The American National Security Agency (NSA) adopted the 56-bit version of Horst Feistel’s Lucifer cipher (a German emigrant to the United States, an IBM employee), calling it DES (Data Encryption Standard). It would remain the standard for encrypted communications for several decades. The NSA’s concern at the time was to have a standard cipher for the civilian community that was secure but also decryptable with the NSA’s (military) resources. A 56-bit cipher has approximately 100 trillion keys, which satisfy this criterion. However, the problem of key distribution remained. The only secure way was to do it personally. Until the development of Public Key Cryptography, in the same years, in fact…
