gistfile1.rb

require 'bindata'

module BlockSizeCalculator
  def ciphertext_block_size(block_size)
    block_size / CipherBlockSize +
      (0 == block_size % CipherBlockSize ? 0 : 1) * CipherBlockSize +
      CipherBlockSize
  end
end

class ChrisPalmer < BinData::Record
  include BlockSizeCalculator
  uint32 :block_size
  string :data, :read_length => lambda { ciphertext_block_size(block_size) }
end