DigitalSignatureSample.cs

using System.IO;
using OfficeOpenXml;
using OfficeOpenXml.Drawing;
using OfficeOpenXml.DigitalSignatures;
using System.Security.Cryptography.X509Certificates;

namespace EPPlusSamples.EncryptionProtectionAndVba
{
    public static class DigitalSignatureSample
    {
        public static void Run()
        {
            //Sign wb with minimal details.
            SignWorkbookSimple();
            //Sign wb with details such as commitment type, title and address
            SignWorkbookWithDetails();
            //How to create and add setup to a signatureline
            CreateSignatureline();
            //How to sign one or multiple signatureLines using Epplus
            SignSignatureLines();
        }

        private static void SignWorkbookSimple()
        {
            using(var pck = new ExcelPackage())
            {
                var wb = pck.Workbook;
                var ws = wb.Worksheets.Add("SomeWorksheet");

                //A digital signature requires a certificate with a private key.
                //In this case we'll sign with a certificate stored in a .pfx file.
                //In a real production environment, make to store your certificate in a secure way.
                var certFile = FileUtil.GetFileInfo("08-Encryption Protection and VBA\\02-VBA", "SampleCertificate.pfx");
                var cert = new X509Certificate2(certFile.FullName, "EPPlus");

                //Add a digital signature and sign it with the certificate
                var digitalSignature = wb.DigitalSignatures.Add(cert);

                //It is recommended to set a more secure digestmethod. As default is SHA-1.
                digitalSignature.SetDigestMethod(DigitalSignatureHashAlgorithm.SHA512);

                FileInfo fi = FileUtil.GetCleanFileInfo("8.3-01-SignWorkbook.xlsx");
                pck.SaveAs(fi);

                // Note: Because this is a test certificate, it will count as a 'recoverable' signature
                // unless you choose to trust the certificate.
                // If you add your own certificate it should count as a 'valid' signature.
            }
        }

        private static X509Certificate2 GetCert()
        {
            var certFile = FileUtil.GetFileInfo("08-Encryption Protection and VBA\\02-VBA", "SampleCertificate.pfx");

            //Excel lists different certificates for you.
            //You should be able to access the same list like this:
            //X509Store store = new X509Store(StoreLocation.CurrentUser);
            //store.Open(OpenFlags.ReadOnly);
            //var certAlt = store.Certificates[0];

            //If it doesn't work please double-check that you have certificates stored correctly
            //and double check the .net X509Store implementation for your OS

            return new X509Certificate2(certFile.FullName, "EPPlus");
        }

        private static void SignWorkbookWithDetails()
        {
            using (var pck = new ExcelPackage(FileUtil.GetCleanFileInfo("8.3-02-SigningDetails.xlsx")))
            {
                var wb = pck.Workbook;
                var ws = wb.Worksheets.Add("DetailsWs");

                //Same as above sample
                var cert = GetCert();

                //The method to add a signature also includes optional parameters for the comments commitment type and reason for signing
                //That represent the 'commitment type' and 'purpose for signing this document' fields from Excel.
                var digitalSignature = wb.DigitalSignatures.Add(cert);

                digitalSignature.CommitmentTyping = CommitmentType.Approved;
                digitalSignature.PurposeForSigning = "My reason for signing";

                //You can also add signer details via the Details property.
                //This represents the 'details' button in excel for example:
                var details = digitalSignature.Details;

                details.SignerRoleTitle = "Developer";
                details.Address1 = "ExampleStreet 2";
                details.Address2 = "Floor 2";
                details.ZipOrPostalCode = "114 51";
                details.City = "Stockholm";
                details.CountryOrRegion = "Sweden";
                details.StateOrProvince = "Stockholm";

                //The signature xml is not truly created until after the file has been saved
                bool isTheSignatureValid = digitalSignature.IsValid;
                pck.Save();

                //And so won't be valid until after save:
                bool signatureIsValid = digitalSignature.IsValid;
            }
        }


        private static void CreateSignatureline()
        {
            using (var pck = new ExcelPackage(FileUtil.GetCleanFileInfo("8.3-03-CreateSignatureLine.xlsx")))
            {
                var wb = pck.Workbook;
                var ws = wb.Worksheets.Add("SignatureLinesEmpty");

                //From a worksheet you can create a signatureline
                //A visual representation via a vmldrawing object for signing.
                var signatureLine = ws.SignatureLines.Add();

                //As in excel, you can set a few options for a suggested signer.
                signatureLine.Signer = "FirstName LastName";
                signatureLine.Title = "Engineer";
                signatureLine.Email = "FirstName@epplussoftware.com";
                signatureLine.SigningInstructions = "Please mr.LastName check and approve this document.";
                signatureLine.AllowComments = true;
                signatureLine.ShowSignDate = false;

                //You can set the size and position of a signatureline via from and to for columns and rows.
                signatureLine.From.Column = 5;
                signatureLine.To.Column = 9;
                signatureLine.From.Row = 0;
                signatureLine.To.Row = 6;

                //If opened in Excel someone can now double-click and sign this signatureline.
                pck.Save();
            }
        }

        private static void SignSignatureLines()
        {
            //Open package from previous sample
            using (var pck = new ExcelPackage(FileUtil.GetFileInfo("8.3-03-CreateSignatureLine.xlsx")))
            {
                var wb = pck.Workbook;
                var ws = wb.Worksheets[0];

                ws.Name = "SignedWorksheet";

                var cert = GetCert();

                var signatureLine = ws.SignatureLines[0];

                //Sign the signature line from the previous sample
                signatureLine.AsSignatureLine.SignWithText(cert, "FirstName LastName");

                //The reason for '.AsSignatureline' is because Signature Line is actually a child-class.
                //The parent class is SignatureLineStamp A signatureLineStamp can only be signed with an image and has a different look
                //Let's add one and sign that too
                var stamp = ws.SignatureLines.AddStamp();

                stamp.Signer = "FirstName LastName";
                stamp.Title = "Engineer";

                //Note that only .bmp fileformat are supported for digital signatures
                var sampleImage = FileUtil.GetFileInfo("08-Encryption Protection and VBA\\03-DigitalSignatures", "SignatureImgExample.bmp");
                var image = new ExcelImage(sampleImage);
                stamp.SignWithImage(cert, image);


                //Stamps can also be resized and moved
                stamp.From.Column = 2;
                stamp.To.Column = 4;
                stamp.From.Row = 8;
                stamp.To.Row = 17;

                //Naturally a non-stamp can also be signed with an image.
                //Let's add one so we can see all variations.
                var SignatureLineTwo = ws.SignatureLines.Add();
                SignatureLineTwo.SignWithImage(cert, image);
                
                pck.SaveAs(FileUtil.GetCleanFileInfo("8.3-04-SignSignatureLines.xlsx"));
            }
        }
    }
}