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Historic Letterlocking Technique Used by European Royalty Mirrors Modern Encryption for Information Security


Before the days of password protection and multi-factor authentication, royal correspondence in Europe was safeguarded with a complex paper folding technique that “locked” letters to keep them sealed until they reached their recipients.

Used by Catherine de’ Medici, Queen Elizabeth, Mary, Queen of Scots, and other European royalty, spiral letterlocking consists of writing and folding a letter, slicing a dangling strip of its paper, and using that strip as a thread to sew stiches that turn the paper into its own envelope. The recipient would have to cut the “lock” to open the letter, making it impossible for a spy to open and read it undetected. This security technique is being studied by a group of scholars at M.I.T., who recently revealed their findings in the Electronic British Library Journal in order to help other researchers identify letterlocked papers that have been opened, flattened, and even repaired.

Letterlocking took hours of painstaking work in order to ensure that royal communications were private, and its use declined as mail systems improved. In modern times, encryption is used to secure electronic communications, offering a parallel assurance that sensitive information can be delivered confidentially. Many national and international standards contribute to evolving encryption technology that keeps data safe today.

INCITS/ISO/IEC 18033 is a standards series that covers different types of encryption algorithms used in online communications and transactions. Developed by Joint Technical Committee ISO/IEC JTC 1, Information Technology, Subcommittee (SC) 27, Information security, cybersecurity and privacy protection, these American National Standards (ANS) guide many elements of data security, such as different kinds of ciphers that encrypt and decrypt data for confidentiality. The U.S. plays a leading role in JTC 1, with the American National Standards Institute (ANSI) serving as Secretariat. The InterNational Committee for Information Technology Standards (INCITS), an ANSI member and accredited standards developer, administers the U.S. Technical Advisory Group (TAG) to ISO/IEC JTC 1.

Sensitive financial information like credit card data is frequently transmitted during retail transactions, and encryption standards help to reduce the vulnerability of that information. ANSI X9.119-1, Retail Financial Services – Requirements for Protection of Sensitive Payment Care Data – Part 1: Using Encryption Method, addresses security requirements and implementation for methods to protect credit and debit card data and reduce vulnerability to theft. This ANS was developed by Accredited Standards Committee X9, an ANSI member and accredited standards developer.

Beyond securing confidential information in communications and financial transactions, encryption also protects intellectual property in digital rights management systems. One ANS that supports the use of encryption is ANSI/SCTE 52, Data Encryption Standard – Cipher Block Chaining Packet Encryption Specification. This standard, developed by ANSI member and accredited standards developer the Society of Cable Telecommunications Engineers (SCTE), defines a method for encrypting MPEG-2 transport stream packets using the Data Encryption Standard (DES) Cipher Block Chaining (CBC) encryption standard.

Thanks to standards for data encryption, modern royalty and the general population alike can be assured that their communications are secure. Learn more about the history of royal letterlocking in The New York Times article: “How European Royals Once Shared Their Most Important Secrets