10 th International Research/Expert Conference ”Trends in the Development of Machinery and Associated Technology” TMT 2006, Barcelona-Lloret de Mar, Spain, 11-15 September, 2006 DIGITAL SIGNATURE ALGORITHM (DSA) Assist. Hermina Alajbegović, B. Bc. Ph.D. Hasan Jamak Faculty of Mechanical Engineering University of Sarajevo Zenica B&H Faculty of natural sciences hermina@mf.unze.ba and mathematics, Ph.D. Dževad Zečić Faculty of Mechanical Engineering Zenica B&H ABSTRACT This paper presents one of the cryptography solutions about establishing user's identity and authentic documents on the Internet which are exchanged among users. These problems are very prevalent because the Internet plays an important and dominant role in the business world. In this paper, the existing solutions will be brought closer the readers who are not very familiar with cryptography and algebra. Codes of these solutions are created in Mathematica 4.0. Key words: computer security, digital signature, public-key cryptography, Federal Information Processing Standard. 1. INTRODUCTION In today’s developing and competitive business world, a great number of banks and other institutions use the Internet for servicing their customers. The exchange of documents requires special security measures to safeguard the information from unauthorized access. A digital signature is an electronic signature that can be used to authenticate the identity of the sender of a message or the signer of a document, and possibly to ensure that the original content of the message or document that has been sent is unchanged. Digital signatures are easily transportable, cannot be imitated by someone else, and can be automatically time-stamped (date and time are added to message and then that message is signed). The ability to ensure that the original signed message arrived means that the sender cannot easily repudiate it later. A digital signature can be used with any kind of message, whether it is encrypted or not, simply so that the receiver can be sure of the sender's identity and that the message arrived intact. Our primary goal is to simplify the application of the existing algorithms for this problem and in the continuation we provide those solutions. 2. DSA There is a vast number of digital signature algorithms. A digital signature method generally defines two complementary algorithms; one for signing and the other for verification, while the output of the signing process is called a digital signature. In this paper, we explain some consideration of The Digital Signature Algorithm (DSA). That is a United States Federal Government standard for digital signatures. It was proposed by the National Institute of Standards and Technology (NIST) in August 1991 for use in their Digital Signature Standard (DSS), specified in FIPS 186 [1], adopted in 1993. The DSA digital signature is a pair of large numbers represented in a computer as strings of binary digits. The digital signature is computed using a set of rules (i.e., the DSA) and a set of parameters such that the identity of the signatory and integrity of the data can be verified. Security of DSA 665