Interoperability Characteristics of S/MIME Products

S/MIME is based upon the popular MIME standard, and describes a protocol for adding cryptographic security services through MIME encapsulation of digitally signed and encrypted objects. The S/MIME version 2 specification was designed to promote interoperable secure electronic mail. However, because the specification allows multiple interpretations and implementations, and is sometimes silent about key aspects that affect interoperability, a number of “S/MIME Enabled” products are available on the market that are incapable of fully interacting with one another. In this paper, we present a set of characteristics that affect the interoperability profile for a given S/MIME application, and illustrate how they may be used to achieve a higher level of interoperability within the family of S/MIME compliant products. We also analyze the S/MIME version 3 specification to determine what subset of the identified interoperability characteristics still remain to be adequately addressed.