Module: Feistel

Defined in:
lib/ruby-des/feistel.rb

Constant Summary collapse

E = 
[0x20, 0x01, 0x02, 0x03, 0x04, 0x05,
0x04, 0x05, 0x06, 0x07, 0x08, 0x09,
0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d,
0x0c, 0x0d, 0x0e, 0x0f, 0x10, 0x11,
0x10, 0x11, 0x12, 0x13, 0x14, 0x15,
0x14, 0x15, 0x16, 0x17, 0x18, 0x19,
0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d,
0x1c, 0x1d, 0x1e, 0x1f, 0x20, 0x01]
P = 
[0x10, 0x07, 0x14, 0x15,
0x1d, 0x0c, 0x1c, 0x11,
0x01, 0x0f, 0x17, 0x1a,
0x05, 0x12, 0x1f, 0x0a,
0x02, 0x08, 0x18, 0x0e,
0x20, 0x1b, 0x03, 0x09,
0x13, 0x0d, 0x1e, 0x06,
0x16, 0x0b, 0x04, 0x19]
S1 = 
[0x0e, 0x04, 0x0d, 0x01, 0x02, 0x0f, 0x0b, 0x08, 0x03, 0x0a, 0x06, 0x0c, 0x05, 0x09, 0x00, 0x07,
0x00, 0x0f, 0x07, 0x04, 0x0e, 0x02, 0x0d, 0x01, 0x0a, 0x06, 0x0c, 0x0b, 0x09, 0x05, 0x03, 0x08,
0x04, 0x01, 0x0e, 0x08, 0x0d, 0x06, 0x02, 0x0b, 0x0f, 0x0c, 0x09, 0x07, 0x03, 0x0a, 0x05, 0x00,
0x0f, 0x0c, 0x08, 0x02, 0x04, 0x09, 0x01, 0x07, 0x05, 0x0b, 0x03, 0x0e, 0x0a, 0x00, 0x06, 0x0d]
S2 = 
[0x0f, 0x01, 0x08, 0x0e, 0x06, 0x0b, 0x03, 0x04, 0x09, 0x07, 0x02, 0x0d, 0x0c, 0x00, 0x05, 0x0a,
0x03, 0x0d, 0x04, 0x07, 0x0f, 0x02, 0x08, 0x0e, 0x0c, 0x00, 0x01, 0x0a, 0x06, 0x09, 0x0b, 0x05,
0x00, 0x0e, 0x07, 0x0b, 0x0a, 0x04, 0x0d, 0x01, 0x05, 0x08, 0x0c, 0x06, 0x09, 0x03, 0x02, 0x0f,
0x0d, 0x08, 0x0a, 0x01, 0x03, 0x0f, 0x04, 0x02, 0x0b, 0x06, 0x07, 0x0c, 0x00, 0x05, 0x0e, 0x09]
S3 = 
[0x0a, 0x00, 0x09, 0x0e, 0x06, 0x03, 0x0f, 0x05, 0x01, 0x0d, 0x0c, 0x07, 0x0b, 0x04, 0x02, 0x08,
0x0d, 0x07, 0x00, 0x09, 0x03, 0x04, 0x06, 0x0a, 0x02, 0x08, 0x05, 0x0e, 0x0c, 0x0b, 0x0f, 0x01,
0x0d, 0x06, 0x04, 0x09, 0x08, 0x0f, 0x03, 0x00, 0x0b, 0x01, 0x02, 0x0c, 0x05, 0x0a, 0x0e, 0x07,
0x01, 0x0a, 0x0d, 0x00, 0x06, 0x09, 0x08, 0x07, 0x04, 0x0f, 0x0e, 0x03, 0x0b, 0x05, 0x02, 0x0c]
S4 = 
[0x07, 0x0d, 0x0e, 0x03, 0x00, 0x06, 0x09, 0x0a, 0x01, 0x02, 0x08, 0x05, 0x0b, 0x0c, 0x04, 0x0f,
0x0d, 0x08, 0x0b, 0x05, 0x06, 0x0f, 0x00, 0x03, 0x04, 0x07, 0x02, 0x0c, 0x01, 0x0a, 0x0e, 0x09,
0x0a, 0x06, 0x09, 0x00, 0x0c, 0x0b, 0x07, 0x0d, 0x0f, 0x01, 0x03, 0x0e, 0x05, 0x02, 0x08, 0x04,
0x03, 0x0f, 0x00, 0x06, 0x0a, 0x01, 0x0d, 0x08, 0x09, 0x04, 0x05, 0x0b, 0x0c, 0x07, 0x02, 0x0e]
S5 = 
[0x02, 0x0c, 0x04, 0x01, 0x07, 0x0a, 0x0b, 0x06, 0x08, 0x05, 0x03, 0x0f, 0x0d, 0x00, 0x0e, 0x09,
0x0e, 0x0b, 0x02, 0x0c, 0x04, 0x07, 0x0d, 0x01, 0x05, 0x00, 0x0f, 0x0a, 0x03, 0x09, 0x08, 0x06,
0x04, 0x02, 0x01, 0x0b, 0x0a, 0x0d, 0x07, 0x08, 0x0f, 0x09, 0x0c, 0x05, 0x06, 0x03, 0x00, 0x0e,
0x0b, 0x08, 0x0c, 0x07, 0x01, 0x0e, 0x02, 0x0d, 0x06, 0x0f, 0x00, 0x09, 0x0a, 0x04, 0x05, 0x03]
S6 = 
[0x0c, 0x01, 0x0a, 0x0f, 0x09, 0x02, 0x06, 0x08, 0x00, 0x0d, 0x03, 0x04, 0x0e, 0x07, 0x05, 0x0b,
0x0a, 0x0f, 0x04, 0x02, 0x07, 0x0c, 0x09, 0x05, 0x06, 0x01, 0x0d, 0x0e, 0x00, 0x0b, 0x03, 0x08,
0x09, 0x0e, 0x0f, 0x05, 0x02, 0x08, 0x0c, 0x03, 0x07, 0x00, 0x04, 0x0a, 0x01, 0x0d, 0x0b, 0x06,
0x04, 0x03, 0x02, 0x0c, 0x09, 0x05, 0x0f, 0x0a, 0x0b, 0x0e, 0x01, 0x07, 0x06, 0x00, 0x08, 0x0d]
S7 = 
[0x04, 0x0b, 0x02, 0x0e, 0x0f, 0x00, 0x08, 0x0d, 0x03, 0x0c, 0x09, 0x07, 0x05, 0x0a, 0x06, 0x01,
0x0d, 0x00, 0x0b, 0x07, 0x04, 0x09, 0x01, 0x0a, 0x0e, 0x03, 0x05, 0x0c, 0x02, 0x0f, 0x08, 0x06,
0x01, 0x04, 0x0b, 0x0d, 0x0c, 0x03, 0x07, 0x0e, 0x0a, 0x0f, 0x06, 0x08, 0x00, 0x05, 0x09, 0x02,
0x06, 0x0b, 0x0d, 0x08, 0x01, 0x04, 0x0a, 0x07, 0x09, 0x05, 0x00, 0x0f, 0x0e, 0x02, 0x03, 0x0c]
S8 = 
[0x0d, 0x02, 0x08, 0x04, 0x06, 0x0f, 0x0b, 0x01, 0x0a, 0x09, 0x03, 0x0e, 0x05, 0x00, 0x0c, 0x07,
0x01, 0x0f, 0x0d, 0x08, 0x0a, 0x03, 0x07, 0x04, 0x0c, 0x05, 0x06, 0x0b, 0x00, 0x0e, 0x09, 0x02,
0x07, 0x0b, 0x04, 0x01, 0x09, 0x0c, 0x0e, 0x02, 0x00, 0x06, 0x0a, 0x0d, 0x0f, 0x03, 0x05, 0x08,
0x02, 0x01, 0x0e, 0x07, 0x04, 0x0a, 0x08, 0x0d, 0x0f, 0x0c, 0x09, 0x00, 0x03, 0x05, 0x06, 0x0b]
S = 
[S1, S2, S3, S4, S5, S6, S7, S8]

