class PDF::Reader::AesV3SecurityHandler

Decrypts data using the AESV3 algorithim defined in the PDF 1.7, Extension Level 3 spec. Requires a decryption key, which is usually generated by PDF::Reader::KeyBuilderV5

Public Class Methods

new(key) click to toggle source

: (String) -> void

# File lib/pdf/reader/aes_v3_security_handler.rb, line 16
def initialize(key)
  if key.bytesize != 32
    raise PDF::Reader::MalformedPDFError.new(
      "AES-256 key must be exactly 32 bytes, got #{key.bytesize}"
    )
  end
  @encrypt_key = key
  @cipher = "AES-256-CBC" #: String
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 or AES algorithms

used to decrypt RC4/AES encrypted PDF streams (buf). Input data should be in bytesizes of
a multiple of 16, anything else is an error. The first 16 bytes are the initialization
vector, so any input of exactly 16 bytes decrypts to an empty string

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

: (String, PDF::Reader::Reference) -> String

# File lib/pdf/reader/aes_v3_security_handler.rb, line 38
def decrypt( buf, ref )
  if buf.bytesize % 16 > 0
    raise PDF::Reader::MalformedPDFError.new("Ciphertext not a multiple of 16")
  elsif buf.bytesize == 16
    return ""
  else
    begin
      internal_decrypt(buf, ref)
    rescue OpenSSL::Cipher::CipherError
      # If we failed to decrypt it might be a padding error, so try again
      # and assume no padding in the ciphertext. This will "suceed" but might
      # return garbage if the key is incorrect but that's OK - well before this
      # class is used we have confirmed the user provided key is correct so if
      # this works without error we can be confident the returned plaintext is
      #  correct
     internal_decrypt(buf, ref, false)
    end
  end
end

Private Instance Methods

internal_decrypt(buf, ref, padding = true) click to toggle source

: (String, PDF::Reader::Reference, ?bool) -> String

# File lib/pdf/reader/aes_v3_security_handler.rb, line 61
def internal_decrypt(buf, ref, padding = true)
  cipher = OpenSSL::Cipher.new(@cipher)
  cipher.decrypt
  cipher.padding = 0 unless padding
  cipher.key = @encrypt_key.dup
  cipher.iv = buf[0..15]
  cipher.update(buf[16..-1]) + cipher.final
end