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