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The Kryptoknight Family of Light-Weight Protocols for Authentication and Key Distribution

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The Kryptoknight Family of Light-Weight Protocols for Authentication and Key Distribution IEEEJACMTRANSACTIONS ON NETWORKING, V(}L 3. NO. 1, FEBRUARY 1995 71 The KryptoKnight Family of Light-Weight Protocols for Authentication and Key Distribution Ray Bird, Inder Gopal, Fe//o)t, /EEE, Amir Herzberg, Phil Janson, Shay Kutten, Member, IEEE, Refik Molva, Member, IEEE, and Moti Yung Abstract— An essential function for achieving security in for performing the necessary authentication exchanges—these computer networks is reliable authentication of communicating keys may be secret keys shared by the involved parties if parties and network components. Such authentication typically symmetric cryptography is used, or public keys certified by relies on exchanges of cryptographic messages between the involved parties, which in turn implies that these parties be a trusted authority if asymmetric cryptography is used. The able to acquire shared seeret keys or certified public keys. issues of authentication and key distribution in the context of Provision of authentication and key distribution functions in the distributed applications have already been largely addressed primitive and msmwce-constrained environments of low-function by designs such as Kerberos 124] and X.509 [ 12]. networking mechanisms, portable, or wireless devices presents However, low-function networking mechanisms are typi- challenges in terms of resouree usage, system management, ease of use, etBciency, and flexibility that are beyond the capabilities cally subject to various environmental restrictions (e.g., small of previous designs such as Kerberos or X.509. packet header sizes, limited computing resources), which must This paper presents a family of light-weight authentication be taken into account when integrating security features. Such and key distribution protocols suitable for use in the low layers mechanisms must also accommodate various network config- of network architectures. All the protocols are built around a urations and connectivities (e.g., local area networks, wireless common two-way authentication protocol. The paper argues that key distribution may require substantially different approaches networks, global networks, etc. ) and devices of widely dif- in different network environments and shows that the proposed fering capabilities (e.g., palm-top, lap-top, desk-top, or floor- family of protocols offers a flexible palette of compatible standing devices). In such environments, the most primitive solutions addressing many different networking scenarios. component must be able to inter-operate securely with the most The mechanisms are minimal in cryptographic processing and powerful one, which implies the provision of simple common message size, yet they are strong enough to meet the needs of security functions to meet minimal needs. Getting essential secure key distribution for network entity authentication. Tbe protocols presented have been implemented as part authentication and key distribution functions to work within of a comprehensive security subsystem prototype called the resource restrictions of such low-function networking KryptoKnight, whose software and implementation aspeets environments presents challenges in terms of resource usage, are discussed in [16], and which is the basis for the recently efficiency, ease of use, flexibility, and system management. announced IBM Network Seeurity Program product. These issues are the subject of the present paper. The paper explains why existing key distribution designs, 1. INTROD(JCTION aimed at distributed application environments, are not suitable HE STEADILY growing use of computer networks is for use in low-function devices and network protocols. Instead T fostering increasing concerns about network security. One the paper proposes a Family of light-weight, authenticated of the main issues is effective control of access to network key distribution protocols that are especially suited for use in components and resources by expanding populations of users, such restricted environments. (The proposed protocols could some of which cannot always be trusted to use the network also be used at the application layer, although their intrinsic properly. An essential requirement for implementing suitable economy may lack some of the functional features often access controls is a mechanism for reliable authentication of desired in distributed applications. ) The pdper finally argues communicating entities and network users. that key distribution may require different approaches (e.g., State-of-the-art authentication protocols typically rely on communication patterns ) in different network environments exchanges of cryptographic messages between entities want- and it shows that the proposed family of protocols offers ing to authenticate one another prior to or during actual a flexible palette of compatible solutions addressing many communication. Such exchanges in turn demand that the possible cases, communicating parties be able to acquire cryptographic keys 11. BACKGROUND AND RELATED WORK Manuscript received December 7, 1992: revised May i 8, 1993 and June 30. 