The following flags can be passed in the flags parameter.
If CMS_DETACHED is set then cleartext signing will be used, this option only
makes sense for SignedData where CMS_DETACHED is also set when CMS_sign() is
If the CMS_TEXT flag is set MIME headers for type text/plain are added to
the content, this only makes sense if CMS_DETACHED is also set.
If the CMS_STREAM flag is set streaming is performed. This flag should only
be set if CMS_STREAM was also set in the previous call to a CMS_ContentInfo
If cleartext signing is being used and CMS_STREAM not set then the data must
be read twice: once to compute the signature in CMS_sign() and once to output
the S/MIME message.
If streaming is performed the content is output in BER format using indefinite
length constructed encoding except in the case of signed data with detached
content where the content is absent and DER format is used.