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# coding: utf-8
# typed: strict
# frozen_string_literal: true
require 'digest'
require 'openssl'
class PDF::Reader
# 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
#
class AesV3SecurityHandler
#: (String) -> void
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
##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
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
#: (String, PDF::Reader::Reference, ?bool) -> String
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
end
end
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