1) Whitfield Diffie and Martin Hellman and Ralph Merkle - (The earliest known origins of encryption systems were merely what people termed secret "codes". The first use of secret codes was probably by the sacred Jewish writers of ancient times. They used a secret code, called atbash, to write their manuscripts. It consisted of reversing the letters of their alphabet when writing.
Public key cryptography was invented in 1976 by Whitfield Diffie and Martin Hellman. For this reason, it is sometime called Diffie-Hellman encryption. It is also called asymmetric encryption because it uses two keys instead of one key (symmetric encryption).
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In the late 70s, a pair of Stanford scientists (Merkle and Hellman) invented a better electronic lock-and- key system -- called public key cryptography-- and a trio of MIT scientists (Rivest, Shamir and Adelman) invented what is today the de facto standard public key algorithm -- RSA public key cryptography. The idea behind public key cryptography is that the single DES key is replaced by a key pair comprising a public key and a private key.)
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Having the idea was one thing, finding a way to make it work was another. Diffie, Hellman and Merkle tried to come up with a viable method. In the end, they managed to find a method, known as Diffie-Hellman key agreement, for two people to agree on a shared, secret symmetric key using only public messages. It was nice, but it wasn't public-key encryption. The discovery of a true public-key encryption system was left to Ron Rivest, Adi Shamir and Leonard Adelman, who were working at MIT. Their system, named the RSA cryptosystem after them (with Rivest's name first because he was the person who finally made the breakthrough), was based on the difficulty of finding the divisors of large numbers (a process known as factoring).
2) 1976, NSA forced IBM to intentionally weaken the system down to 56 bits (DES utilizes a 64-bit key; however, 8 bits are for error detection thereby effectively making DES a 56-bit key system for security purposes. NSA ( National Security Agency ) whose primary function is to break security against US advised NBS in modifying the algorithm. The original proposal had key length of 112 bits. It was changed to 56. Some of the S-boxes were also modified.
NSA was suspected to have made changes to the algorithm to hold a trapdoor. There is another possible explanation - NSA made the changes to ensure that there were no trapdoors (inserted by IBM).
NSA may have expected that encryption will be implemented in hardware and that the algorithm will be secret. But the algorithm was made public in the standard. So they expected DES to be vulnerable to "Moore's Law".)
3) Key Escrow Systems - symmetric key encryption system 16-round Feistel cipher - (Feistel was one of the people who produced a more secure product cipher and implemented it in an encryption system called LUCIFER. Soon afterward a new algorithm was designed by IBM under the leadership of Dr W. L. Tuchman. This new algorithm used sixteen alternate steps of substitution and fixed permutations. All this was controlled by the key. This new algorithm was approved by the National Bureau of Standards on July 15th 1977. This new algorithm became known as the Data Encryption Standard.)
4) two parties (a=alice, b=bob) who communicate. Sender & receiver (
Pictures of Alice and Bob)