Digitally sign .xlsx file using System.IO.Packaging in c#

Question

Greeings,

I am trying to digitally sign an excel file using System.IO.Packaging but I can't get this working.

The simplified code I am using is as follows:

var packageFile = @"C:\temp\test.xlsx";
var package = Package.Open(packageFile, FileMode.Open);
var packageDigitalSignatureManager = new PackageDigitalSignatureManager(package);
var uriCollection = package.GetParts().ToList().Select(part => part.Uri);
X509Certificate2 cert = new X509Certificate2(@"D:\certs\adrianganea.pfx", "password", X509KeyStorageFlags.Exportable);
var signature = packageDigitalSignatureManager.Sign(uriCollection, cert);

The document appears to be signed but the signature is not valid: Invalid Signatures

Any ideas?

Many thanks, Adrian

Answer 1

Nevermind, it seems that the signing certificate needs to be embedded: packageDigitalSignatureManager .CertificateOption =CertificateEmbeddingOption.InSignaturePart;

This link contains a good example.