analyze1.rb

#!/usr/bin/ruby

def analyze(encrypted_hex)
  guess = {
    'CB' => ' ', # 'A',
    '9C' => 'e', # 'B',
    'BA' => 't', # 'C',
    'DA' => 'o', # 'D',
    '0D' => 's', # 'E', 
    '24' => 'n', # 'F', 
    'C2' => 'i', # 'G', 
    'F0' => 'a', # 'H', 
    '1C' => 'r', # 'I', 
    '97' => 'l', # 'J', 
    'CD' => 'c', # 'K', 
    '7D' => 'd', # 'L', 
    'F9' => 'f', # 'M', 
    '4D' => 'h', # 'N', 
    '58' => 'u', # 'O', 
    '3F' => 'p', # 'P', 
    '21' => ',', # 'Q', 
    '2C' => 'y', # 'R', 
    '08' => 'g', # 'S', 
    'E4' => 'm', # 'T', 
    'D3' => 'b', # 'U', 
    '25' => '-', # 'V', 
    '07' => 'w', # 'W', 
    '78' => '"', # 'X',
    'A9' => 'k', # 'Y', 
    '50' => '.', # 'Z', 
    '7F' => 'v', # '0', 
    '88' => 'N', # '1', 
    'C5' => '\'', # '2', 
    'B7' => 'I', # '3', 
    'AB' => 'Y', # '4', 
    'CE' => 'W', # '5', 
    'AC' => 'O', # '6', 
    '9D' => 'T', # '7', 
  }
  count = Hash.new(0)
  encrypted_hex.split(/\s+/).each do |h|
    count[h] += 1
    g = guess[h]
    print g
  end
  puts
end

THECODE = <<"EOD"
78 AB DA 58 CB 0D 9C 9C 21 CB E4 2C CB 7D 9C F0
1C CB CE F0 BA 0D DA 24 21 78 CB 25 25 CB 4D 9C
CB 3F 1C DA 3F 3F 9C 7D CB 4D C2 0D CB BA 9C 0D
BA 25 BA 58 D3 9C CB C2 24 CB BA 4D 9C CB 1C F0
CD A9 21 CB F0 24 7D CB D3 9C 08 F0 24 CB BA DA
CB 97 9C CD BA 58 1C 9C CB 07 C2 BA 4D CB BA 4D
9C CB F0 C2 1C CB DA F9 CB F0 CB 3F 1C DA F9 9C
0D 0D DA 1C CB F0 7D 7D 1C 9C 0D 0D C2 24 08 CB
4D C2 0D CB CD 97 F0 0D 0D CB 25 25 CB 78 C2 BA
CB C2 0D CB 24 DA BA CB 1C 9C F0 97 97 2C CB 7D
C2 F9 F9 C2 CD 58 97 BA CB BA DA CB CD DA 24 0D
BA 1C 58 CD BA CB F0 CB 0D 9C 1C C2 9C 0D CB DA
F9 CB C2 24 F9 9C 1C 9C 24 CD 9C 0D 21 CB 9C F0
CD 4D CB 7D 9C 3F 9C 24 7D 9C 24 BA CB 58 3F DA
24 CB C2 BA 0D CB 3F 1C 9C 7D 9C CD 9C 0D 0D DA
1C CB F0 24 7D CB 9C F0 CD 4D CB 0D C2 E4 3F 97
9C CB C2 24 CB C2 BA 0D 9C 97 F9 50 CB CB B7 F9
21 CB F0 F9 BA 9C 1C CB 7D DA C2 24 08 CB 0D DA
21 CB DA 24 9C CB 0D C2 E4 3F 97 2C CB A9 24 DA
CD A9 0D CB DA 58 BA CB F0 97 97 CB BA 4D 9C CB
CD 9C 24 BA 1C F0 97 CB C2 24 F9 9C 1C 9C 24 CD
9C 0D CB F0 24 7D CB 3F 1C 9C 0D 9C 24 BA 0D CB
DA 24 9C C5 0D CB F0 58 7D C2 9C 24 CD 9C CB 07
C2 BA 4D CB BA 4D 9C CB 0D BA F0 1C BA C2 24 08
25 3F DA C2 24 BA CB F0 24 7D CB BA 4D 9C CB CD
DA 24 CD 97 58 0D C2 DA 24 21 CB DA 24 9C CB E4
F0 2C CB 3F 1C DA 7D 58 CD 9C CB F0 CB 0D BA F0
1C BA 97 C2 24 08 21 CB BA 4D DA 58 08 4D CB 3F
DA 0D 0D C2 D3 97 2C CB F0 CB E4 9C 1C 9C BA 1C
C2 CD C2 DA 58 0D 21 CB 9C F9 F9 9C CD BA 50 CB
88 DA 07 21 CB C2 BA CB 07 F0 0D CB 24 DA BA CB
1C 9C F0 97 97 2C CB 7D C2 F9 F9 C2 CD 58 97 BA
21 CB D3 2C CB F0 24 CB C2 24 0D 3F 9C CD BA C2
DA 24 CB DA F9 CB BA 4D 9C CB 08 1C DA DA 7F 9C
CB D3 9C BA 07 9C 9C 24 CB 2C DA 58 1C CB 97 9C
F9 BA CB F9 DA 1C 9C F9 C2 24 08 9C 1C CB F0 24
7D CB BA 4D 58 E4 D3 21 CB BA DA CB F9 9C 9C 97
CB 0D 58 1C 9C CB BA 4D F0 BA CB 2C DA 58 CB 7D
C2 7D CB 88 AC 9D CB 3F 1C DA 3F DA 0D 9C CB BA
DA CB C2 24 7F 9C 0D BA CB 2C DA 58 1C CB 0D E4
F0 97 97 CB CD F0 3F C2 BA F0 97 CB C2 24 CB BA
4D 9C CB 08 DA 97 7D CB F9 C2 9C 97 7D 0D 50 78
EOD

