gistfile1.rb

# CFB ENCRYPT
# 1. przygotować IV do ECB
# 2. zaszyfrować IV w trybie ECB

# 3. zabrać z wyjścia (2) z ECB [feedbackSize] bajtów z początku
# 4. StringXor [feedbackSize] bajtów wejścia z [feedbackSize] bajtami wyjścia ECB
# 5. Efekt (4) dodać do szyfrogramu
# 6. Efekt (4) wstawić na koniec IV do ECB z (1)
# 7. Usunąć [feedbackSize] bajtów z -początku- IV do ECB z (1)

require 'openssl'

input = 'abcdefghijklmnopqrstuwvxyz'


puts 'RUBY :: CFB from ECB'
puts '      IN: ' + input.bytesize.to_s + ' :: ' + input

for feedbackSize in 1..8
  c = OpenSSL::Cipher.new('bf-ecb')
  c.encrypt
  c.key = '1234567890123456'
  block = '00000000'
  enc = c.update(block);
  out = ''
  pos = 0
  # LOOP
  while block = input.byteslice(pos, feedbackSize)
    pos += feedbackSize
    feedback = enc.byteslice(0, feedbackSize) # 3
    enc = enc.byteslice(feedbackSize..8) # 7
    sub = (block ^ feedback) # 4
    out += sub # 5
    block = enc + sub # 6
    enc = c.update(block); # 2!!
  
  end
  # ENDLOOP
  
  puts ' CFB OUT: ' + out.bytesize.to_s + ' :: ' + out.unpack('h*')[0] + ' :: feedbackSize: ' + feedbackSize.to_s
  
end