He said, she said: The concept of non-repudiation

To repudiate is to deny; non-repudiation means that an action (such as an online transaction, e-mail communication, and so on) or occurrence can’t be easily denied. Non-repudiation is a related function of identification and authentication (I&A) and accountability. For example, it’s difficult for a user to deny sending an e-mail message that was digitally signed with that user’s private key. Likewise, it’s difficult to deny responsibility for an enterprise-wide outage if the accounting logs positively identify you (from username and strong authentication) as the poor soul who inadvertently issued the write-erase command on the core routers two seconds before everything dropped!

Tales from the crypt-o: A brief history of cryptography

Cryptography dates back over 4,000 years to the ancient Egyptians when hieroglyphs were used not to protect messages but to add mystique.

Around 400 B.C., the Spartans began using a military cryptography system known as the scytale, which consisted of a strip of parchment wrapped around a wooden rod of a specified secret length and diameter. The message to be encoded was written on the strip of parchment vertically down the rod and then unwrapped and sent by messenger to the intended recipient. The recipient had an identical rod to wrap the strip of parchment around and decode the message.

Around 50 B.C., Julius Caesar used a substitution cipher to transmit secret messages. This system involved substituting letters of the message with other letters from the same alphabet. For example, a simple encryption scheme may have required the sender to shift each letter three spaces to the right: so, A = D, B = E, C = F, and so on. The recipient would then shift the letters three spaces to the left to decrypt and read the message.

This system, which uses only a single alphabet to encrypt and decrypt an entire message, is known as a monoalphabetic substitution. This system was particularly effective for Caesar because most of the population was illiterate at the time.

In the 15th century, a cryptographic system utilizing concentric disks to provide substitution was used in Italy. In 1790, Thomas Jefferson invented an encryption device by using a stack of 26 individually rotating disks. The Japanese Purple Machine and German Enigma Machine are two examples of cryptographic devices used successfully during World War II — at least, until the Allies cracked the codes. More recently, Quaker Oats developed the Cap’n Crunch Magic Decoder Ring for encrypting and decrypting simple messages!