ASN1EncodableVector signedAttrs = generateSignedAttributes();
SMIMESignedGenerator gen = new SMIMESignedGenerator();
gen.addSigner(origKP.getPrivate(), origCert, SMIMESignedGenerator.DIGEST_SHA256, new AttributeTable(signedAttrs), null);
gen.addCertificatesAndCRLs(certs);
MimeMultipart smm = gen.generate(mp, "BC");
File tmpFile = File.createTempFile("bcTest", ".mime");
MimeMessage msg = createMimeMessage(tmpFile, smm);