class HexaPDF::Encryption::RubyAES

Implementation of the general encryption algorithm AES.

Since this algorithm is implemented in pure Ruby, it is not very fast. Therefore the FastAES class based on OpenSSL should be used when possible.

For reference: This implementation is about 5000 times slower when decrypting and about 1800 times slower when encrypting than the FastAES version.

This implementation is using AES in Cipher Block Chaining (CBC) mode.

See: PDF1.7 s7.6.2

Public Class Methods

new(key, iv, mode) click to toggle source

Creates a new AES object using the given encryption key and initialization vector.

The mode must either be :encrypt or :decrypt.

# File lib/hexapdf/encryption/ruby_aes.rb, line 61
def initialize(key, iv, mode)
  @key = key
  @expanded_key_blocks = expand_key(@key)
  @prev_block = iv.bytes
  @mode = mode
end

Public Instance Methods

process(data) click to toggle source

Encrypts or decrypts the given data whose length must be a multiple of BLOCK_SIZE.

# File lib/hexapdf/encryption/ruby_aes.rb, line 69
def process(data)
  data = data.bytes

  (data.size / BLOCK_SIZE).times do |i|
    block = data[i * BLOCK_SIZE, BLOCK_SIZE]

    if @mode == :encrypt
      xor_blocks(block, @prev_block) # CBC: XOR plain text block with previous cipher block
      send(@mode, block)
      @prev_block = block
    else
      prev = block.dup
      send(@mode, block)
      xor_blocks(block, @prev_block) # CBC: XOR plain text block with previous cipher block
      @prev_block = prev
    end

    data[i * BLOCK_SIZE, BLOCK_SIZE] = block
  end

  data.pack('C*')
end