الفهرس 
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Abstract
The importance of E-mail is summarized in the exchange of messages and sensitive documents using computer technology and the Internet easily, instead of paper mail and fax. Due to the widespread use of e-mail between people, as well as among all local and universal organizations, many types of negative attacks have also spread. So, many individuals and organizations resort to protecting their e-mails. There are many secure systems used to protect e-mail messages as S/MIME (Secure/Multipurpose Internet Mail Extensions) and PGP (Pretty Good Privacy). However, they are in fact insufficient because of their many drawbacks. Therefore, this thesis aims to introduce a secure system, which achieve all the required security services (confidentiality, integrity, authentication, non-repudiation, public verification, and forward security) in an efficient way by using suggested methods and tools such as Elliptic curve (EC), and certificateless cryptography (CLC) together with the signcryption. EC provides better security than that provided by other schemes such as RSA (Rivest, Shamir, and Adelman). On the other hand, CLC overcomes many problems of Public Key Infrastructure (PKI) and Identity-based Public Key Cryptography (ID-PKC). In addition to, using the signcryption is more efficient through merging both the digital signature and the encryption into one logical step. Moreover, the proposed schemes can be applied on the real internet network system without making remarkable modifications to the currently existing email system. The security analysis of the proposed schemes has been provided. According to the obtained results, proposed schemes are more efficient than the existing email schemes as they have the least number of EC point multiplications without bilinear pairings operation which is time consuming. The thesis introduces also efficient multi-messages multi-receivers variant for the foregoing algorithm that has been proposed for the heterogeneous networks.