How to validate authenticode for Javascript in C#

Question

I was able to sign a js file with PowerShell Set-AuthenticodeSignature. After that i can see signature appeared in file in form of:

// SIG // Begin signature block
// SIG // MIIKgAYJKoZIhvcNAQcCoIIKcTCCCm0CAQExCzAJBgUr
// SIG // ....
// SIG // End signature block

I can validate signature using Get-AuthenticodeSignature. It says that sig is valid, but I cant find a way to validate signature in C# code. All of those options failed:

1. X509Certificate.CreateFromSignedFile
2. X509Certificate object c# performance and memory issues alternative – fixed
3. Used WinVerifyTrust from Wintrust.dll
4. Ported part of Get-AuthenticodeSignature from PowerShell!

Maybe there are some specific apis to validate js signatures?

Answer 1

WinVerifyTrust supports verifying files other than executables using the WTD_CHOICE_BLOB flag. Make sure you provide the WINTRUST_BLOB_INFO struct with the correct subject interface package (SIP). From what I can see, Get-AuthenticodeSignature command uses the PowerShell SIP {603bcc1f-4b59-4e08-b724-d2c6297ef351} to verify the signature. I assume Set-AuthenticodeSignature uses the same SIP to sign the script.

Answer 2

I recently encountered similar problem and let me show what I did to solve this problem. Before I go , there are few assumptions I make now. Please correct me if I am wrong.

1. wintrust is working for all other cases other than script files like .js or .vbs
2. You might have attempted "wintrustverify" from an console application (C#)

I figured it out this happens only with script files as I have mentioned above because wintrust behaves wierdly when its methods are being executed from free-threaded apartment model (MTA). Once it's been wrapped inside a STA thread, it started working for me. Later I came to know it is a historical issue that we should have taken a precaution when we deal with any COM components interoperations from .Net application.

Here is the code snippet, you can replace the verifysignature with your wintrust code logic and try. I hope this helps.

            public static void CheckSignature()
            {
                STAApartment apt = new STAApartment();
                var result = apt.Invoke(() =>
                {
                    return VerifySignature(@".\signedjsfile.js", false);
                });
                Console.WriteLine(result);
            }

            private static WinVerifyTrustResult VerifySignature(string filePath, bool verifySignatureOnly)
            {

                using (var wtd = new WinTrustData(new WinTrustFileInfo(filePath))
                {
                    dwUIChoice = WintrustUIChoice.WTD_UI_NONE,
                    dwUIContext = WinTrustDataUIContext.WTD_DATA_UI_EXECUTE,
                    fdwRevocationChecks = WinTrustDataRevocationChecks.WTD_REVOCATION_CHECK_WHOLECHAIN,
                    dwStateAction = WintrustAction.WTD_STATEACTION_IGNORE,
                    dwProvFlags = verifySignatureOnly ? WintrustProviderFlags.WTD_HASH_ONLY_FLAG : WintrustProviderFlags.WTD_REVOCATION_CHECK_CHAIN
                })
                {
                    var result = WinTrust.WinVerifyTrust(
                        WinTrust.INVALID_HANDLE_VALUE, new Guid(WinTrust.WINTRUST_ACTION_GENERIC_VERIFY_V2), wtd
                    );
                    return result;
                }
            }

            public class STAApartment
            {
                public T Invoke<T>(Func<T> func)
                {
                    var tcs = new TaskCompletionSource<T>();
                    Thread thread = new Thread(() =>
                    {
                        try
                        {
                            tcs.SetResult(func());
                        }
                        catch (Exception e)
                        {
                            tcs.SetException(e);
                        }
                    });
                    thread.SetApartmentState(ApartmentState.STA);
                    thread.Start();                
                    return tcs.Task.Result;
                }
            }