class FFXCodec

Encode / decode two integers into a single integer with optional encryption

The resulting value is a single 32 or 64-bit unsigned integer (your choice), even when encrypted.

Works by divvying up the bits of the single integer between the two component integers and running it through AES-FFX format-preserving cipher (optional).

Constants

VERSION

Public Class Methods

new(a_size, b_size) click to toggle source

@param [Fixnum] a_size the number of bits allocated to the left integer @param [Fixnum] b_size the number of bits allocated to the right integer

# File lib/ffxcodec.rb, line 16
def initialize(a_size, b_size)
  @encoder = Encoder.new(a_size, b_size)
end

Public Instance Methods

bit_length() click to toggle source

Show size of the resulting integer in bits

@return [Fixnum] size of the combined integer in bits

# File lib/ffxcodec.rb, line 104
def bit_length
  @encoder.size
end

decode(c) click to toggle source

Decode an integer into its two component integers

@note input will automatically be decrypted if encryption was setup @param [Fixnum, Bignum] c value to decode

@example Decode unencrypted integer into component 40 and 24-bit integers

ffx = FFXCodec.new(40, 24)
ffx.decode(165828720871684)        #=> [1234567890, 4]

@example Decode encrypted integer into component 40 and 24-bit integers

ffx = FFXCodec.new(40, 24)
ffx.setup_encryption("2b7e151628aed2a6abf7158809cf4f3c", "9876543210")
ffx.decode(7692035069140451684)    #=> [797980150281, 5427652]

@return [Array<Fixnum>] component integers

# File lib/ffxcodec.rb, line 74
def decode(c)
  input = @crypto ? decrypt(c) : c
  @encoder.decode(input)
end

disable_encryption() click to toggle source

Turn off encryption

@return [void]

# File lib/ffxcodec.rb, line 34
def disable_encryption
  @crypto = false
end

encode(a, b) click to toggle source

Encode two integers into a single integer

@param [Fixnum] a value to encode @param [Fixnum] b value to encode

@example Encode 40 and 24-bit integers into an unencrypted 64-bit integer

ffx = FFXCodec.new(40, 24)
ffx.encode(1234567890, 4)          #=> 165828720871684

@example Encode 40 and 24-bit integers into an encrypted 64-bit integer

ffx = FFXCodec.new(40, 24)
ffx.setup_encryption("2b7e151628aed2a6abf7158809cf4f3c", "9876543210")
ffx.encode(797980150281, 5427652)  #=> 7692035069140451684

@return [Fixnum, Bignum] encoded integer if encryption not setup @return [Fixnum, Bignum] encrypted encoded integer if encryption setup

# File lib/ffxcodec.rb, line 54
def encode(a, b)
  c = @encoder.encode(a, b)
  @crypto ? encrypt(c) : c
end

maximums() click to toggle source

Show maximum representable base 10 value for each field

@example Maximums for a 32-bit integer split into 24 and 8-bit components

ffx = FFXCodec.new(24, 8)
ffx.maximums  #=> [16777215, 255]

@example Maximums for a 64-bit integer split into two 32-bit components

ffx = FFXCodec.new(32, 32)
ffx.maximums  #=> [4294967295, 4294967295]

@return [Array<Fixnum>] maximum representable component integers

# File lib/ffxcodec.rb, line 90
def maximums
  [@encoder.a_max, @encoder.b_max]
end

setup_encryption(key, tweak) click to toggle source

Setup encryption

Auto-enables encryption after encoding and decryption before decoding.

@param [String] key for AES as a hexadecimal string @param [String] tweak for AES @return [void]

# File lib/ffxcodec.rb, line 27
def setup_encryption(key, tweak)
  @crypto = Encrypt.new(key, tweak, @encoder.size, 2)
end

size() click to toggle source

Show size of the resulting integer in bytes

@return [Fixnum] size of the combined integer in bytes

# File lib/ffxcodec.rb, line 97
def size
  @encoder.size / 8
end

Private Instance Methods

decrypt(value) click to toggle source

@param [Fixnum, Bignum] value to decrypt

# File lib/ffxcodec.rb, line 116
def decrypt(value)
  @crypto.decrypt(value.to_s(2)).to_i(2)
end

encrypt(value) click to toggle source

@param [Fixnum, Bignum] value to encrypt

# File lib/ffxcodec.rb, line 111
def encrypt(value)
  @crypto.encrypt(value.to_s(2)).to_i(2)
end