University of Texas at Austin Department of Computer Sciences
Networking Research Laboratory
Department of Computer Sciences
The University of Texas at Austin

Director: Simon S. Lam (more publications)

The first secure sockets layer: SNP preceded SSL by several years


Secure sockets layers (SSL followed by TLS) have played a crucial role in securing client-server communications for enabling e-commerce as well as for other Internet applications (e.g.,  gmail).  My research group designed and built the first secure sockets layer, SNP, in 1993 more than a year before Netscape (developer of SSL) was founded as a company.  SNP won the 2004 ACM Software System Award (past award winners include Unix, TCP/IP, and WWW).


Our work began in 1991 as a theoretical investigation on the formal meaning of a protocol layer satisfying an upper interface specification as a service provider and a lower interface specification as a service consumer [1]. We received a grant from the National Security Agency in June 1991 to investigate how to apply our theory of modules and interfaces to security verification [2].  At that time, there were three well-known authentication systems built (MIT's Kerberos) or being developed (DEC's SPX and IBM's KryptoKnight).  We recognized that all of these systems suffered from a common drawback, namely, they did not export a clean and easy-to-use interface that could be readily used by Internet applications.  For example, it would take a tremendous amount of effort to “kerberize” an existing distributed application.


Toward the goal of "secure network programming for the masses," we invented secure sockets as a high-level abstraction suitable for securing Internet applications.  In 1993, we designed and built a prototype of the first secure sockets layer, named Secure Network Programming (SNP).  SNP, designed as an application sublayer on top of sockets, provides a user interface closely resembling sockets.  This resemblance was by design so that security could be retrofitted into existing socket programs with only minor modifications.  Also, with such a sublayer carefully designed and its implementation thoroughly debugged, it can be easily used by any Internet application that uses sockets for end-to-end communications.  This is a natural idea in hindsight but, in 1993, it was novel and a major departure from mainstream network security research at that time.


SNP's secure sockets support both stream and datagram semantics with security guarantees (i.e., data origin authenticity, data destination authenticity, data integrity, and data confidentiality.)  Many of the ideas and design choices in SNP can be found in subsequent secure sockets layers (SSL and TLS), including: placing authenticated communication endpoints in the application layer, use of public key cryptography for authentication, a handshake protocol for establishing session state including a shared secret, use of symmetric key cryptography for data confidentiality, and managing contexts and credentials in the secure sockets layer.


We articulated the case for secure sockets in a paper presented on June 8, 1994 at the USENIX Summer Technical Conference [0].  We also presented our system design together with performance measurement results from our prototype implementation to clearly demonstrate the practicality of a secure sockets layer.  Netscape Communications which designed and implemented SSL was founded as a company in 1994 about the time when our USENIX paper was published.


Main publication


[0] Thomas Y. C. Woo, Raghuram Bindignavle, Shaowen Su, and Simon S. Lam, "SNP: An Interface for Secure Network Programming," Proceedings USENIX Summer Technical Conference, Boston, June 6-10, 1994; also available from .


Supporting work and grants


[1] Simon S. Lam and A. Udaya Shankar, “A Theory of Interfaces and Modules I — Composition Theorem,” IEEE Transactions on Software Engineering, Vol. 20, No. 1, January 1994.


[2] Simon S. Lam (PI/PD), "Applying a Theory of Modules and Interfaces to Security Verification," NSA INFOSEC University Research Program grant no. MDA 904-91-C-7046, 1991-94.


[3] Simon S. Lam (PI/PD), "A Proof Methodology for Authentication Protocols," NSA INFOSEC University Research Program grant no. MDA 904-93-C-4089, 1993-96.


[4] Thomas Y. C. Woo, Authentication and Authorization in Distributed Systems, Ph.D. Dissertation, Dept. of Computer Sciences, UT-Austin, August 1994 (supervisor: Simon S. Lam).


[5] Raghuram Bindignavle, Secure Network Programming, M.A. Thesis, Dept. of Computer Sciences, UT-Austin, December 1994 (supervisor: Simon S. Lam).