Module: Net::SSH::Transport::CTR

Defined in:
lib/net/ssh/transport/ctr.rb

Overview

:nodoc: Pure-Ruby implementation of Stateful Decryption Counter(SDCTR) Mode for Block Ciphers. See RFC4344 for detail.

Class Method Summary collapse

Class Method Details

.extended(orig) ⇒ Object 



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# File 'lib/net/ssh/transport/ctr.rb', line 33

def self.extended(orig)
  orig.instance_eval {
    @remaining = String.new
    @counter = nil
    @counter_len = orig.block_size
    orig.encrypt
    orig.padding = 0

    singleton_class.send(:alias_method, :_update, :update)
    singleton_class.send(:private, :_update)
    singleton_class.send(:undef_method, :update)

    def iv
      @counter
    end

    def iv_len
      block_size
    end

    def iv=(iv_s)
      @counter = iv_s if @counter.nil?
    end

    def encrypt
      # DO NOTHING (always set to "encrypt")
    end

    def decrypt
      # DO NOTHING (always set to "encrypt")
    end

    def padding=(pad)
      # DO NOTHING (always 0)
    end

    def reset
      @remaining = String.new
    end

    def update(data)
      @remaining += data

      encrypted = String.new

      offset = 0
      while (@remaining.bytesize - offset) >= block_size
        encrypted += xor!(@remaining.slice(offset, block_size),
                          _update(@counter))
        increment_counter!
        offset += block_size
      end
      @remaining = @remaining.slice(offset..-1)

      encrypted
    end

    def final
      s = @remaining.empty? ? '' : xor!(@remaining, _update(@counter))
      @remaining = String.new
      s
    end

    def xor!(s1, s2)
      s = []
      s1.unpack('Q*').zip(s2.unpack('Q*')) {|a, b| s.push(a ^ b) }
      s.pack('Q*')
    end
    singleton_class.send(:private, :xor!)

    def increment_counter!
      c = @counter_len
      while ((c -= 1) > 0)
        if @counter.setbyte(c, (@counter.getbyte(c) + 1) & 0xff) != 0
          break
        end
      end
    end
    singleton_class.send(:private, :increment_counter!)
  }
end