Skip to content

Instantly share code, notes, and snippets.

@jagdeepsingh

jagdeepsingh/aes.rb

Created November 17, 2017 11:15
Show Gist options
  • Save jagdeepsingh/06e848326a8c49a431299c470630e7a6 to your computer and use it in GitHub Desktop.
Save jagdeepsingh/06e848326a8c49a431299c470630e7a6 to your computer and use it in GitHub Desktop.
Download ZIP
AES CTR algorithm in Ruby
Raw
aes.rb
module Paygate
class Aes
# Pre-computed multiplicative inverse in GF(2^8)
S_BOX = [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
# Round Constant used for the Key Expansion [1st col is 2^(r-1) in GF(2^8)]
R_CON = [[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
# Block size (in words): no of columns in state (fixed for AES)
CIPHER_BLOCK_SIZE = 4.freeze
# AES Cipher function: encrypt 'input' state with Rijndael algorithm
# applies Nr rounds (10/12/14) using key schedule w for 'add round key' stage
# @param int[] input 16-byte (128-bit) input state array
# @param int[][] w Key schedule as 2D byte-array (Nr+1 x Nb bytes)
# @returns int[] Encrypted output state array
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
# 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)
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 == 0
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
# apply SBox to state
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
# shift row r of state S left by r bytes
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 # note that this will work for nb = 4,5,6, but not 7,8 (always 4 for AES):
state # see asmaes.sourceforge.net/rijndael/rijndaelImplementation.pdf
end
# combine bytes of each col of state S
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 == 0) ? (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
# xor Round Key into state S
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
# apply SBox to 4-byte word w
def self.sub_word(word)
0.upto(3){ |i| word[i] = S_BOX[word[i]] }
word
end
# rotate 4-byte word w left by one byte
def self.rotate_word(word)
tmp = word[0]
0.upto(2){ |i| word[i] = word[i + 1] }
word[3] = tmp
word
end
end
end
Raw
aes_ctr.rb
require 'base64'
module Paygate
class AesCtr
# Encrypt a text using AES encryption in Counter mode of operation
#
# Unicode multi-byte character safe
#
# @param string plaintext Source text to be encrypted
# @param string password The password to use to generate a key
# @param int num_bits Number of bits to be used in the key (128, 192, or 256)
# @returns string Encrypted text
def self.encrypt(plaintext, password, num_bits)
block_size = 16 # block size fixed at 16 bytes / 128 bits (Nb=4) for AES
return '' unless num_bits.in?([128, 192, 256])
# use AES itself to encrypt password to get cipher key (using plain password as source for key
# expansion) - gives us well encrypted key (though hashed key might be preferred for prod'n use)
num_bytes = num_bits / 8 # no bytes in key (16/24/32)
pw_bytes = []
0.upto(num_bytes - 1){ |i| pw_bytes[i] = password.bytes.to_a[i] & 0xff || 0} # use 1st 16/24/32 chars of password for key #warn
key = Aes.cipher(pw_bytes, Aes.key_expansion(pw_bytes)) # gives us 16-byte key
key = key + key[0, num_bytes - 16] # expand key to 16/24/32 bytes long
# initialise 1st 8 bytes of counter block with nonce (NIST SP800-38A §B.2): [0-1] = millisec,
# [2-3] = random, [4-7] = seconds, together giving full sub-millisec uniqueness up to Feb 2106
counter_block = []
nonce = Time.now.to_i
nonce_ms = nonce % 1000
nonce_sec = (nonce / 1000.0).floor
nonce_rand = (rand() * 0xffff).floor
0.upto(1){ |i| counter_block[i] = urs(nonce_ms, i * 8) & 0xff }
0.upto(1){ |i| counter_block[i + 2] = urs(nonce_rand, i * 8) & 0xff }