1993: approved by IEEE/ACM TRANSACTIONSON NETWORKINGEditor S, Lam. R. Bird i, wi[hIBM ~orpora(nr, Research Triangle Park, NC 27709 USA. A. Key Di.~tribution—E.xisting Designs and Limitations 1. ~opal, A. Hcrzberg, S. Kutwn, iurd M, Yung are with IBM T, J. Watson Rewarch Center, Yorktown Height\, NY 10598 USA, In a large network with tens, hundreds, or thousands of t? Jansrm is with IBM Zurich Research Laboratory, 8803 Ruschlikun, switching nodes and server computers, and several orders of Swit~erlimd (e-m~il: pj@~zurich.ihm.tom). R. Moivu ik WId~lns(itut Eurecwm, 06903 Soph]a-Antipolis, France. magnitude more client workstations and users, the problem of IEEE I.og Number 9408394. the distribution and safe-keeping of cryptographic keys is not 1063-6692/95$04.00 O 1995 IEEE 32 IEEWACM TRANSACTIONS ON NETWORKING, VOL. 3, NO. 1, FEBRUARY 1995 trivial. It is complex enough that one must abandon right away A 0 the idea of casual (manual) distribution procedures outside the system. Automated techniques based on electronic exchanges A, B, Na over the network are required. (1) b Several schemes have been designed for automating key distribution services in distributed systems, e.g., [18], [7], [1], [19], [2 1], [14], [20]. Some of these have lead to notable B, A, Nb, MACba(Na, Nb, B) implementations or standards, e.g., the Kerberos [24] and (2) + ANSI X9. 17 [11] schemes, which use DES technology, or the ISO-CCITT X.509 Directory Authentication scheme [12], A, B, MACab(Na, Nb) which relies on public key technology. These schemes vary in (3) F popularity. Kerberos is the basis for the security component provided by the Open Software Foundation (OSFTM) as part Fig. 1. Secure two-way authentication protocol. of its Distributed Computing Environment (DCE) product. However the authentication and key distribution protocols especially where public-key cryptography is used. Simpler defined by these designs are targeted at distributed application protocols can and indeed have been designed. However, while environments, and thus present a number of features that simplicity may give the illusion of security, it is in fact hard to make their use cumbersome or undesirable in more primitive achieve. In [5], [6], we introduced a family of authentication environments such as low-function link, network, or transport protocols that are at the same time efficient in message size and protocols, or remote booting protocols. computation overhead, and resistant to a wide set of attacks Yet authentication and key distribution functions are also known as interleaving attacks. The basic idea for formally required within lower-function layers. For instance, most wire- proving the correctness of these and similar protocols was less link protocols (e.g., CDPD, GSM) rely on such functions discussed initially in [5], while extension and full exploitation to assert the identity of a calling mobile device (though of the concept were developed in [9] and [2], after the work key distribution designs are rather primitive and not very reported here was completed. The formal proof concludes secure); similar functions can and have been built into X.25 that a successful attack would require directly breaking the packet layer implementations to restrict incoming calls to underlying encryption mechanism (which is assumed to be certain identified calling addresses; LAN adapter-based boot- impractical). This proof is not discussed further in the current ing protocols would also need such functions to prevent paper. booting from untrusted boot servers. Thus, in contrast to One of the protocols derived from that work is represented the existing application-layer designs, our goal here is to in Fig. 1. In this figure, the letters A and B stand for the design light-weight key distribution protocols that require min- identifiers of two network entities performing two-way au- imal computing resources from their environment. A common thentication. The variables Na and Nb are one-time random authentication protocol that has been tested against a wide numbers (called nonces) used by each party to challenge the range of attacks, called interleaving attacks, serves as the other to prove its identity. The notations MACba and MACab foundation for the entire family of key distribution protocols. denote cryptographic one-way hash functions, called Message It is described in the following section. Authentication Codes, computed with keys Kba and Kab respectively, and used to guarantee the authenticity
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