class PDF::Reader::AesV2SecurityHandler

Decrypts data using the AESV2 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/aes_v2_security_handler.rb, line 14
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 AES-128-CBC algorithm

version == 4 and CFM == AESV2

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

# File lib/pdf/reader/aes_v2_security_handler.rb, line 27
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