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Abstract
In most civil and military communications most messages are to be sent by electronic means rather than physically carried or mailed. These electronic means include those send by wires and those transmitted by radio . They can be sent by telephone, telegraph, teletypewriter, facsimile or computer over the internet. Electronic means provide greater speed than physical means , but make communications more vulnerable to be intercepted by opponents. Thus preventing the unauthorized interception of sensitive information is a legitimate need of not only military institutions and government, but also for private persons in the business and commercial sectors. Thus the term ” secure communications ” arises and hence cryptology becomes an important factor in the design of secure communication systems. The privacy of data , authentication , digital signature and identification are among the various elements needed to be considered to protect data over closed and open communication networks.
Cryptology is the knowledge which concerns secret communications in all its aspects. Two major areas of cryptology are cryptography and cryptanalysis . Cryptography is the branch of cryptology, concerned with protecting communication from being read by unauthorized people. Ciphers that are used to protect communications are called cryptographic systems . The application of ciphers to messages to make them unreadable is called encryption. The resulting messages are called cryptograms or ciphertexts. The persons who create and use cryptographic systems are called cryptographers. Cryptanalysis is the branch of cryptology concerned with solving the cryptographic systems used by others. The main object of a cryptanalyst is to recover the plaintext from the ciphertext and to recover the cryptographic system used . The plaintext is recovered for its potential intelligent value , and the system is recovered for application to future messages in the same or similar systems.
The public key cryptosystems were needed to satisfy the commercial need that overcame some of the disadvantages of the conventional or symmetric key cryptography. These started by a celebrated paper by Diffie and Hellman in 1976[9]. Security of data has evolved rapidly after the USA National Bureau of Standards used the Digital Encryption Standard (DES) as a federal standard in 1977. Over the next years the problem of protecting data and securing communications received increased attentions allover the world.
The 1980’s were full of public key cryptography such that many systems were proposed and most of them were broken. Of course a parallel progress was made in symmetric key cryptography. Also in those years the branch of cryptanaIysis evolved to be one of the most ave areas of research associated with a developed huge amount of useful mathematical tools used for analysis that paraIleled the increased computational ability of modem computers.
Secure and authenticated message delivery andlor storage represent one of the main aims of computer communication security research. The standard method to achieve this till 1997 wu digital signature followed by encryption where the message is first signed using a .mabIe digital signature scheme , then encrypted together with the signature.