http://www.rfc-editor.org/rfc/rfc5958.txt
RFC 5958: Asymmetric Key Packages, S. Turner2010-08-01T23:00:00-00:00This document defines the syntax for private-key information and a content type for it. Private-key information includes a private key for a specified public-key algorithm and a set of attributes. The Cryptographic Message Syntax (CMS), as defined in RFC 5652, can be used to digitally sign, digest, authenticate, or encrypt the asymmetric key format content type. This document obsoletes RFC 5208. [STANDARDS-TRACK]