Class: CombinePDF::PDFDecrypt

Inherits:
Object
  • Object
show all
Defined in:
lib/combine_pdf/combine_pdf_decrypt.rb

Instance Method Summary collapse

Constructor Details

#initialize(objects = [], root_doctionary = {}) ⇒ PDFDecrypt

Returns a new instance of PDFDecrypt.



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# File 'lib/combine_pdf/combine_pdf_decrypt.rb', line 11

def initialize objects=[], root_doctionary = {}
  @objects = objects
  @encryption_dictionary = root_doctionary[:Encrypt]
  raise "Cannot decrypt an encrypted file without an encryption dictionary!" unless @encryption_dictionary
  @root_doctionary = root_doctionary
  @padding_key = [ 0x28, 0xBF, 0x4E, 0x5E, 0x4E, 0x75, 0x8A, 0x41,
          0x64, 0x00, 0x4E, 0x56, 0xFF, 0xFA, 0x01, 0x08,
          0x2E, 0x2E, 0x00, 0xB6, 0xD0, 0x68, 0x3E, 0x80,
          0x2F, 0x0C, 0xA9, 0xFE, 0x64, 0x53, 0x69, 0x7A ]
  @key_crypt_first_iv_store = nil
  @encryption_iv = nil
  PDFOperations.change_references_to_actual_values @objects, @encryption_dictionary
end

Instance Method Details

#_perform_decrypt_proc_(object, decrypt_proc, encrypted_id = nil, encrypted_generation = nil, encrypted_filter = nil) ⇒ Object 



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# File 'lib/combine_pdf/combine_pdf_decrypt.rb', line 113

def _perform_decrypt_proc_ (object, decrypt_proc, encrypted_id = nil, encrypted_generation = nil, encrypted_filter = nil)
  case
  when object.is_a?(Array)
    object.map! { |item| _perform_decrypt_proc_(item, decrypt_proc, encrypted_id, encrypted_generation, encrypted_filter) }
  when object.is_a?(Hash)
    encrypted_id ||= object[:indirect_reference_id]
    encrypted_generation ||=  object[:indirect_generation_number]
    encrypted_filter ||= object[:Filter]
    if object[:raw_stream_content]
      stream_length = object[:Length]
      if stream_length.is_a?(Hash) && stream_length[:is_reference_only]
        stream_length = PDFOperations.get_refernced_object( @objects, stream_length)[:indirect_without_dictionary]
      end
      actual_length = object[:raw_stream_content].length
      warn "Stream registeded length was #{object[:Length].to_s} and the actual length was #{actual_length}." if actual_length < stream_length
      length = [ stream_length, actual_length].min
      object[:raw_stream_content] = decrypt_proc.call( (object[:raw_stream_content][0...length]), encrypted_id, encrypted_generation, encrypted_filter)
    end
    object.each {|k, v| object[k] = _perform_decrypt_proc_(v, decrypt_proc, encrypted_id, encrypted_generation, encrypted_filter) if k != :raw_stream_content && (v.is_a?(Hash) || v.is_a?(Array) || v.is_a?(String))} # assumes no decrypting is ever performed on keys
  when object.is_a?(String)
    return decrypt_proc.call(object, encrypted_id, encrypted_generation, encrypted_filter)
  else
    return object
  end
  
end

#decrypt ⇒ Object 



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# File 'lib/combine_pdf/combine_pdf_decrypt.rb', line 67

def decrypt
  raise_encrypted_error @encryption_dictionary unless @encryption_dictionary[:Filter] == :Standard
  @key = set_general_key
  case @encryption_dictionary[:V]
  when 1,2
    warn "trying to decrypt with RC4."
    # raise_encrypted_error
    _perform_decrypt_proc_ @objects, self.method(:decrypt_RC4)
  else
    raise_encrypted_error
  end
  #rebuild stream lengths?
  @objects
end

#decrypt_AES(encrypted, encrypted_id, encrypted_generation, encrypted_filter) ⇒ Object 



