VSIX: fix signature timestamp format string bug

src/Sign.Core/Tools/VsixSignTool/XmlSignatureBuilder.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE.txt file in the project root for more information.
 
+using System.Globalization;
 using System.Security.Cryptography.X509Certificates;
 using System.Security.Cryptography.Xml;
 using System.Xml;
@@ -226,7 +227,7 @@ public void SetFileManifest(OpcSignatureManifest manifest)
             var signatureTimeFormatElement = _document.CreateElement("Format", OpcKnownUris.XmlDigitalSignature.AbsoluteUri);
             var signatureTimeValueElement = _document.CreateElement("Value", OpcKnownUris.XmlDigitalSignature.AbsoluteUri);
             signatureTimeFormatElement.InnerText = "YYYY-MM-DDThh:mm:ss.sTZD";
-            signatureTimeValueElement.InnerText = _signingContext.ContextCreationTime.ToString("yyyy-MM-ddTHH:mm:ss.fzzz");
+            signatureTimeValueElement.InnerText = _signingContext.ContextCreationTime.ToString("yyyy-MM-ddTHH:mm:ss.fzzz", CultureInfo.InvariantCulture);
 
             signatureTimeElement.AppendChild(signatureTimeFormatElement);
             signatureTimeElement.AppendChild(signatureTimeValueElement);

test/Sign.Core.Test/Tools/VSIXSignTool/OpcPackageSigningTests.cs

@@ -2,8 +2,10 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE.txt file in the project root for more information.
 
+using System.Globalization;
 using System.Security.Cryptography;
 using System.Security.Cryptography.X509Certificates;
+using System.Xml;
 using Sign.Core.Timestamp;
 using Xunit.Abstractions;
 
@@ -220,6 +222,73 @@ public void ShouldRemoveSignature()
             }
         }
 
+        [Fact]
+        public void ShouldUseInvariantCultureForContextCreationTime()
+        {
+            CultureInfo originalCulture = CultureInfo.CurrentCulture;
+
+            try
+            {
+                // This test only works if the current culture is one of a set of cultures that includes en-DK that
+                // that repro the original bug.  However, because tests should not rely on a specific culture being
+                // installed, we'll create a custom culture just for this test.
+                var customCulture = (CultureInfo)CultureInfo.InvariantCulture.Clone();
+
+                customCulture.DateTimeFormat.TimeSeparator = ".";
+
+                CultureInfo.CurrentCulture = customCulture;
+
+                using (OpcPackage package = ShadowCopyPackage(
+                    SamplePackage,
+                    out string? path,
+                    OpcPackageFileMode.ReadWrite))
+                {
+                    OpcPackageSignatureBuilder signerBuilder = package.CreateSignatureBuilder();
+
+                    signerBuilder.EnqueueNamedPreset<VSIXSignatureBuilderPreset>();
+
+                    using (X509Certificate2 certificate = _pfxFilesFixture.GetPfx(
+                        keySizeInBits: 3072,
+                        HashAlgorithmName.SHA384))
+                    using (RSA? rsaPrivateKey = certificate.GetRSAPrivateKey())
+                    {
+                        OpcSignature signature = signerBuilder.Sign(
+                            new SignConfigurationSet(
+                                publicCertificate: certificate,
+                                signatureDigestAlgorithm: HashAlgorithmName.SHA384,
+                                fileDigestAlgorithm: HashAlgorithmName.SHA384,
+                                signingKey: rsaPrivateKey!));
+
+                        using (Stream stream = signature.Part!.Open())
+                        {
+                            XmlDocument document = new();
+
+                            document.Load(stream);
+
+                            XmlNode? signatureTimeValueElement = document.GetElementsByTagName("Value")[0];
+
+                            Assert.NotNull(signatureTimeValueElement);
+
+                            const string expectedFormat = "yyyy-MM-ddTHH:mm:ss.fzzz";
+
+                            bool isValidFormat = DateTimeOffset.TryParseExact(
+                                signatureTimeValueElement.InnerText,
+                                expectedFormat,
+                                CultureInfo.InvariantCulture,
+                                DateTimeStyles.None,
+                                out DateTimeOffset parsedDateTime);
+
+                            Assert.True(isValidFormat, $"The date time string '{signatureTimeValueElement.InnerText}' does not match the expected format '{expectedFormat}'.");
+                        }
+                    }
+                }
+            }
+            finally
+            {
+                CultureInfo.CurrentCulture = originalCulture;
+            }
+        }
+
         public static IEnumerable<object[]> RsaTimestampTheories
         {
             get
@@ -230,9 +299,9 @@ public static IEnumerable<object[]> RsaTimestampTheories
 
         private OpcPackage ShadowCopyPackage(string packagePath, out string path, OpcPackageFileMode mode = OpcPackageFileMode.Read)
         {
-            var temp = Path.GetTempFileName();
+            string temp = Path.GetTempFileName();
             _shadowFiles.Add(temp);
-            File.Copy(packagePath, temp, true);
+            File.Copy(packagePath, temp, overwrite: true);
             path = temp;
             return OpcPackage.Open(temp, mode);
         }