Research activity in 1998
The group's work in Security and Computer Network started in 1994, with special interest in public key systems as a basis for applications in secure wide area network communications. Since then, ten students have graduated with a thesis in network security, supervised by Prof. Bergadano. This activities continued until the present day, with significant collaboration with the University of Cambridge. This collaboration has included research on such issues as public key certification, innovative digital signature mechanisms, and WWW security. From 1994 until 1996, research activities in the area of secure agent architectures were investigated, in collaboration with Prof. Vita, at the University of Messina. In 1996, activities in computer security were also started, especially in the areas of password checking and intrusion detection. Other undergraduate theses are under completion in this area, also supervised by prof. Bergadano. On the other hand, in the wider area of computer networks, Prof. Sirovich has investigated the ISO/OSI protocols during the past ten years, with special reference to network management and directory services. Also with the participation of Prof. Balbo and his group, the activity in 1998 has included a project for the study and the implementation of secure multicast trasmission and video-conferencing.
a) Public key systems and certification
This research is concerned with public key certification in distributed environments, proposing a certification scheme to exchange documents that are digitally signed.
Certification is the weakest point of cryptographic and authentication systems based on public keys. Thus, it is the real condition for security in every kind of network transaction that has to be private and associated in an unambiguous way to a unique user. In fact, if the public key is associated to a person different from the legitimate owner, the system is compromised, and it is possible to read reserved messages and to prepare false digital signatures.
Certification avoids wrong associations of public keys. However, certification brings about a complex set of problems, made even more difficult by the possibility that the legitimate key pair owner loses his private key. For this reason the certification is at the base of almost all computer network security systems, and is treated explicitly by standards such as X.509. Our system, proposed in collaboration with the University of Cambridge, includes the implementation of a separate authority dedicated to delete the public key certificates that are no longer valid. Log file records are bound in a chain of hash values, so that they may not be deleted by the authority in an undetected way. The system has been implemented and a series of experiments is starting to integrate the above certification system with a few browser and mail services available on the market, both in Unix and Windows NT environments. Through this structure it will be possible to obtain a number of secure services that require signed and/or encrypted documents to be sent.
a.1) Secure Mailtools
In this research we studied PGP (Pretty Good Privacy), the most popular mail encryption and signature tool available worldwide. Within the context of two undergraduate theses, that were supervised by the security group, a public domain program, named "ACT", was implemented in 1997 and maintained in 1998. This tool is compatible with PGP (versions prior to 5.0), but solves some of its weaknesses.
a.2) Digital Signatures and Authentication [2]
The research was about the study of the mechanism to generate digital signatures based on public key algorithms. In collaboration with the University of Cambridge we made a new and alternative proposal to generate digital signatures based only on hash function chains. This mechanism turns out to be more efficient than the traditional approaches, and moreover it does not involve all the problems connected to the restrictions imposed by some countries about the export of encryption software.
b) Secure WWW [3,4]
The research is concerned with authentication and privacy in the World Wide Web. The security of the transactions is guaranteed using public key systems, together with the certification scheme described above. The implementation is based on the original HTTP protocol and on commercial browsers. It is obtained through Java applets associated to the client, that silently transform the base HTTP transaction into an exchange of encrypted and authenticated information. The actual communication is not carried out at the HTTP level, but between application processes that are added for this task, both on the client host and on the server. The idea is an alternative w.r.t. the SHTTP protocol, that modifies the standard HTTP format, and also w.r.t. SSL, that works at the level of the communication software. The advantage is a quicker integration with the pre-existent tools. We are finishing the implementation of a prototype that will be also used to address some of the aspects we study in the context of public key certification.
c) Password systems [1,5] and access control [6]
Another aspect of our research is related to the important problem of password checking. User passwords tend to be weak, and checking at the time of password creation or change is highly recommended. Although there are more sophisticated authentication systems - like those based on dedicated hardware (for instance a smartcard) or those asking for an answer to a "challenge" – the most common systems are based on passwords.
This as a consequence of their semplicity: they can be integrated in every environment without dedicated hardware and with well known user interfaces. In order to prevent bad password choices, the user passwrod is usually confronted with a dictionary, with implementation difficulties that are related to checking time and especially space to store the dictionary. We have developed a proactive password checking method that can lead to very high dictionary compression, with low error rates, under one per cent. On the basis of the classification alghorithm, the password checker ProCheck has been implemented as a patch for the Unix command passwd. ProCheck is freely distributed from http://maga.di.unito.it, and versions for SunOS, Ultrix and OSF1 are available. A version for NT has also been developed. The research is described in [1,5].
Within the same context, the research group is carrying out an extensive research to detect unauthorized accesses through the observation of user behavior. For several months, a few volunteers were monitored during their normal work at the computer.
