生成具有特定命名空间前缀（“ds：”）的数字签名

Question

我对XML文件进行数字签名，但需要签名标记包含名称空间前缀“ds”。我在谷歌上搜索了一下，发现了很多同样的问题，但没有令人满意的答案。

我尝试将“ds”手动放入文件中，但签名变得无效。标记“SignatureValue”对标记“SignedInfo”进行签名，因此签名无效。

谁能告诉我如何生成标记“signaturevalue”的值，以便在添加前缀“ds”后替换签名？

Answer 1

显然很多人都遇到了同样的问题。在调查了类签名的源代码后，我得出结论，微软的目的是帮助我们。方法LoadXml（）中有硬编码的前缀“ds”。因此，可以生成签名，然后向其添加名称空间前缀“ds”，加载修改后的签名并重新计算“signaturevalue”。不幸的是，库中的bug使事情变得比需要的要难一些。下面是带有变通方法和注释的代码。

public static void SignXml(XmlDocument xmlDoc, X509Certificate2 cert)
{
        // transformation cert -> key omitted
        RSACryptoServiceProvider key;

        // Create a SignedXml object. 
        SignedXml signedXml = new SignedXml(xmlDoc);

        // Add the key to the SignedXml document. 
        signedXml.SigningKey = key;
        signedXml.SignedInfo.SignatureMethod = "http://www.w3.org/2001/04/xmldsig-more#rsa-sha256";
        signedXml.SignedInfo.CanonicalizationMethod = SignedXml.XmlDsigExcC14NTransformUrl;

        // Create a reference to be signed. 
        Reference reference = new Reference();
        reference.Uri = "#foo";
        reference.DigestMethod = "http://www.w3.org/2001/04/xmlenc#sha256";
        // Add an enveloped transformation to the reference. 
        reference.AddTransform(new XmlDsigEnvelopedSignatureTransform());
        reference.AddTransform(new XmlDsigExcC14NTransform());
        signedXml.AddReference(reference);

        KeyInfo keyInfo = new KeyInfo();
        KeyInfoX509Data keyInfoData = new KeyInfoX509Data();
        keyInfoData.AddIssuerSerial(cert.IssuerName.Format(false), cert.SerialNumber);
        keyInfo.AddClause(keyInfoData);
        signedXml.KeyInfo = keyInfo;

        // Compute the signature. 
        signedXml.ComputeSignature();

        // Add prefix "ds:" to signature
        XmlElement signature = signedXml.GetXml();
        SetPrefix("ds", signature);

        // Load modified signature back
        signedXml.LoadXml(signature);

        // this is workaround for overcoming a bug in the library
        signedXml.SignedInfo.References.Clear();

        // Recompute the signature
        signedXml.ComputeSignature();
        string recomputedSignature = Convert.ToBase64String(signedXml.SignatureValue);

        // Replace value of the signature with recomputed one
        ReplaceSignature(signature, recomputedSignature);

        // Append the signature to the XML document. 
        xmlDoc.DocumentElement.InsertAfter(xmlDoc.ImportNode(signature, true), xmlDoc.DocumentElement.FirstChild);
    }

    private static void SetPrefix(string prefix, XmlNode node)
    {
        node.Prefix = prefix;
        foreach (XmlNode n in node.ChildNodes)
        {
            SetPrefix(prefix, n);
        }
    }

    private static void ReplaceSignature(XmlElement signature, string newValue)
    {
        if (signature == null) throw new ArgumentNullException(nameof(signature));
        if (signature.OwnerDocument == null) throw new ArgumentException("No owner document", nameof(signature));

        XmlNamespaceManager nsm = new XmlNamespaceManager(signature.OwnerDocument.NameTable);
        nsm.AddNamespace("ds", SignedXml.XmlDsigNamespaceUrl);

        XmlNode signatureValue = signature.SelectSingleNode("ds:SignatureValue", nsm);
        if (signatureValue == null)
            throw new Exception("Signature does not contain 'ds:SignatureValue'");

        signatureValue.InnerXml = newValue;
    }