S/MIME APIs

The prototype IPP Encrypted Jobs and Documents v1.0 (TRUSTNOONE) specification sends sensitive IPP attributes and document data in S/MIME containers. Since this might be done with OpenSSL or GNU TLS, we need a CUPS API to expose this functionality.

• Function to convert an IPP attribute (1setOf text(MAX)) to a single string with newlines separating each value - this will allow X.509 certificates in attributes to be used.
• Function to convert a single string with newlines to an IPP attribute (1setOf text(MAX)) - necessary for servers to advertise their certificates and for clients to provide their certificate.
• Function to write an encrypted S/MIME container with attributes, file, X.509 certificate, and optional password
• Function to read an encrypted S/MIME container using a private key and optional password, producing attributes and an optional file (preferably with a callback vs. writing directly to disk)

The read/write functions should support the typical IO callback (like the IPP functions do).