class PDF::Reader::AesV2SecurityHandler


a decryption key, which is usually generated by PDF::Reader::StandardKeyBuilder
Decrypts data using the AESV2 algorithim defined in the PDF spec. Requires

def decrypt( buf, ref )


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

version == 4 and CFM == AESV2

Algorithm 1: Encryption of data using the AES-128-CBC algorithm

#7.6.2 General Encryption Algorithm 
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 ) }
  objKey << 'sAlT'  # Algorithm 1, b)
  length = objKey.length < 16 ? objKey.length : 16
  cipher = OpenSSL::Cipher.new("AES-#{length << 3}-CBC")
  cipher.decrypt
  cipher.key = Digest::MD5.digest(objKey)[0,length]
  cipher.iv = buf[0..15]
  cipher.update(buf[16..-1]) + cipher.final
end

def initialize(key) 

def initialize(key)
  @encrypt_key = key
end