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Vol: 53(67) No: 4 / December 2008 On the Security of Some Authentication Mechanisms from Windows Bogdan Groza Politehnica University of Timisoara, Faculty of Automatics and Computers, Timisoara, Romania, e-mail: bogdan.groza@aut.upt.ro, web: http://www.aut.upt.ro/~bgroza/ Andrei Alexandroni Pensive S.A., Brussels, Belgium, e-mail: andrei@pensive.eu Ioan Silea Politehnica University of Timisoara, Faculty of Automatics and Computers, Timisoara, Romania, e-mail: ioan.silea@aut.upt.ro, web: http://www.aut.upt.ro/~isilea/ Victor-Valeriu Patriciu Military Technical Academy, Department of Computer Engineering, Bucharest, Romania, e-mail: vip@mta.ro, web: http://www.mta.ro/conducere/victor_patriciu.php Keywords: authentication, cryptography, NTLM, protocol Abstract The paper investigates some authentication mechanisms used in Windows. In particular, the NTLM authentication protocol, which is commonly used in several solutions from Microsoft, is analyzed. The NTLM authentication is completely unsafe in several variants of use and some of its weaknesses previously known. A critical analysis is done, the weaknesses are explained and the safe solutions are underlined. As a practical example it is shown how the NTLM authentication from SharePoint based portals can be exploited to steal passwords and how to configure the NTLM for a safe use. This analysis is relevant as SharePoint becomes widely used and NTLM is still the default option and the only authentication mechanism available when there is no support for Kerberos. Nevertheless, a comparison between the password based authentication from UNIX and Windows OS is done. References [1] M. Bellare, R. Canetti, H. Krawczyk, “Keying Hash Functions for Message Authentication”, Advances in Cryptology – CRYPTO 96, LNCS vol. 1109, Springer-Verlag, 1996. [2] E. Biham, A. 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