Class: PDF::Reader::Rc4SecurityHandler

Inherits:
Object
  • Object
show all
Defined in:
lib/pdf/reader/rc4_security_handler.rb

Overview

Decrypts data using the RC4 algorithim defined in the PDF spec. Requires a decryption key, which is usually generated by PDF::Reader::StandardKeyBuilder

Instance Method Summary collapse

Constructor Details

#initialize(key) ⇒ Rc4SecurityHandler

Returns a new instance of Rc4SecurityHandler.



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# File 'lib/pdf/reader/rc4_security_handler.rb', line 15

def initialize(key)
  @encrypt_key = key
end

Instance Method Details

#decrypt(buf, ref) ⇒ Object

7.6.2 General Encryption Algorithm

Algorithm 1: Encryption of data using the RC4 algorithm

version <=3 or (version == 4 and CFM == V2)

buf - a string to decrypt ref - a PDF::Reader::Reference for the object to decrypt



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# File 'lib/pdf/reader/rc4_security_handler.rb', line 28

def decrypt( buf, ref )
  objKey = @encrypt_key.dup
  (0..2).each { |e| objKey << (ref.id >> e*8 & 0xFF ) }
  (0..1).each { |e| objKey << (ref.gen >> e*8 & 0xFF ) }
  length = objKey.length < 16 ? objKey.length : 16
  rc4 = RC4.new( Digest::MD5.digest(objKey)[0,length] )
  rc4.decrypt(buf)
end