class PDF::Reader::Rc4SecurityHandler

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

Public Class Methods

new(key) click to toggle source
# File lib/pdf/reader/rc4_security_handler.rb, line 15
def initialize(key)
  @encrypt_key = key
end

Public Instance Methods

decrypt( buf, ref ) click to toggle source

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

# 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