Module: Kindle::DRM

Defined in:
lib/kindle/drm.rb

Constant Summary collapse

LETTERS = 
"ABCDEFGHIJKLMNPQRSTUVWXYZ123456789".split(//)

Instance Method Summary collapse

Instance Method Details

#checksumPid(s) ⇒ Object

Generates the actual Personal ID (PID) needed to tie/untie content (such as .mobi/.azw files) to a specific device.



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# File 'lib/kindle/drm.rb', line 16

def checksumPid(s)
	tmp = crc32(s)
	crc = tmp ^ (tmp >> 16)
	res = s
	l = LETTERS.length
	for i in 0..1 do
		b = crc & 0xFF
		t = b.divmod(l)[0]
		pos = t ^ (b % l)
		res = "#{res}#{LETTERS[pos % l]}"
		crc >>= 8
	end
	res
end

#crc32(s) ⇒ Object

Special cyclical redundancy check (checksumming) function.



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# File 'lib/kindle/drm.rb', line 10

def crc32(s)
	(~Zlib.crc32(s, -1)) & 0xFFFFFFFF
end

#serialToDeviceTypeAndPidSize(serial) ⇒ Object 



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# File 'lib/kindle/drm.rb', line 58

def serialToDeviceTypeAndPidSize(serial)
	type = nil
	size = nil
	pad = nil
	
	l = serial.length
	if l == 16
		case serial[0, 4]
		when /^B001/
			type = "Kindle 1"
		when /^B101/
			type = "Kindle 1"
		when /^B002/
			type = "Kindle 2"
		when /^B003/
			type = "Kindle 2 International"
		when /^B004/
			type = "Kindle DX"
		when /^B005/
			type = "Kindle DX 2"
		when /^B009/
			type = "Kindle DX International 2 (Graphite)"
		when /^B/
			type = "Unknown Kindle model. Please report!"
		end
		size = 7
		pad = '*'
	elsif l == 40
		type = "iPhone"
		size = 8
	end

	return nil if type.nil? || size.nil?
	return [type, size, pad]
end

#serialToIntermediaryPid(s, l) ⇒ Object

Figures out the intermediary Personal ID (PID) of a device based on its serial number and expected length of the output. Apparently this varies by the type of device.



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# File 'lib/kindle/drm.rb', line 34

def serialToIntermediaryPid(s, l)
	crc = crc32(s)  
	arr1 = Array.new(l, 0)
	for i in 0..(s.length - 1) do
		code = s[i]
		code = code.ord if code.class == String # Fix for Ruby 1.9+
		arr1[i%l] ^= code
	end

	# Grab each CRC byte and OR with a portion of the 
	crc_bytes = [crc >> 24 & 0xff, crc >> 16 & 0xff, crc >> 8 & 0xff, crc & 0xff]
	for i in 0..(l - 1) do
		arr1[i] ^= crc_bytes[i&3]
	end

	pid = ""
	for i in 0..(l-1) do
		b = arr1[i] & 0xff
		pid += LETTERS[(b >> 7) + ((b >> 5 & 3) ^ (b & 0x1f))]
	end
	pid
end

#serialToPid(serial) ⇒ Object 



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# File 'lib/kindle/drm.rb', line 95

def serialToPid(serial)
	pid = nil
	type, size, pad = serialToDeviceTypeAndPidSize(serial)
	if type.nil?
		# No dice.. :(
	else
		ipid = serialToIntermediaryPid(serial, size)
		ipid += pad unless pad.nil?
		pid = checksumPid(ipid)
	end
	pid
end