public static byte[] SignMessage(byte[] data)
        {
            X509Store store = new X509Store(StoreLocation.CurrentUser);
            store.Open(OpenFlags.ReadOnly);
            X509Certificate2 certificate = null;
            //manually chose the certificate in the store
            X509Certificate2Collection sel = X509Certificate2UI.SelectFromCollection(store.Certificates, null, null, X509SelectionFlag.SingleSelection);

            if (sel.Count > 0)
            {
                certificate = sel[0];

                if (data == null)
                    throw new ArgumentNullException("data");
                if (certificate == null)
                    throw new ArgumentNullException("certificate");

                // Вычисляем подпись
                ContentInfo contentInfo = new ContentInfo(data);
                SignedCms signedCms = new SignedCms(contentInfo, true);
                CmsSigner cmsSigner = new CmsSigner(certificate);
                cmsSigner.IncludeOption = X509IncludeOption.EndCertOnly;
                signedCms.ComputeSignature(cmsSigner, false);
                byte[] pk = signedCms.Encode();
                return pk;
            }
            return null;
        }