DevSecOps-Security-Privacy History

Vernam Cipher – 1917 A.D.

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Vernam Cipher

Gilbert Vernam (1890–1960), Joseph Mauborgne (1881–1971)

“Most encryption algorithms are computationally secure. This means that while it’s theoretically possible to crack the cipher by trying every possible encryption key, in practice this isn’t possible because trying all of the keys would require too much computational power.

More than a century ago, Gilbert Vernam and Joseph Mauborgne came up with a cryptographic system that is theoretically secure: even with an infinite amount of computer power, it is impossible to crack a message encrypted with the Vernam Cipher, no matter how fast computers ever become.

Vernam’s cipher, today called a one-time pad, is unbreakable because the encrypted message, decrypted with an incorrect key, can result in a plausible-looking message. Indeed, it can result in every possible message, since the key is the same length as the message. That is, for any given ciphertext, there is a key that makes it decrypt as a verse from the Bible, a few lines from Shakespeare, and the text on this page. Without a way to distinguish a correct from an incorrect decryption, the cipher is theoretically unbreakable.

Working at American Telephone and Telegraph Company (now AT&T®) in 1917, Vernam created a stream cipher that encrypted messages one character at a time by combining each character of the message with a character of a key. At first Vernam thought that key could be simply another message, but the following year, working with Joseph Mauborgne, a captain in the US Army Signal Corps, the two realized that the key must be random and nonrepeating. This improved security substantially: if the key were another message, it would be possible to distinguish a probable key from one that was improbable. But if the key was truly random, then any key was equally possible. Together, the two inventors created what we now call a one-time pad, one of only two known encryption systems that are provably unbreakable (the other being quantum cryptography).

As it turns out, a banker named Frank Miller had also invented the concept of the one-time pad in 1882, but his pen-and-paper system was not widely publicized or used.”

SEE ALSO Manchester SSEM (1948), RSA Encryption (1977), Advanced Encryption Standard (2001)

One-time pad device used with SIGTOT cipher system used aboard President Roosevelt’s Douglas C-54 airplane.

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