Hacking historyOrigami in reverseCracking the security on a trove of 17th-century lettersA modern correspondent wanting to communicate privately can use computerised encryption. Three hundred years ago, origami would have been a better bet.Before gummed envelopes became common in the 1800s, letters were posted with no security wrapper.Privacy-minded writers relied instead on cunning combinations of folds, tucks, slits and seals, a practice Jana Dambrogio at the Massachusetts Institute of Technology has dubbed "letterlocking".Some, like the "chapel fold", in which the letteris turned into its own envelope and sealed, were the equivalent of simple padlocks. Others were subtler.The "dagger trap"relied on a concealed wax seal that would leave a telltale rip once a letter had been opened.But information about the practice is scarce. Most historical letters survive in their opened form, leaving aficionados like Ms Dambrogio with little to go on but crease-marks and tears.The few that remain unopened present a different problem: how to read them without permanently damaging the letterlock.
