Module: Aes

Defined in:
lib/aesctr-ruby.rb

Class Method Summary collapse

Class Method Details

.cipher(input, w) ⇒ Object

AES Cipher function: encrypt ‘input’ state with Rijndael algorithm applies Nr rounds (10/12/14) using key schedule w for ‘add round key’ stage

Parameters:

  • int[] —

    input 16-byte (128-bit) input state array

  • int[][] —

    w Key schedule as 2D byte-array (Nr+1 x Nb bytes)



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# File 'lib/aesctr-ruby.rb', line 46

def self.cipher(input, w) #main Cipher function [§5.1]
  nb = 4;             #block size (in words): no of columns in state (fixed at 4 for AES)
  nr = w.length/nb -1 ## no of rounds: 10/12/14 for 128/192/256-bit keys
  state = [[],[],[],[]]  # initialise 4xNb byte-array 'state' with input [§3.4]

  (0...(4*nb)).each do |i|
      state[i%4][(i/4.0).floor] = input[i]
  end
  state = self.addRoundKey(state,w,0,nb)
  (1...nr).each do |round|
     state = Aes.subBytes(state, nb)
     state = Aes.shiftRows(state, nb)
     state = Aes.mixColumns(state, nb)
     state = Aes.addRoundKey(state, w,round,nb)
  end
  state = Aes.subBytes(state, nb)
  state = Aes.shiftRows(state, nb)
  state = Aes.addRoundKey(state, w, nr,nb)

  output = []
  (0...(4*nb)).each{|i| output[i] = state[i%4][(i/4.0).floor]}
  output
end

.keyExpansion(key) ⇒ Object

Perform Key Expansion to generate a Key Schedule

@param int[] key Key as 16/24/32-byte array
@returns int[][] Expanded key schedule as 2D byte-array (Nr+1 x Nb bytes)



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# File 'lib/aesctr-ruby.rb', line 74

def self.keyExpansion(key)
  nb = 4              # block size (in words): no of columns in state (fixed at 4 for AES)
  nk = key.length/4   # key length (in words): 4/6/8 for 128/192/256-bit keys
  nr = nk + 6         # no of rounds: 10/12/14 for 128/192/256-bit keys

  w = []
  temp = []
  0.upto(nk-1){|i| w[i] = [key[4*i], key[4*i+1], key[4*i+2], key[4*i+3]] }
  (nk...(nb*(nr+1))).each do |i|
    w[i] = []
    0.upto(3){|t| temp[t] = w[i-1][t]}
    if(i % nk == 0)
      temp = self.subWord(self.rotWord(temp))
      0.upto(3){|t| temp[t] ^= self.rCon[i/nk][t]}
    elsif(nk > 6 && i%nk==4)
        temp = self.subWord(temp)
    end
    0.upto(3){|t| w[i][t] = w[i-nk][t] ^ temp[t] }
  end
  w
end

.rCon ⇒ Object

rCon is Round Constant used for the Key Expansion [1st col is 2^(r-1) in GF(2^8)] [§5.2]



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# File 'lib/aesctr-ruby.rb', line 25

def self.rCon
         [ [0x00, 0x00, 0x00, 0x00],
           [0x01, 0x00, 0x00, 0x00],
           [0x02, 0x00, 0x00, 0x00],
           [0x04, 0x00, 0x00, 0x00],
           [0x08, 0x00, 0x00, 0x00],
           [0x10, 0x00, 0x00, 0x00],
           [0x20, 0x00, 0x00, 0x00],
           [0x40, 0x00, 0x00, 0x00],
           [0x80, 0x00, 0x00, 0x00],
           [0x1b, 0x00, 0x00, 0x00],
           [0x36, 0x00, 0x00, 0x00] ]
end

.sBox ⇒ Object

sBox is pre-computed multiplicative inverse in GF(2^8) used in subBytes and keyExpansion [§5.1.1]



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# File 'lib/aesctr-ruby.rb', line 5

def self.sBox
          [0x63,0x7c,0x77,0x7b,0xf2,0x6b,0x6f,0xc5,0x30,0x01,0x67,0x2b,0xfe,0xd7,0xab,0x76,
           0xca,0x82,0xc9,0x7d,0xfa,0x59,0x47,0xf0,0xad,0xd4,0xa2,0xaf,0x9c,0xa4,0x72,0xc0,
           0xb7,0xfd,0x93,0x26,0x36,0x3f,0xf7,0xcc,0x34,0xa5,0xe5,0xf1,0x71,0xd8,0x31,0x15,
           0x04,0xc7,0x23,0xc3,0x18,0x96,0x05,0x9a,0x07,0x12,0x80,0xe2,0xeb,0x27,0xb2,0x75,
           0x09,0x83,0x2c,0x1a,0x1b,0x6e,0x5a,0xa0,0x52,0x3b,0xd6,0xb3,0x29,0xe3,0x2f,0x84,
           0x53,0xd1,0x00,0xed,0x20,0xfc,0xb1,0x5b,0x6a,0xcb,0xbe,0x39,0x4a,0x4c,0x58,0xcf,
           0xd0,0xef,0xaa,0xfb,0x43,0x4d,0x33,0x85,0x45,0xf9,0x02,0x7f,0x50,0x3c,0x9f,0xa8,
           0x51,0xa3,0x40,0x8f,0x92,0x9d,0x38,0xf5,0xbc,0xb6,0xda,0x21,0x10,0xff,0xf3,0xd2,
           0xcd,0x0c,0x13,0xec,0x5f,0x97,0x44,0x17,0xc4,0xa7,0x7e,0x3d,0x64,0x5d,0x19,0x73,
           0x60,0x81,0x4f,0xdc,0x22,0x2a,0x90,0x88,0x46,0xee,0xb8,0x14,0xde,0x5e,0x0b,0xdb,
           0xe0,0x32,0x3a,0x0a,0x49,0x06,0x24,0x5c,0xc2,0xd3,0xac,0x62,0x91,0x95,0xe4,0x79,
           0xe7,0xc8,0x37,0x6d,0x8d,0xd5,0x4e,0xa9,0x6c,0x56,0xf4,0xea,0x65,0x7a,0xae,0x08,
           0xba,0x78,0x25,0x2e,0x1c,0xa6,0xb4,0xc6,0xe8,0xdd,0x74,0x1f,0x4b,0xbd,0x8b,0x8a,
           0x70,0x3e,0xb5,0x66,0x48,0x03,0xf6,0x0e,0x61,0x35,0x57,0xb9,0x86,0xc1,0x1d,0x9e,
           0xe1,0xf8,0x98,0x11,0x69,0xd9,0x8e,0x94,0x9b,0x1e,0x87,0xe9,0xce,0x55,0x28,0xdf,
           0x8c,0xa1,0x89,0x0d,0xbf,0xe6,0x42,0x68,0x41,0x99,0x2d,0x0f,0xb0,0x54,0xbb,0x16]
end