece998b7a2fb1d464fed2ced7641ddaa3cc31c9941cf110abbf409ed39598005b3399ccfafb61d0315fca0a314be138a9f32503bedac8067f03adbf3575c3b8edc9ba7f537530541ab0f9f3cd04ff50d66f1d559ba520e89a2cb2a83
32510ba9babebbbefd001547a810e67149caee11d945cd7fc81a05e9f85aac650e9052ba6a8cd8257bf14d13e6f0a803b54fde9e77472dbff89d71b57bddef121336cb85ccb8f3315f4b52e301d16e9f52f904
].map &:hex_string_to_binary_string

TARGET = '32510ba9babebbbefd001547a810e67149caee11d945cd7fc81a05e9f85aac650e9052ba6a8cd8257bf14d13e6f0a803b54fde9e77472dbff89d71b57bddef121336cb85ccb8f3315f4b52e301d16e9f52f904'.hex_string_to_binary_string

key = "\0" * CIPHERS.map(&:length).max

# Step horizontally through each byte
TARGET.length.times do |x|
  max_probability = 0.5

  # Step vertically through every other cipher
  # If we get _mostly_ letters, the plain text of that chacter is probably a space (' ', 0x20)
  CIPHERS.each_with_index do |c1, y|
    # puts "x = #{x}, y = #{y}"
    m_xor_m = CIPHERS.map { |c2| c1.getbyte(x) ^ c2.getbyte(x) }
    
    # XOR guides:
    # 'a' ^ 'a'..'z' = 0..27
    # 'a' ^ 'A'..'Z' = 32..59
    # ' ' ^ 'a'..'z' = 65..90 ('A'..'Z')
    # ' ' ^ 'A'..'Z' = 97..122 ('a'..'z')
    space_count = m_xor_m.select { |byte| (65..90).include?(byte) || (97..122).include?(byte) }.length
    
    probability = space_count / CIPHERS.length.to_f
    if probability > max_probability
      max_probability = probability
      key[x] = (c1.getbyte(x) ^ 0x20).chr
      puts "!!! key[#{x}] = #{key.getbyte(x)}, Probability = #{space_count / CIPHERS.length.to_f}"
    end
    # puts m_xor_m.inspect
  end
end

puts "key = #{key.inspect}"
puts TARGET ^ key
puts CIPHERS.map { |c| c ^ key }

Hoisn