Parameters such as log-in time, typing speed, executed commands, and so on, were gathered and stored for every user. A model of each user was then built from these parameters and used to classify further connections as "legal" or "illegal" (i.e. not originated by the owner of the account used in the connection). A 90% accuracy was achieved, on the average, in the classification of new connections within the first ten minutes of the log-in session [6].
d) The X.500 protocol Directory (Franco Sirovich)
The X.500 protocol directory allows to realize a sophisticated distributed database with a partial reproduction of the database. Substantially, it is a free scheme with research functions for the database content. In the 1992 standard from ISO and CCITT, the functionality of the X.500 service was extended introducing access control. Basic Access Control functionalities have been studied, and an algorithm was developed to verify at runtime the access control for a generic X.500 database.
A new interesting concept has originated from the research and development on Directories: The Concept of MetaDirectory.
A MetaDirectory is a controlled union of all the Directories of an Organisation, that on one side allows to have a single point of access to a common repository of data for the whole organisation, and on the other side allows to synchronise and the data contained in different data bases and to control the flow of data from one data base to another that is configured to receive the updates of the data from the "master" one. The interesting point is that the master ship is defined at the attribute level, and the values ofattributes can be obtained via an appropriate computation from one or moresource attributes.
We are going to experiment with these new concepts in tha area of controlled access to University data from web servers.
e) Network Management (Franco Sirovich)
With the development of applications on computer networks, the problem of managing complex network systems became more and more important. Both within ISO/ITU and Internet, specific protocols and informative models have been developed to realize a distributed system to handle both network elements and distributed network applications. The two network management models are not equivalent, even if a comparative study of them points out interesting analogies. Cryptographic key management in a security system for telecommunications is an interesting area to apply the management model and the corresponding OSI protocols.
An interesting problem tha is now being studied is the monitoring of Service Level Agreements. With the widespread adoption of outsourcing contract for the ITC services, the need has emerged of defining precisely the LEvel of Servce that the provider must offer to the Users. The finalisation of document called Service Level Agreement is considered to be expremely beneficial to the achievement of customer satisfaction. The problem is now that of being able to monitor le level of service that is being offered to group of Users and to be able to manage the resources of the ITC system so that the level of service defined in the SLA is actually met, thus avoiding that the users perceive a degradation of service.
MOnitoring Service LEvel Agreementsa is radically different than monitoring the performance of devices, computers, or telecommunication lines, because requires the measure of the service that is being delivered the actual users by applications, and not the service that the application "believes" is delivering to users. A Service Level Agreement Monitoring system must be able to allow the operators to identify the real causes of performance degradation, before the users perceive such a degradation and complain with the administrators.
f) Multicast Conferencing and Security (Davide Cavagnino)
The aim of this research is to study and apply security algorithms and techniques to the transmission of multimedia streams in a multicast environment. Multicast communications are gaining increasing interest in the Internet community, and more generally in broadcasting environments. Using multicasting it is possible to make an efficient use of network resources. Nonetheless, the use of multicasting poses new security problems, e.g., privacy of a communication among a set of users, protection from the illegal reproduction of the content of multimedia transmission (with the possibility of identification of the re-player), individual authentication with efficient cryptographic techniques, authorization of the sender in transmitting to a multicast group, billing of the service.
All these issues need efficient solutions, given that the management of some kinds of multimedia data (video and audio) is resource consuming, making it difficult to use classicalasymmetric techniques. Public key encryption and authentication (signatures) require a large computing power both on the receiving and sending sides. On the other hand, shared key solutions have obvious key distribution problems, and are not suitable for the authentication of the individual transmitting source in a group. We are experimenting novel security techniques with multicast software applications, and we are using tools where source code is freely available.
These tools comprise a session directory (for the announcement and reception of these announcements relative to multicast transmissions), a video conferencing tool, an audio tool, a shared whiteboard and a shared text editor. These applications are the most widely used in the MBone community.
To test the functionalities and the efficiency of the software tools, the Computer Science Department has been connected to the MBone (the Multicast Backbone), a network overlayed to the Internet with multicast capable islands connected by tunnels.
1998 Publications
[1] F. Bergadano, B. Crispo and G. Ruffo. "High dictionary compression with proactive password checking", ACM Transactions on Information and System Security (TISSEC), 1(1), pp 3-25, November 1998.
[2] R. Anderson, F. Bergadano, B. Crispo, J. Lee, C. Manifavas and R. Needham. "A New Family of Authentication Protocols",Operating Systems Review, 32(4 ):9-20, October 1998.
[3] F. Bergadano and P. De Mauro. "Third Party Certification of HTTP service access statistics", Cambrigde Int. Workshop on Security Protocols, Cambridge, UK, pp 95-107, April 1998.
[4] F. Bergadano, B. Crispo, M. Eccettuato. "Secure WWW Transactions using standard HTTP and Java applets", Third USENIX Workshop on Electronic Commerce, pages 109-120, Boston, Massachusetts, August 1998
[5] F. Bergadano, B. Crispo, G. Moretto and G. Ruffo. "Selezione preliminare di password in ambiente NT", Congresso AICA, pp 433-444, Novembre 1998
[6] F. Bergadano, D. Gunetti and G. Ruffo. Online Anomaly Detection in a Real Network Environment. Technical Report, 1997.
Software Products
Software Products developed or maintained in 1998 (distributed from http://maga.di.unito.it):
