Реферат: The Necessity Of Computer Security Essay Research

key, a sequence of eight numbers, each between 0 and 127. The other is a 2-key

system; in this approach to cryptography, a pair of mathematically complementary

keys, each containing as many as 200 digits, are used for encryptions and

decryption. In contrast with ciphers of earlier generations, where security

depended in part on concealing the algorithm, confidentiality of a computer

encrypted message hinges solely on the secrecy of the keys. Each system is

thought to encrypt a message so inscrutably that the step-by-step mathematical

algorithms can be made public without compromising security.

The single key system, named the Data Encryption Standard – DES for short -

was designed in 1977 as the official method for protecting unclassified computer

data in agencies of the American Federal government. Its evolution began in

1973 when the US National Bureau of Standards, responding to public concern

about the confidentiality of computerized information outside military and

diplomatic channels, invited the submission of data-encryption techniques as the

first step towards an encryption scheme intended for public use.

The method selected by the bureau as the DES was developed by IBM

researchers. During encryption, the DES algorithm divides a message into blocks

of eight characters, then enciphers them one after another. Under control of

the key, the letters and numbers of each block are scrambled no fewer than 16

times, resulting in eight characters of ciphertext.

As good as the DES is, obsolescence will almost certainly overtake it. The

life span of encryption systems tends to be short; the older and more widely

used a cipher is, the higher the potential payoff if it is cracked, and the

greater the likelihood that someone has succeeded.

An entirely different approach to encryption, called the 2-key or public-

key system, simplifies the problem of key distribution and management. The

approach to cryptography eliminates the need for subscribers to share keys that

must be kept confidential. In a public-key system, each subscriber has a pair

of keys. One of them is the so-called public key, which is freely available to