Class Method Summary collapse

Class Method Details

.run(r, k) ⇒ Object 



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# File 'lib/ruby-des/feistel.rb', line 62

def self.run(r, k)    
  b = [] # b[0..7] is e_xor_k prepped as 8 6-bit arrays for s-box substitution.
  m = [] # m[0..7] is the row of the value when performing a s-box lookup.
  n = [] # n[0..7] is the column of the value when performing a s-box lookup.
  
  e = E.collect{|p| r[p - 1]} # Expand r (right half data block) using E.
  
  e_xor_k = XOR.run(e, k) # X-or e (expanded r) with k (the sub key).
  
  # Break e_xor_k into 8 6-bit arrays and find both m (s-box row) and n (s-box column) for the s-box lookup.
  8.times do |i|
    b << []
      6.times do 
      b[i] << e_xor_k.shift
    end
    
    m << [b[i].first, b[i].last].join.to_i(2) * 16 # [1, 0, 1, 0, 1, 0] => [1, 0] => 2 => 32 => 3rd row.
    n << b[i][1..4].join.to_i(2) # [1, 0, 1, 0, 1, 0] => [0, 1, 0, 1] => 5 => 6th column.
  end
  
  # Substitute every 6-bit array with the 4-bit array specified by the appropriate s-box.
  8.times do |i|
      b[i] = S[i][m[i] + n[i]].to_s(2).rjust(4, '0').split('').collect{|bit| bit.to_i}
  end
      
  return P.collect{|p| b.flatten[p - 1]}
end