Support PKCS#7 definition for ContentType content ANY

[cconlon]

Description

This PR adds support to wolfCrypt's PKCS#7 to support the older PKCS#7 RFC (RFC 2315) encoding of the SignedData ContentInfo content as ANY. The newer CMS RFC (RFC 5652) defines that the content will be wrapped in an OCTET STRING, which our code was assuming would be the case.

PKCS#7 RFC 2315 definition of SignedData ContentInfo:

ContentInfo ::= SEQUENCE {
  contentType ContentType,
  content
    [0] EXPLICIT ANY DEFINED BY contentType OPTIONAL }

CMS RFC 5652 definition of the same thing:

EncapsulatedContentInfo ::= SEQUENCE {
  eContentType ContentType,
  eContent [0] EXPLICIT OCTET STRING OPTIONAL }

Related to ZD #16645.

Testing

Tested using customer PKCS#7 SignedData bundle, fed into wolfCrypt's PKCS#7 routines using the sample app being added to our wolfssl-examples repository: wolfSSL/wolfssl-examples#400

Checklist

• added tests
• updated/added doxygen
• updated appropriate READMEs
• Updated manual and documentation

[cconlon]

Retest this please

[JacobBarthelmeh]

Thanks Chris, tested it against the known bundle. Looks good.