0.upto(3){ |i| counter_block[i + 4] = urs(nonce_sec, i * 8) & 0xff }
# and convert it to a string to go on the front of the ciphertext
ctr_text = ''
0.upto(7){ |i| ctr_text += counter_block[i].chr }
# generate key schedule - an expansion of the key into distinct Key Rounds for each round
key_schedule = Aes.key_expansion(key)
block_count = (plaintext.length / block_size.to_f).ceil
cipher_text = []
0.upto(block_count - 1) do |b|
# set counter (block #) in last 8 bytes of counter block (leaving nonce in 1st 8 bytes)
# done in two stages for 32-bit ops: using two words allows us to go past 2^32 blocks (68GB)
0.upto(3){ |c| counter_block[15 - c] = urs(b, c * 8) & 0xff }
0.upto(3){ |c| counter_block[15 - c - 4] = urs(b / 0x100000000, c * 8) }
cipher_cntr = Aes.cipher(counter_block, key_schedule) # -- encrypt counter block --
# block size is reduced on final block
block_length = b < block_count - 1 ? block_size : (plaintext.length - 1) % block_size + 1
cipher_char = []
0.upto(block_length - 1) do |i|
cipher_char[i] = (cipher_cntr[i] ^ plaintext.bytes.to_a[b * block_size + i]).chr
end
cipher_text[b] = cipher_char.join
end
cipher_text = ctr_text + cipher_text.join
cipher_text = Base64.encode64(cipher_text).gsub(/\n/, '') + "\n"; # encode in base64
end
# Decrypt a text encrypted by AES in counter mode of operation
#
# @param string ciphertext Source text to be encrypted
# @param string password The password to use to generate a key
# @param int nBits Number of bits to be used in the key (128, 192, or 256)
# @returns string
# Decrypted text
def self.decrypt(ciphertext, password, nBits)
blockSize = 16 # block size fixed at 16 bytes / 128 bits (Nb=4) for AES
return '' unless(nBits==128 || nBits==192 || nBits==256)
ciphertext = Base64.decode64(ciphertext);
nBytes = nBits/8 # no bytes in key (16/24/32)
pwBytes = []
0.upto(nBytes-1){|i| pwBytes[i] = password.bytes.to_a[i] & 0xff || 0}
key = Aes.cipher(pwBytes, Aes.key_expansion(pwBytes)) # gives us 16-byte key
key = key.concat(key.slice(0, nBytes-16)) # expand key to 16/24/32 bytes long
# recover nonce from 1st 8 bytes of ciphertext
counterBlock = []
ctrTxt = ciphertext[0,8]
0.upto(7){|i| counterBlock[i] = ctrTxt.bytes.to_a[i]}
#generate key Schedule
keySchedule = Aes.key_expansion(key);
# separate ciphertext into blocks (skipping past initial 8 bytes)
nBlocks = ((ciphertext.length-8)/blockSize.to_f).ceil
ct=[]
0.upto(nBlocks-1){|b|ct[b] = ciphertext[8+b*blockSize, 16]}
ciphertext = ct; # ciphertext is now array of block-length strings
# plaintext will get generated block-by-block into array of block-length strings
plaintxt = [];
0.upto(nBlocks-1) do |b|
0.upto(3){|c| counterBlock[15-c] = urs(b,c*8) & 0xff}
0.upto(3){|c| counterBlock[15-c-4] = urs((b+1)/(0x100000000-1),c*8) & 0xff}
cipherCntr = Aes.cipher(counterBlock, keySchedule) # encrypt counter block
plaintxtByte = []
0.upto(ciphertext[b].length - 1) do |i|
# -- xor plaintxt with ciphered counter byte-by-byte --
plaintxtByte[i] = (cipherCntr[i] ^ ciphertext[b].bytes.to_a[i]).chr;
end
plaintxt[b] = plaintxtByte.join('')
end
plaintext = plaintxt.join('')
end
private
# Unsigned right shift function, since Ruby has neither >>> operator nor unsigned ints
#
# @param a number to be shifted (32-bit integer)
# @param b number of bits to shift a to the right (0..31)
# @return a right-shifted and zero-filled by b bits
def self.urs(a, b)
a &= 0xffffffff
b &= 0x1f
if a & 0x80000000 && b > 0 # if left-most bit set
a = ((a >> 1) & 0x7fffffff) # right-shift one bit & clear left-most bit
a = a >> (b - 1) # remaining right-shifts
else # otherwise
a = (a >> b); # use normal right-shift
end
a
end
end
end
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment