coffeejunk/crypt19

# coding: ASCII
# adapted from C++ code written by Wei Dai
# of the Crypto++ project http://www.eskimo.com/~weidai/cryptlib.html

require 'crypt/cbc'
require 'crypt/block_methods'

module Crypt
  class Gost

    include CBC

    include BlockMethods

    ULONG   = 0x100000000

    def block_size
      return(8)
    end


    def initialize(user_key)

      # These are the S-boxes given in Applied Cryptography 2nd Ed., p. 333
      @sBox = [
        [4, 10, 9, 2, 13, 8, 0, 14, 6, 11, 1, 12, 7, 15, 5, 3],
        [14, 11, 4, 12, 6, 13, 15, 10, 2, 3, 8, 1, 0, 7, 5, 9],
        [5, 8, 1, 13, 10, 3, 4, 2, 14, 15, 12, 7, 6, 0, 9, 11],
        [7, 13, 10, 1, 0, 8, 9, 15, 14, 4, 6, 12, 11, 2, 5, 3],
        [6, 12, 7, 1, 5, 15, 13, 8, 4, 10, 9, 14, 0, 3, 11, 2],
        [4, 11, 10, 0, 7, 2, 1, 13, 3, 6, 8, 5, 9, 12, 15, 14],
        [13, 11, 4, 1, 3, 15, 5, 9, 0, 10, 14, 7, 6, 8, 2, 12],
        [1, 15, 13, 0, 5, 7, 10, 4, 9, 2, 3, 14, 6, 11, 8, 12]
      ]

      # These are the S-boxes given in the GOST source code listing in Applied
        # Cryptography 2nd Ed., p. 644.  They appear to be from the DES S-boxes
      # [13,  2,  8,  4,  6, 15, 11,  1, 10,  9,  3, 14,  5,  0, 12,  7 ],
      # [ 4, 11,  2, 14, 15,  0,  8, 13,  3, 12,  9,  7,  5, 10,  6,  1 ],
      # [12,  1, 10, 15,  9,  2,  6,  8,  0, 13,  3,  4, 14,  7,  5, 11 ],
      # [ 2, 12,  4,  1,  7, 10, 11,  6,  8,  5,  3, 15, 13,  0, 14,  9 ],
      # [ 7, 13, 14,  3,  0,  6,  9, 10,  1,  2,  8,  5, 11, 12,  4, 15 ],
      # [10,  0,  9, 14,  6,  3, 15,  5,  1, 13, 12,  7, 11,  4,  2,  8 ],
      # [15,  1,  8, 14,  6, 11,  3,  4,  9,  7,  2, 13, 12,  0,  5, 10 ],
      # [14,  4, 13,  1,  2, 15, 11,  8,  3, 10,  6, 12,  5,  9,  0,  7 ]

      # precalculate the S table
      @s_table = precalculate_s_table()

      # derive the 32-byte key from the user-supplied key
      user_key_length = user_key.length
      @key = user_key[0..31].unpack('C'*32)
      if (user_key_length < 32)
        user_key_length.upto(31) { @key << 0 }
      end
    end


    def precalculate_s_table()
      s_table = [[], [], [], []]
      0.upto(3) { |i|
        0.upto(255) { |j|
          t = @sBox[2*i][j % 16] | (@sBox[2*i+1][j/16] << 4)
          u = (8*i + 11) % 32
          v = (t << u) | (t >> (32-u))
          s_table[i][j] = (v % ULONG)
        }
      }
      return(s_table)
    end


    def f(long_word)
      long_word = long_word % ULONG
      a, b, c, d = [long_word].pack('L').unpack('CCCC')
      return(@s_table[3][d] ^ @s_table[2][c] ^ @s_table[1][b] ^ @s_table[0][a])
    end


    def encrypt_pair(xl, xr)
      3.times {
        xr ^= f(xl+@key[0])
        xl ^= f(xr+@key[1])
        xr ^= f(xl+@key[2])
        xl ^= f(xr+@key[3])
        xr ^= f(xl+@key[4])
        xl ^= f(xr+@key[5])
        xr ^= f(xl+@key[6])
        xl ^= f(xr+@key[7])
      }
      xr ^= f(xl+@key[7])
      xl ^= f(xr+@key[6])
      xr ^= f(xl+@key[5])
      xl ^= f(xr+@key[4])
      xr ^= f(xl+@key[3])
      xl ^= f(xr+@key[2])
      xr ^= f(xl+@key[1])
      xl ^= f(xr+@key[0])
      return([xr, xl])
    end


    def decrypt_pair(xl, xr)
      xr ^= f(xl+@key[0])
      xl ^= f(xr+@key[1])
      xr ^= f(xl+@key[2])
      xl ^= f(xr+@key[3])
      xr ^= f(xl+@key[4])
      xl ^= f(xr+@key[5])
      xr ^= f(xl+@key[6])
      xl ^= f(xr+@key[7])
      3.times {
        xr ^= f(xl+@key[7])
        xl ^= f(xr+@key[6])
        xr ^= f(xl+@key[5])
        xl ^= f(xr+@key[4])
        xr ^= f(xl+@key[3])
        xl ^= f(xr+@key[2])
        xr ^= f(xl+@key[1])
        xl ^= f(xr+@key[0])
      }
      return([xr, xl])
    end

  end
end