dotnet/wpf · error · System.Xml.XmlException

SR.RequiredTagNotFound (template: RequiredTagNotFound, arg…

Error message

SR.RequiredTagNotFound (template: RequiredTagNotFound, arg: signatureTimeTag)

What it means

The <SignatureTime> wrapper element itself was not found where the parser required it: ParseSignatureTimeTag throws XmlException with SR.Format(SR.RequiredTagNotFound, signatureTimeTag), i.e. 'Required tag <SignatureTime> not found'. This differs from corruption (5000-5003): the property content is missing the mandatory tag entirely.

Solutions

  1. Confirm the signature includes a <SignatureTime> SignatureProperty before asking for signing time (check Signature.SignedBy / properties collection)
  2. Re-sign with PackageDigitalSignatureManager.Sign, which emits the property automatically
  3. Fall back to parsing the embedded XML signature yourself if a non-WPF tool created it
  4. Skip signatures lacking the property rather than assuming they are corrupt

Example fix

// guard before reading
dynamic sig = packageSignatures[0];
if (!sig.IsCertificateExists || sig.SignatureProperties == null)
    return; // no SignatureTime property present
// then ParseSigningTime
Defensive patterns

Strategy: validation

Validate before calling

// Ensure a SignatureTime property exists before asking for the signing time
bool HasSignatureTime(System.IO.Packaging.PackageDigitalSignature sig)
{
    foreach (var rel in sig.SignaturePart.GetRelationships()) { /* signature properties present */ }
    var xml = new System.Xml.XmlDocument();
    xml.Load(sig.SignaturePart.GetStream());
    return xml.GetElementsByTagName("SignatureTime").Count > 0;
}

Try / catch

try { var t = GetSigningTime(sig); }
catch (XmlException ex) when (ex.Message.Contains("RequiredTagNotFound") || ex.Message.Contains("not found")) {
    return (signingTime: (DateTime?)null, trusted: false);
}

Prevention

When it happens

Trigger: ParseSigningTime -> ParseSignatureTimeTag invoked on a signature whose <SignatureProperty> lacks a <SignatureTime> element — e.g. a signature created without signature properties, or with properties signed under a different Object Id.

Common situations: Reading the signing time of signatures produced by external tools that do not emit the standard SignatureTime property; signatures where the Id/Value references point to the wrong property.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/4fb1531b22f60edf. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/WindowsBase/MS/Internal/IO/Packaging/XmlSignatureProperties.cs:315

                        && (reader.NodeType == XmlNodeType.EndElement))
                        {
                            //We must find a  </SignatureProperty> tag at this point, 
                            //else it could be that there are more SignatureTime or  
                            //other tags nested here and that is an error.
                            if (reader.Read()
                                && reader.MoveToContent() == XmlNodeType.EndElement
                                && string.Equals(signaturePropertyTag, reader.LocalName, StringComparison.Ordinal))
                                break;
                            else
                                throw new XmlException(SR.PackageSignatureCorruption);
                        }
                        else
                            // if we do not find the nested elements as expected
                            throw new XmlException(SR.PackageSignatureCorruption);
                }
            }
            else
                throw new XmlException(SR.Format(SR.RequiredTagNotFound, signatureTimeTag));


            // generate an equivalent DateTime object
            if (timeValue != null && timeFormat != null)
                return XmlFormattedTimeToDateTime(timeValue, timeFormat);
            else
                throw new XmlException(SR.PackageSignatureCorruption);
        }
        
        /// <summary>
        /// DateTime to XML Format
        /// </summary>
        /// <param name="dt">date time to convert</param>
        /// <param name="format">format to use - specified in DateTime syntax</param>
        /// <returns>opc-legal string suitable for embedding in XML digital signatures</returns>
        private static String DateTimeToXmlFormattedTime(DateTime dt, string format)
        {
            DateTimeFormatInfo formatter = new DateTimeFormatInfo

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