byte manipulation in ruby

Byte Manipulation inRuby

Hi, I’m Harisankar P S

mailme@hsps.in | twitter.com/@coderhs

Cochin, IndiaEntrepreneur, Programmer

I am also the founder of

Ruby on Rails based software development Agency

http://redpanthers.co

“Hello World”.bytes

[72, 101, 108, 108, 111, 32, 87, 111, 114, 108, 100, 46]

LETS START WITH BASIC STUFF

97 #=> 97 in decimal (base 10)0x61 #=> 97 in hex (base 16)0141 #=> 97 in octal (base 8)0b01100001 #=> 97 in binary (base 2)

# These are all just different ways of typing the same thing:[0141, 0x61, 0b01100001, 97] #=> [97, 97, 97, 97]

Literals

97.to_s(10) #=> '97' (base 10)97.to_s(16) #=> '61' (base 16)97.to_s(8) #=> '141' (base 8)97.to_s(2) #=> '1100001' (base 2)

String/Bytes

97.chr #=> 'a''a'.ord #=> 97

Array#pack and String#unpack

Array#pack is a method for 'packing' an array into a string of bytes according to a certain format. Some examples:

hw_bytes = "Hello, world".bytes# => [72, 101, 108, 108, 111, 44, 32, 119, 111, 114, 108, 100]

# c* => Pack every element as an 8 bit signed integerhw_bytes.pack('c*') # => "Hello, world"

# s5 => Pack the first five elements as 16 bit signed integers

hw_bytes.pack('s5') # => "H\0e\0l\0l\0o\0"

# There's also an 'm' format that we can use for fast base64 encoding:["Hello, world"].pack('m0') #=> "SGVsbG8sIHdvcmxk"

http://ruby-doc.org/core-2.2.2/Array.html#method-i-pack

String#unpack takes you in the other direction: it lets you take a string in a certain binary format and 'unpack' it into an array:

# This says: read the string as a sequence 8-bit integers and "Hello, world".unpack('c*')# => [72, 101, 108, 108, 111, 44, 32, 119, 111, 114, 108, 100]

# Read as a sequence of 16 bit integers and put each"H\0e\0l\0l\0o\0,\0 \0w\0o\0r\0l\0d\0".unpack('s*')# => [72, 101, 108, 108, 111, 44, 32, 119, 111, 114, 108, 100]

# As with Array#pack, we can use the 'm' format and base64 decode"SGVsbG8sIHdvcmxk".unpack('m0') # => ["Hello, world"]

http://ruby-doc.org/core-2.2.2/String.html#method-i-unpack

XORing bits

XOR is a reversible way to 'mix' data together, and is the bread and butter operation of modern cryptography. At the logic level it means one or the other but not both and so for bits the truth table looks like this:

1 01 0 10 1 0

Like a lot of languages, in ruby the ^ operator denotes XOR. An example XOR with base 2 literals:

XOR two string

class String def xor_with(other_string) self.bytes.zip(other_string.bytes).map { |(a,b)| a ^ b }.pack('c*') endend

Chained Program to conver Base 32 string Base 64

Just for horror ;)

TABLE = “ABCDEFGHIJKLMNOPQRSTUVWXYZ234567"# Red Panthersbase_32 = ‘KJSWIICQMFXHI2DFOJZQ===='

puts [base_32.gsub('=','').chars.map { |s| TABLE.index(s) }.map { |s| s.to_s(2) }.map { |s| "0"*(5-s.length)+s}.join.chars.each_slice(8).map(&:join).map { |i| i.to_i(2) }.map { |s| s.chr }.join.strip].pack('m')

— Harisankar P S

“Thank you for listening :) ”

CREDITS

http://www.happybearsoftware.com/byte-manipulation-in-ruby.html

http://blog.bigbinary.com/2011/07/20/ruby-pack-unpack.html

http://ruby-doc.org