analyze(THECODE)

analyze2.rb

require 'digest'

THECODE =<<"EOD"
C8 EE A8 0F 80 FD 60 E9 00 3F C4 B0 10 2C E7 33
DC 82 1E 6B D3 5B BB FA 8A 48 C2 F0 97 7F A6 C0
9C 32 15 89 37 51 AA C9 D8 93 9D 86 DA 28 BB 58
A2 6D E2 7F 3A 3B A5 F1 A5 31 89 6C D8 B5 E6 15
EOD

(0..255).each do |seed|
  printf("seed = %02X", seed)
  sha = Digest::SHA1.new
  decoded_text = ''
  THECODE.split(/\s+/).each do |cc|
    code = cc.hex
    decoded = code ^ seed
    if (decoded >= 0x7f) or (decoded < 0x20 and decoded != 0x09)
      break
    else
      decoded_text += decoded.chr
    end
    sha.update(seed.chr)
    seed = sha.digest.split(//)[19].ord
  end
  if decoded_text.length > 10
    printf(", decoded_text = %s...\n", decoded_text)
  else
    puts
  end
end

cryptan1.rb

#!/usr/bin/ruby

def cipher(plain_text, seed, mode = :encrypt)
  rng = Random.new(seed)
  sbox = (0..255).to_a.shuffle(random: rng)
  if mode == :decrypt
    rbox = []
    sbox.each_with_index { |n,i| rbox[n] = i }
    sbox = rbox
  end
  encrypted_text = ''
  plain_text.split(//).each do |c|
    plain = c.ord
    encrypted = sbox[plain]
    printf("%02X -> %02X (seed = %02X)\n", plain, encrypted, seed) if $DEBUG
    encrypted_text += encrypted.chr
  end
  encrypted_text
end

def encrypt_tohex(plain_text, seed)
  hex = ''
  cipher(plain_text, seed).split(//).each_with_index do |c,i|
    hex += sprintf("%02X", c.ord)
    if i % 16 == 15
      hex += "\n"
    else
      hex += " "
    end
  end
  hex += "\n"
  hex
end

def decrypt_fromhex(encrypted_hex, seed)
  encrypted_text = ''
  encrypted_hex.split(/\s+/).each do |h|
    encrypted_text += h.hex.chr
  end
  cipher(encrypted_text, seed, :decrypt)
end

PLAIN_TEXT = %Q("You see, my dear Watson," -- he propped his test-tube in the rack, and began to lecture with the air of a professor addressing his class -- "it is not really difficult to construct a series of inferences, each dependent upon its predecessor and each simple in itself.  If, after doing so, one simply knocks out all the central inferences and presents one's audience with the starting-point and the conclusion, one may produce a startling, though possibly a meretricious, effect. Now, it was not really difficult, by an inspection of the groove between your left forefinger and thumb, to feel sure that you did NOT propose to invest your small capital in the gold fields.")

print encrypt_tohex(PLAIN_TEXT, 123)

