DES & AES

DES stands for Data Encryption Standard, while AES stands for Advanced Encryption Standard. These two standards are all developed after the internet came to the world. After the internet was introduced to the world, computer security was more and more important because people can connect to the internet at any point of the world. Without standard to protect these information, anybody can access to the information in plain text.

So in 1972, NBS (National Bureau of Standards) started a study about computer security, but there was no satisfied response afterward. Then in 1974, IBM submitted a candidate answer. However, in a declassified NSA book named American Cryptology during the Cold War, 1945-1989 by Thomas R. Johnson, Johnson said that NBS solicited private industry for a data encryption standard (DES). The first offerings were disappointing, so NSA began working on its own algorithm. Then a deputy director for research and engineering, Howard Rosenblum discovered that Walter Tuchman of IBM was working on a modification to Lucifer for general use. NSA gave Tuchman a clearance and brought him in to work jointly with the Agency on his Lucifer modification. Also, the book indicated that NSA worked closely with IBM to strengthen the algorithm.

For DES, it is archetypal block cipher, an algorithm that takes a fixed-length string of plaintext bits and transfer the text into another cipher text bit string of the same length. The length used by DES is 64 bits. To make 64 bits text be encrypted, people need a key to start the process. Only the people who have the key to a specific text, they can read the text. The length of DES key is 64 bits. However, 8 bits of them are used to correction. So only 56 bits are actually used.

Since key of DES is 56 bits long, it is not too hard for the computer today to brute force attack the key. So we have the advanced version of DES, AES. AES was developed based on the Rijndael cipher by two Belgian cryptographers, Joan Daemen and Vincent Rijmen. The standard length for AES is 128 bits. However, people can use 256 bits version for security reason. However, computer professionals found some indirect ways to break AES. For example, there was a method to break AES by getting the cache of using the specific key for the AES. But the method need administrator authority to run. The AES is security for usage right now. However, there will be always a day that we have to abandon AES due to the development of technology.