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Asked: 2026-05-11T03:05:42+00:00

The Windows SDK ships with a tool called signtool.exe that lets you sign a

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The Windows SDK ships with a tool called signtool.exe that lets you sign a file with a certificate. I need to do the same thing but in a background service so I’m on the lookout for a library (preferably managed code, but COM will do) to do the same thing. Any ideas?

Found the answer. Here’s how to use an X.509 certificate to sign a file in .NET:

CmsSigner signer = new CmsSigner(); signer.Certificate = new X509Certificate2(certificate);  SignedCms content = new SignedCms(new ContentInfo(File.ReadAllBytes(fileToSign))); content.ComputeSignature(signer, true); byte[] signedFile = content.Encode();  string signedFileName = fileToSign + '.signed'; File.WriteAllBytes(signedFileName, signedFile);  Console.WriteLine('Signed file: ' + signedFileName);

Here, certificate is the path to the .pfx file containing the certificate and fileToSign is the file to sign.

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  1. SignTool is using CAPICOM which is the COM wrapper for the Crypto API. You can use either one. If you’re going with CAPICOM, you can check the information here.

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