THECODE = <<"EOD"
78 AB DA 58 CB 0D 9C 9C 21 CB E4 2C CB 7D 9C F0
1C CB CE F0 BA 0D DA 24 21 78 CB 25 25 CB 4D 9C
CB 3F 1C DA 3F 3F 9C 7D CB 4D C2 0D CB BA 9C 0D
BA 25 BA 58 D3 9C CB C2 24 CB BA 4D 9C CB 1C F0
CD A9 21 CB F0 24 7D CB D3 9C 08 F0 24 CB BA DA
CB 97 9C CD BA 58 1C 9C CB 07 C2 BA 4D CB BA 4D
9C CB F0 C2 1C CB DA F9 CB F0 CB 3F 1C DA F9 9C
0D 0D DA 1C CB F0 7D 7D 1C 9C 0D 0D C2 24 08 CB
4D C2 0D CB CD 97 F0 0D 0D CB 25 25 CB 78 C2 BA
CB C2 0D CB 24 DA BA CB 1C 9C F0 97 97 2C CB 7D
C2 F9 F9 C2 CD 58 97 BA CB BA DA CB CD DA 24 0D
BA 1C 58 CD BA CB F0 CB 0D 9C 1C C2 9C 0D CB DA
F9 CB C2 24 F9 9C 1C 9C 24 CD 9C 0D 21 CB 9C F0
CD 4D CB 7D 9C 3F 9C 24 7D 9C 24 BA CB 58 3F DA
24 CB C2 BA 0D CB 3F 1C 9C 7D 9C CD 9C 0D 0D DA
1C CB F0 24 7D CB 9C F0 CD 4D CB 0D C2 E4 3F 97
9C CB C2 24 CB C2 BA 0D 9C 97 F9 50 CB CB B7 F9
21 CB F0 F9 BA 9C 1C CB 7D DA C2 24 08 CB 0D DA
21 CB DA 24 9C CB 0D C2 E4 3F 97 2C CB A9 24 DA
CD A9 0D CB DA 58 BA CB F0 97 97 CB BA 4D 9C CB
CD 9C 24 BA 1C F0 97 CB C2 24 F9 9C 1C 9C 24 CD
9C 0D CB F0 24 7D CB 3F 1C 9C 0D 9C 24 BA 0D CB
DA 24 9C C5 0D CB F0 58 7D C2 9C 24 CD 9C CB 07
C2 BA 4D CB BA 4D 9C CB 0D BA F0 1C BA C2 24 08
25 3F DA C2 24 BA CB F0 24 7D CB BA 4D 9C CB CD
DA 24 CD 97 58 0D C2 DA 24 21 CB DA 24 9C CB E4
F0 2C CB 3F 1C DA 7D 58 CD 9C CB F0 CB 0D BA F0
1C BA 97 C2 24 08 21 CB BA 4D DA 58 08 4D CB 3F
DA 0D 0D C2 D3 97 2C CB F0 CB E4 9C 1C 9C BA 1C
C2 CD C2 DA 58 0D 21 CB 9C F9 F9 9C CD BA 50 CB
88 DA 07 21 CB C2 BA CB 07 F0 0D CB 24 DA BA CB
1C 9C F0 97 97 2C CB 7D C2 F9 F9 C2 CD 58 97 BA
21 CB D3 2C CB F0 24 CB C2 24 0D 3F 9C CD BA C2
DA 24 CB DA F9 CB BA 4D 9C CB 08 1C DA DA 7F 9C
CB D3 9C BA 07 9C 9C 24 CB 2C DA 58 1C CB 97 9C
F9 BA CB F9 DA 1C 9C F9 C2 24 08 9C 1C CB F0 24
7D CB BA 4D 58 E4 D3 21 CB BA DA CB F9 9C 9C 97
CB 0D 58 1C 9C CB BA 4D F0 BA CB 2C DA 58 CB 7D
C2 7D CB 88 AC 9D CB 3F 1C DA 3F DA 0D 9C CB BA
DA CB C2 24 7F 9C 0D BA CB 2C DA 58 1C CB 0D E4
F0 97 97 CB CD F0 3F C2 BA F0 97 CB C2 24 CB BA
4D 9C CB 08 DA 97 7D CB F9 C2 9C 97 7D 0D 50 78
EOD

puts decrypt_fromhex(THECODE, 123)

cryptan2.rb

#!/usr/bin/ruby

require 'digest'

def cipher(plain_text, seed)
  encrypted_text = ''
  seed = seed % 256
  sha1 = Digest::SHA1.new
  plain_text.split(//).each do |c|
    plain = c.ord
    encrypted = plain ^ seed
    printf("%02X -> %02X (seed = %02X)\n", plain, encrypted, seed) if $DEBUG
    encrypted_text += encrypted.chr
    sha1.update(seed.chr)
    seed = sha1.digest.split(//)[19].ord
  end
  encrypted_text
end

def encrypt_tohex(plain_text, seed)
  hex = ''
  cipher(plain_text, seed).split(//).each_with_index do |c,i|
    hex += sprintf("%02X", c.ord)
    if i % 16 == 15
      hex += "\n"
    else
      hex += " "
    end
  end
  hex += "\n"
  hex
end

def decrypt_fromhex(encrypted_hex, seed)
  encrypted_text = ''
  encrypted_hex.split(/\s+/).each do |h|
    encrypted_text += h.hex.chr
  end
  cipher(encrypted_text, seed)
end

