MimeMultipart smm = generateMultiPartRsa(SMIMESignedGenerator.DIGEST_SHA1, m);
SMIMESigned s = new SMIMESigned(smm);
verifySigners(s.getCertificatesAndCRLs("Collection", "BC"), s.getSignerInfos());
AttributeTable attr = ((SignerInformation)s.getSignerInfos().getSigners().iterator().next()).getSignedAttributes();
Attribute a = attr.get(CMSAttributes.messageDigest);
byte[] contentDigest = ASN1OctetString.getInstance(a.getAttrValues().getObjectAt(0)).getOctets();
mp = (MimeMultipart)m.getContent();
ContentType contentType = new ContentType(mp.getContentType());
String boundary = "--" + contentType.getParameter("boundary");