public static SafeCryptMsgHandle CreateCryptMsgHandleToEncode(CmsRecipientCollection recipients, Oid innerContentType, AlgorithmIdentifier contentEncryptionAlgorithm, X509Certificate2Collection originatorCerts, CryptographicAttributeObjectCollection unprotectedAttributes)
{
using (HeapBlockRetainer hb = new HeapBlockRetainer())
{
// Deep copy the CmsRecipients (and especially their underlying X509Certificate2 objects). This will prevent malicious callers from altering them or disposing them while we're performing
// unsafe memory crawling inside them.
recipients = recipients.DeepCopy();
// We must keep all the certificates inside recipients alive until the call to CryptMsgOpenToEncode() finishes. The CMSG_ENVELOPED_ENCODE_INFO* structure we passed to it
// contains direct pointers to memory owned by the CERT_INFO memory block whose lifetime is that of the certificate.
hb.KeepAlive(recipients);
unsafe
{
CMSG_ENVELOPED_ENCODE_INFO *pEnvelopedEncodeInfo = CreateCmsEnvelopedEncodeInfo(recipients, contentEncryptionAlgorithm, originatorCerts, unprotectedAttributes, hb);
SafeCryptMsgHandle hCryptMsg = Interop.Crypt32.CryptMsgOpenToEncode(MsgEncodingType.All, 0, CryptMsgType.CMSG_ENVELOPED, pEnvelopedEncodeInfo, innerContentType.Value, IntPtr.Zero);
if (hCryptMsg == null || hCryptMsg.IsInvalid)
{
throw Marshal.GetLastWin32Error().ToCryptographicException();
}
return(hCryptMsg);
}
}
}
