Class: Paygate::Aes

Inherits:
Object
  • Object
show all
Defined in:
lib/paygate/aes.rb

Constant Summary collapse

S_BOX =

Pre-computed multiplicative inverse in GF(2^8)

[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].freeze
R_CON =

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

[[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]].freeze
CIPHER_BLOCK_SIZE =

Block size (in words): no of columns in state (fixed for AES)

4

Class Method Summary collapse

Class Method Details

.add_round_key(state, w, rnd) ⇒ Object

xor Round Key into state S



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# File 'lib/paygate/aes.rb', line 131

def self.add_round_key(state, w, rnd)
  0.upto(3) do |r|
    0.upto(CIPHER_BLOCK_SIZE - 1) { |c| state[r][c] ^= w[(rnd * 4) + c][r] }
  end
  state
end

.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/paygate/aes.rb', line 44

def self.cipher(input, w)
  nr = (w.length / CIPHER_BLOCK_SIZE) - 1 # no of rounds: 10/12/14 for 128/192/256-bit keys
  state = [[], [], [], []] # initialize 4x4 byte-array 'state' with input

  (0...(4 * CIPHER_BLOCK_SIZE)).each do |i|
    state[i % 4][(i / 4.0).floor] = input[i]
  end

  state = add_round_key(state, w, 0)
  (1...nr).each do |round|
    state = sub_bytes(state)
    state = shift_rows(state)
    state = mix_columns(state)
    state = add_round_key(state, w, round)
  end

  state = sub_bytes(state)
  state = shift_rows(state)
  state = add_round_key(state, w, nr)

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

.key_expansion(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/paygate/aes.rb', line 73

def self.key_expansion(key)
  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...(CIPHER_BLOCK_SIZE * (nr + 1))).each do |i|
    w[i] = []
    0.upto(3) { |t| temp[t] = w[i - 1][t] }
    if (i % nk).zero?
      temp = sub_word(rotate_word(temp))
      0.upto(3) { |t| temp[t] ^= R_CON[i / nk][t] }
    elsif nk > 6 && i % nk == 4
      temp = sub_word(temp)
    end
    0.upto(3) { |t| w[i][t] = w[i - nk][t] ^ temp[t] }
  end
  w
end

.mix_columns(state) ⇒ Object

combine bytes of each col of state S



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# File 'lib/paygate/aes.rb', line 113

def self.mix_columns(state)
  0.upto(3) do |c|
    a = []                  # 'a' is a copy of the current column from 'state'
    b = []                  # 'b' is a•{02} in GF(2^8)
    0.upto(3) do |i|
      a[i] = state[i][c]
      b[i] = (state[i][c] & 0x80).zero? ? (state[i][c] << 1) ^ 0x011b : state[i][c] << 1
    end
    # a[n] ^ b[n] is a•{03} in GF(2^8)
    state[0][c] = b[0] ^ a[1] ^ b[1] ^ a[2] ^ a[3]        # 2*a0 + 3*a1 + a2 + a3
    state[1][c] = a[0] ^ b[1] ^ a[2] ^ b[2] ^ a[3]        # a0 * 2*a1 + 3*a2 + a3
    state[2][c] = a[0] ^ a[1] ^ b[2] ^ a[3] ^ b[3]        # a0 + a1 + 2*a2 + 3*a3
    state[3][c] = a[0] ^ b[0] ^ a[1] ^ a[2] ^ b[3]        # 3*a0 + a1 + a2 + 2*a3
  end
  state
end

.rotate_word(word) ⇒ Object

rotate 4-byte word w left by one byte



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# File 'lib/paygate/aes.rb', line 145

def self.rotate_word(word)
  tmp = word[0]
  0.upto(2) { |i| word[i] = word[i + 1] }
  word[3] = tmp
  word
end

.shift_rows(state) ⇒ Object

shift row r of state S left by r bytes



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# File 'lib/paygate/aes.rb', line 103

def self.shift_rows(state)
  t = []
  1.upto(3) do |r|
    0.upto(3) { |c| t[c] = state[r][(c + r) % CIPHER_BLOCK_SIZE] }     # shift into temp copy
    0.upto(3) { |c| state[r][c] = t[c] }                               # and copy back
  end
  state # see asmaes.sourceforge.net/rijndael/rijndaelImplementation.pdf
end

.sub_bytes(state) ⇒ Object

apply SBox to state



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# File 'lib/paygate/aes.rb', line 95

def self.sub_bytes(state)
  0.upto(3) do |r|
    0.upto(CIPHER_BLOCK_SIZE - 1) { |c| state[r][c] = S_BOX[state[r][c]] }
  end
  state
end

.sub_word(word) ⇒ Object

apply SBox to 4-byte word w



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# File 'lib/paygate/aes.rb', line 139

def self.sub_word(word)
  0.upto(3) { |i| word[i] = S_BOX[word[i]] }
  word
end