Class: Crypt::Gost

Inherits:
Object
  • Object
show all
Includes:
CBC
Defined in:
lib/crypt/gost.rb

Overview

of the Crypto++ project www.eskimo.com/~weidai/cryptlib.html

Constant Summary collapse

ULONG = 
0x100000000

Instance Method Summary collapse

Methods included from CBC

#carefully_open_file, #decrypt_file, #decrypt_stream, #decrypt_string, #encrypt_file, #encrypt_stream, #encrypt_string, #generate_initialization_vector

Constructor Details

#initialize(userKey) ⇒ Gost

Returns a new instance of Gost.



18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
 
# File 'lib/crypt/gost.rb', line 18

def initialize(userKey)

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

Instance Method Details

#block_size ⇒ Object 



13
14
15
 
# File 'lib/crypt/gost.rb', line 13

def block_size
  return(8)
end

#decrypt_block(block) ⇒ Object 



130
131
132
133
134
135
 
# File 'lib/crypt/gost.rb', line 130

def decrypt_block(block)
  xl, xr = block.unpack('NN')
  xl, xr = decrypt_pair(xl, xr)
  decrypted = [xl, xr].pack('NN')
  return(decrypted)
end

#decrypt_pair(xl, xr) ⇒ Object 



99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
 
# File 'lib/crypt/gost.rb', line 99

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

#encrypt_block(block) ⇒ Object 



122
123
124
125
126
127
 
# File 'lib/crypt/gost.rb', line 122

def encrypt_block(block)
  xl, xr = block.unpack('NN')
  xl, xr = encrypt_pair(xl, xr)
  encrypted = [xl, xr].pack('NN')
  return(encrypted)
end

#encrypt_pair(xl, xr) ⇒ Object 



76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
 
# File 'lib/crypt/gost.rb', line 76

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

#f(longWord) ⇒ Object 



69
70
71
72
73
 
# File 'lib/crypt/gost.rb', line 69

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

#precalculate_S_table ⇒ Object 



55
56
57
58
59
60
61
62
63
64
65
66
 
# File 'lib/crypt/gost.rb', line 55

def precalculate_S_table()
  sTable = [[], [], [], []]
  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))
      sTable[i][j] = (v % ULONG)
    } 
  }
  return(sTable)
end