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# File 'lib/combine_pdf/combine_pdf_decrypt.rb', line 95

def decrypt_AES(encrypted, encrypted_id, encrypted_generation, encrypted_filter)
  ## extract encryption_iv if it wasn't extracted yet
  unless @encryption_iv
    @encryption_iv = encrypted[0..15].to_i
    #raise "Tryed decrypting using AES and couldn't extract iv" if @encryption_iv == 0
    @encryption_iv = 0.chr * 16
    #encrypted = encrypted[16..-1]
  end
  ## start decryption using padding strings
  object_key = @key.dup
  (0..2).each { |e| object_key << (encrypted_id >> e*8 & 0xFF ) }
  (0..1).each { |e| object_key << (encrypted_generation >> e*8 & 0xFF ) }
  object_key << "sAlT"
  key_length = object_key.length < 16 ? object_key.length : 16
  cipher = OpenSSL::Cipher::Cipher.new("aes-#{object_key.length << 3}-cbc").decrypt
  cipher.padding = 0
  (cipher.update(encrypted) + cipher.final).unpack("C*")
end

#decrypt_none(encrypted, encrypted_id, encrypted_generation, encrypted_filter) ⇒ Object 



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# File 'lib/combine_pdf/combine_pdf_decrypt.rb', line 81

def decrypt_none(encrypted, encrypted_id, encrypted_generation, encrypted_filter)
  "encrypted"
end

#decrypt_RC4(encrypted, encrypted_id, encrypted_generation, encrypted_filter) ⇒ Object 



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# File 'lib/combine_pdf/combine_pdf_decrypt.rb', line 84

def decrypt_RC4(encrypted, encrypted_id, encrypted_generation, encrypted_filter)
  ## start decryption using padding strings
  object_key = @key.dup
  object_key << [encrypted_id].pack('i')[0..2]
  object_key << [encrypted_generation].pack('i')[0..1]
  # (0..2).each { |e| object_key << (encrypted_id >> e*8 & 0xFF ) }
  # (0..1).each { |e| object_key << (encrypted_generation >> e*8 & 0xFF ) }
  key_length = object_key.length < 16 ? object_key.length : 16
  rc4 = RC4.new( Digest::MD5.digest(object_key)[(0...key_length)] )
  rc4.decrypt(encrypted)
end

#raise_encrypted_error(object = nil) ⇒ Object 



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# File 'lib/combine_pdf/combine_pdf_decrypt.rb', line 140

def raise_encrypted_error object = nil
  object ||= @encryption_dictionary.to_s.split(',').join("\n")
  warn "Data raising exception:\n #{object.to_s.split(',').join("\n")}"
  raise "File is encrypted - not supported."     
end

#set_general_key(password = "") ⇒ Object 



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# File 'lib/combine_pdf/combine_pdf_decrypt.rb', line 24

def set_general_key(password = "")
  # 1) make sure the initial key is 32 byte long (if no password, uses padding).
  key = (password.bytes[0..32] + @padding_key)[0..31].pack('C*').force_encoding(Encoding::ASCII_8BIT)
  # 2) add the value of the encryption dictionary’s O entry
  key << @encryption_dictionary[:O].to_s
  # 3) Convert the integer value of the P entry to a 32-bit unsigned binary number
  # and pass these bytes low-order byte first
  key << [@encryption_dictionary[:P]].pack('i')
  # 4) Pass the first element of the file’s file identifier array
  # (the value of the ID entry in the document’s trailer dictionary
  key << @root_doctionary[:ID][0]
  # # 4(a) (Security handlers of revision 4 or greater)
  # # if document metadata is not being encrypted, add 4 bytes with the value 0xFFFFFFFF.
  if @encryption_dictionary[:R] >= 4
    unless @encryption_dictionary[:EncryptMetadata] == false #default is true and nil != false
      key << "\x00\x00\x00\x00"
    else
      key << "\xFF\xFF\xFF\xFF"
    end
  end
  # 5) pass everything as a MD5 hash
  key = Digest::MD5.digest(key)
  # 5(a) h) (Security handlers of revision 3 or greater) Do the following 50 times:
  # Take the output from the previous MD5 hash and
  # pass the first n bytes of the output as input into a new MD5 hash,
  # where n is the number of bytes of the encryption key as defined by the value of
  # the encryption dictionary’s Length entry.
  if @encryption_dictionary[:R] >= 3
    50.times do|i|
      key = Digest::MD5.digest(key[0...@encryption_dictionary[:Length]])
    end
  end
  # 6) Set the encryption key to the first n bytes of the output from the final MD5 hash,
  # where n shall always be 5 for security handlers of revision 2 but,
  # for security handlers of revision 3 or greater,
  # shall depend on the value of the encryption dictionary’s Length entry.
  if @encryption_dictionary[:R] >= 3
    @key = key[0..(@encryption_dictionary[:Length]/8)]
  else
    @key = key[0..4]
  end
  @key
end