Module: BytesManipulation

Included in:
Connection, Crypto
Defined in:
lib/bytes_manip.rb

Overview

Convenience methods to manipulate bytes.

Instance Method Summary collapse

Instance Method Details

#bs_rotate(bs, n = 1) ⇒ Object

Rotate a byte string by n bytes to the right. n can be negative, and efault to 1.



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# File 'lib/bytes_manip.rb', line 31

def bs_rotate(bs, n=1)
   bs.unpack('C*').rotate(n).pack('C*')
end

#bs_xor(bs1, bs2) ⇒ Object

Xors together two byte strings of the same length.



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# File 'lib/bytes_manip.rb', line 20

def bs_xor(bs1, bs2)
  fail unless bs1.bytesize == bs2.bytesize
  out = String.new(bs1)
  (0 .. bs1.bytesize - 1).each do |i|
    out.setbyte(i, bs1.getbyte(i) ^ bs2.getbyte(i))
  end
  out
end

#desfire_crc(data) ⇒ Object

DESFire-specific CRC algorithm taking a byte string as input and returning a byte string of length 2 as output.



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# File 'lib/bytes_manip.rb', line 37

def desfire_crc(data)
  wCRC = 0x6363
  data.each_byte do |byte|
    byte = (byte ^ (wCRC & 0x00FF)) % 256
    byte = (byte ^ (byte << 4)) % 256
    wCRC = ((wCRC >> 8) ^ (byte << 8) ^ (byte << 3) ^ (byte >> 4)) % 65536
  end
  [wCRC & 0xFF, (wCRC >> 8) & 0xFF].pack("C*")
end

#to_hex_array(array) ⇒ Object

Converts a byte array to an array holding strings representing the numbers in base 16. For debugging purposes.



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# File 'lib/bytes_manip.rb', line 15

def to_hex_array(array)
  array.flatten.map { |e| e.to_s(16) }
end

#to_le_array(num, n) ⇒ Object

Converts a number to a little-endian array of n bytes.



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# File 'lib/bytes_manip.rb', line 5

def to_le_array(num, n)
  out = Array.new(n)
  out.each_index do |i|
    out[i] = num % 256
    num /= 256
  end
end