1.3. POSTWAR CRYPTOGRAPHY, COMPUTERS, AND SECURITY 13 in the 1950s. Aldridge Ames had been divulging secrets for at least ten years and had been in contact with many Russians as a CIA recruiter. He applied cryptographic techniques to conceal his schemes, some as simple as B meaning meet in Bogota, Columbia, while others involved a series of chalk-marked mailboxes with codenames like “north” and “smile”, signaling brief commands like “travel on”. At the time of this writing, he is serving a life sentence in prison for treason. Cryptology continued to use codes and ciphers but was intensified, and it became more sophisticated with the improvements in computer technology. Horse Feistel of IBM in the 1970s developed a process of computer enhanced transposition of numbers using binary digits. It began as a demonstration cipher. Known as Demon, and then Lucifer, this DES cipher is a com- plicated encrypting procedure built upon groups of 64 plaintext bits, six of which were parity bits to guarantee accuracy. Simultaneously, Professor Martin Hellman and students Whitfield Diffie and Ralph Merkle collabo- rated to present the public key as a solution to the problem of distributing individual keys. This system had a primary basis of two keys. One was published and the other was kept private (see §8.5). For a while this system proved unbreakable, but in 1982 a trio of mathematicians from MIT broke it. They, Leonard Adleman, Ronald Rivest, and Adi Shamir, created an- other two-key procedure based on prime numbers. Their public key version is called RSA, and it is discussed in Chapter 8. RSA is slower to implement than DES because of its many computations, but is useful in networks where there are many communicants and the exchange of keys is a problem. Today, matters of security are ever present as Social Security numbers, bank account numbers, employment data, and others are digitized on a daily basis. Some of the alphanumeric components used include door open- ers, passwords, health plan numbers, PIN numbers, and many more. Even though these are not intended as encryptions, they are nonetheless to be kept hidden for privacy and security reasons. The U.S. government became ob- sessed with a system developed in the 1990’s called Pretty Good Privacy (PGP) for email, because they could not access emails when they thought they needed to. PGP has since been replaced by a system not nearly as good. A system called key escrow involved sending and receiving equip- ment that electronically chose algorithms from millions of available keys to encrypt conversations or data exchanges. The keys were to be held by two secure agencies of the federal government and required court-approved permission to access. It never gained public approval. As computer technology improves, new codes and ciphers are developed for encryption, and attempts are made at decryption, often successfully. In some cases, old techniques, such as steganography, are made even better. Steganography is the technique of passing a message in a way that even the existence of the message is unknown. The term is derived from the Greek steganos (which means covered) and graphein (to write). In the past, it was often used interchangeably with cryptography, but by 1967 it became
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