What Are S/MIME Messages?
Combinations of two separately defined formats
(1) MIME entities
(2) Cryptographic Message Syntax (CMS) objects
S/MIME entity formats
- one for enveloped (i.e., encrypted) – provides confidentiality and key distribution services
- two for signed – each provides integrity and data origin authentication services
- nested combinations of signed and encrypted formats
- may nest in any order to any “reasonable” depth
- multiple nesting is used to construct S/MIME Enhanced Security Services (details later)