Question

I have to convert the following code into Qt c++
So I need to understand what these lines to.

@key in this code is a pem key file contents by openssl

key = [e-mail]_key.to_der

1. so i think this is converting that key to der format and then combining it with KEY.
   is it right?

2. whats does this do? to_sizet(key.size)
   As you can see the function returns [num].pack(‘V’). But i dont know wht does it do? I mean [num].pavck(‘V’). what is it?

3. And whats does this mean. key.size is it the strlen of key?

def write_crx
   print "write crx..." if @verbose
   key = [e-mail]_key.to_der
   File.open(@crx, 'wb') do |file|
     file << MAGIC
     file << EXT_VERSION
     file << to_sizet(key.size)
     file << to_sizet(@sig.size)
     file << key
     file << @sig
     File.open(@zip, 'rb') do |zip|
       file << zip.read
     end
   end
   puts "done at \"#{@crx}\"" if @verbose
 end
 def to_sizet num
   return [num].pack('V')
 end

Well I have one more Question. Forgot to add last time.
what does this line do?

KEY = %w(30 81 9F 30 0D 06 09 2A 86 48 86 F7 0D 01 01 01 05 00 03 81 8D 00).map{|s| s.hex}.pack('C*')

Answer 1

so i think this is converting that key to der format and then combining it with KEY. is it right?

Yes.

whats does this do? to_sizet(key.size) As you can see the function returns [num].pack(‘V’). But i dont know wht does it do? I mean [num].pavck(‘V’). what is it?

Well, just have a look at what the documentation on Array#pack says. With the V modifier, it just converts the array to a binary representation of a 32 bit unsigned integer type.

And whats does this mean. key.size is it the strlen of key?

Again, the Ruby documentation helps. String#size is indeed the string length.

what does this line do?

KEY = %w(30 81 9F 30 0D 06 09 2A 86 48 86 F7 0D 01 01 01 05 00 03 81 8D 00)
        .map{|s| s.hex}.pack('C*')

%(…) defines an array where each of its entries, separated by whitespace is treated as a separate string. %w(one two) is essentially a shorthand for ["one", "two"].

After that, we have to look up (again in the documentation) the meanings of Array#map and String#hex.

map simply applies an operation to each element of an array and creates a new array with the result. The operation is s.hex – that is, parse each of the strings as a hexadecimal number.

The result is once again packed, this time using the C* operation which, the documentation tells us, converts the numbers into their corresponding (unsigned) 8-bit character codes.

In summary: that line converts the hexadecimal values into a string of their respective characters.

Afterthought: you should really install Ruby and play a bit with the interactive Ruby console, irb. Keying in the above line already helps a lot:

$ irb
>> %w(30 81 9F 30 0D 06 09 2A 86 48 86 F7 0D 01 01 01 05 00 03 81 8D 00).map{|s| s.hex}
=> [48, 129, 159, 48, 13, 6, 9, 42, 134, 72, 134, 247, 13, 1, 1, 1, 5, 0, 3, 129, 141, 0]
>> %w(30 81 9F 30 0D 06 09 2A 86 48 86 F7 0D 01 01 01 05 00 03 81 8D 00).map{|s| s.hex}.pack('C*')
=> "0\201\2370\r\006\t*\206H\206\367\r\001\001\001\005\000\003\201\215\000"