PLAIN_TEXT = %Q("If you use the code which I have explained," said Holmes,"you will find that it simply means 'Come here at once.' I was convinced that it was an invitation which he would not refuse, since he could never imagine that it could come from anyone but the lady. And so, my dear Watson, we have ended by turning the dancing men to good when they have so often been the agents of evil, and I think that I have fulfilled my promise of giving you something unusual for your notebook. Three-forty is our train, and I fancy we should be back in Baker Street for dinner.")

print encrypt_tohex(PLAIN_TEXT, 234)

THECODE = <<"EOD"
C8 EE A8 0F 80 FD 60 E9 00 3F C4 B0 10 2C E7 33
DC 82 1E 6B D3 5B BB FA 8A 48 C2 F0 97 7F A6 C0
9C 32 15 89 37 51 AA C9 D8 93 9D 86 DA 28 BB 58
A2 6D E2 7F 3A 3B A5 F1 A5 31 89 6C D8 B5 E6 15
BC A4 BC 59 93 CD 68 85 52 48 93 36 B1 F4 5E FA
D1 62 7C 4B C1 A2 E4 98 7F 17 D5 21 37 7F C5 A0
2C BE 67 4D DC 5A 0B 66 D9 D4 5B 09 58 2F 72 ED
4F 45 81 36 73 AB 18 DF 51 5C 1A D3 7F 2E EF B8
D8 C8 C0 8A 4C BA 87 23 01 44 46 E7 03 42 EF 44
EA 05 36 11 3C 03 67 24 A4 BC 53 EF 6E 2D C3 66
B9 CF 9C C2 55 04 9C F8 F4 99 B8 AF FF EA 16 7D
AA EC FF 7D E2 52 8B B7 65 EE 2C 69 07 1D D9 14
C5 5A 6B 5A BC EF 34 12 C4 0D 7D 4E AA DD 19 0A
2B 5F 8B CE 06 2D A0 6C 76 49 E2 62 AC 4B 04 46
FA E6 58 3E D0 7B 58 F0 8A 9E 67 1B 96 3C B3 93
94 66 8A 44 50 D5 4F F8 49 33 4E BA CA E1 95 24
92 43 85 FC A8 B1 66 6F 46 57 BD A5 B3 1E 1B 47
5B 95 EB E7 8C 41 25 DC 88 9D 66 72 36 6B C1 D8
E8 60 59 BA 1F BD 66 A7 3C A3 1D 08 DE CF EB 02
10 90 FD 9A F9 51 83 6C 22 79 6F 79 D7 98 52 43
DD 1E 66 AB E1 F0 E2 E4 85 0D 5F E5 B9 83 07 E0
84 9C B8 3A 60 1E 00 31 8B E9 7B 9B 6E 56 F0 84
81 A7 AE AE BE B2 56 0A C3 B8 DE B8 5C 8A 09 83
4C 9F 12 D3 DE C2 08 F2 79 CF 71 51 B3 E5 F0 D2
47 12 0E DF 98 B2 5C 02 E7 E3 4D B3 6B 20 91 0D
7C 0E E2 95 2E 7A 29 E2 7C C0 A8 9A B6 25 C1 FB
E5 EB A5 A0 F6 E2 E6 A0 70 4E E5 8F DE 1E 9C 33
29 2F DA 85 E0 9A C2 F6 6F 71 A9 84 E7 F9 61 29
50 3A 0A 65 C3 BD 91 CC 7E 52 69 84 12 27 6C 97
0C 9C FC 60 32 58 7D BD 2E 4F 5A 36 97 ED 34 5A
35 2F A8 ED DC A0 67 F0 FE 17 C9 E0 6E D6 D1 9D
58 C2 E0 81 6F C1 7F E9 38 5C EC 5A 30 08 00 CB
C3 65 2F A9 78 6D F5 C0 D1 34 8E 99 C8 52 85 E4
F7 06 FD E7 1B 14 9F 97 BD D9 97 29 18 8A 2A E4
76 AA 36 2D CE 4E E4 D0 84 69 65 22 0C 9B A4 42
EOD

# (0..255).each do |key|
#   puts "#{key} : " + decrypt_fromhex(THECODE, key)
# end

puts decrypt_fromhex(THECODE, 234)