الفهرس 
Scope of this thesisOnly 14 pages are availabe for public view
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Abstract
The growing number of instances of breaches in information security in the last few years has created a compelling case for efforts towards computer secure systems. Security has been the subject of intensive research in the areas of cryptography, computing, and networking. The demands for effective and secure communications is growing in consumer electronics, financial and other electronic transactions, so the security applications can provide an important way for consumers and businesses to decide which electronic communication they can trust. Collision-resistant hash functions are an important tool for cryptographic applications; they are used to fingerprint or digest messages before applying digital signature schemes, and find also applications in message authentication and the protection of passphrases. Encryption and signature schemes are fundamental cryptographic tools for providing privacy and authenticity, respectively. However, in several cryptographic applications, such as secure E-mail or secure channel establishment protocols, these two aspects are simultaneously required. The original signcryption concept was introduced by Zheng in 1997. This kind of scheme combines the functionality of a digital signature scheme with that of an encryption scheme. This thesis provides a new Secure and Fast Hashing Algorithm (SFHA- 256) which is based on a modified version of the Merkle-Damgard (MD) iterated construction and is more resistant against the recent multi-blocks attacks and the extension attacks. To increase the efficiency of the proposed algorithm, a step function with a reduced number of operations has been introduced.