生成数字签名但具有特定的命名空间前缀 ("ds:")

Question

我对 XML 个文件进行了数字签名，但需要签名标签包含命名空间前缀 "ds"。我研究了很多 google 并发现了很多相同的问题，但没有令人满意的答案。

我试图将 "ds" 手动放入文件中，但签名无效。标签 "SignatureValue" 对标签 "SignedInfo" 进行签名，因此签名无效。

有人可以告诉我如何生成标签 "SignatureValue" 的值以便我可以在添加前缀 "ds" 后替换签名吗？

Answer 1

编辑： 你可以看到这个 post 在我的另一个答案中提到的算法。

假设如果不编写自己的算法就无法对文档进行规范化和签名，则可能的解决方法是 "inject" 签名后在签名元素上添加命名空间前缀，然后将其从他们在验证之前。

例如：

void SignXml(XmlDocument xmlDoc, RSA Key)
{
    SignedXml signedXml = new SignedXml(xmlDoc);
    signedXml.SigningKey = Key;

    Reference reference = new Reference("");
    reference.AddTransform(new XmlDsigEnvelopedSignatureTransform());

    signedXml.AddReference(reference);

    signedXml.ComputeSignature();

    XmlElement xmlSignature = signedXml.GetXml();

    //Here we set the namespace prefix on the signature element and all child elements to "ds", invalidating the signature.
    AssignNameSpacePrefixToElementTree(xmlSignature, "ds");

    xmlDoc.DocumentElement.AppendChild(xmlDoc.ImportNode(xmlSignature, true));
}

bool VerifyXmlSignature(XmlDocument xmlDoc, RSA Key, string prefix)
{
    SignedXml signedXml = new SignedXml(xmlDoc);

    //Get the <ds:Signature /> element
    XmlElement xmlSignature = (XmlElement)xmlDoc.GetElementsByTagName(prefix + ":Signature")[0];

    //Undo what we did after signing
    AssignNameSpacePrefixToElementTree(xmlSignature, "");

    //Now it will pass verification.
    signedXml.LoadXml(xmlSignature);
    return signedXml.CheckSignature(Key);
}

void AssignNameSpacePrefixToElementTree(XmlElement element, string prefix)
{
    element.Prefix = prefix;

    foreach (var child in element.ChildNodes)
    {
        if (child is XmlElement)
            AssignNameSpacePrefixToElementTree(child as XmlElement, prefix);
    }
}

Answer 2

由于您是签署文件的人，这应该很容易做到，但是 System.Security.Cryptography.Xml 中的 class 并不真正支持这一点。

如果您只需要为 Signature 元素添加前缀，那么前提是 Signature 本身未被引用（或者如果它是被引用元素的一部分，那么只要通过转换将其删除，如“http://www.w3.org/2000/09/xmldsig#enveloped-signature") 那么您需要做的就是根据更改后的 SignedInfo 元素重新计算 SignatureValue。有关示例，请参见下面的 SignEnveloped 方法。

但是，您的签名不会通过 MSDN's How to: Verify the Digital Signatures of XML Documents 中概述的验证，因为 SignedXml class 似乎生成一个新的没有前缀元素。下面的 class 解决了看似错误的 SignedXmls 实现，但在其他不需要前缀元素的框架中也可能存在验证问题。

public static class XmlSigning
{
    private static Type tSignedXml = typeof(SignedXml);
    private static ResourceManager SecurityResources = new ResourceManager("system.security", tSignedXml.Assembly);

    //these methods from the SignedXml class still work with prefixed Signature elements, but they are private
    private static ParameterExpression thisSignedXmlParam = Expression.Parameter(tSignedXml);
    private static Func<SignedXml, bool> CheckSignatureFormat
        = Expression.Lambda<Func<SignedXml, bool>>(
            Expression.Call(thisSignedXmlParam, tSignedXml.GetMethod("CheckSignatureFormat", BindingFlags.NonPublic | BindingFlags.Instance)),
            thisSignedXmlParam).Compile();
    private static Func<SignedXml, bool> CheckDigestedReferences
        = Expression.Lambda<Func<SignedXml, bool>>(
            Expression.Call(thisSignedXmlParam, tSignedXml.GetMethod("CheckDigestedReferences", BindingFlags.NonPublic | BindingFlags.Instance)),
            thisSignedXmlParam).Compile();

    public static void SignEnveloped(XmlDocument xmlDoc, RSACryptoServiceProvider key, string signatureNamespacePrefix)
    {
        SignedXml signedXml = new SignedXml(xmlDoc);
        signedXml.SigningKey = key;

        Reference reference = new Reference("");
        reference.AddTransform(new XmlDsigEnvelopedSignatureTransform());

        signedXml.AddReference(reference);

        signedXml.ComputeSignature();

        XmlElement xmlSignature = signedXml.GetXml();

        if (!string.IsNullOrEmpty(signatureNamespacePrefix))
        {
            //Here we set the namespace prefix on the signature element and all child elements to "ds", invalidating the signature.
            AssignNameSpacePrefixToElementTree(xmlSignature, "ds");

            //So let's recompute the SignatureValue based on our new SignatureInfo...

            //For XPath
            XmlNamespaceManager namespaceManager = new XmlNamespaceManager(xmlDoc.NameTable);
            namespaceManager.AddNamespace("ds", "http://www.w3.org/2000/09/xmldsig#"); //this prefix is arbitrary and used only for XPath

            XmlElement xmlSignedInfo = xmlSignature.SelectSingleNode("ds:SignedInfo", namespaceManager) as XmlElement;

            //Canonicalize the SignedInfo element
            XmlDsigC14NTransform transform = new XmlDsigC14NTransform();
            XmlDocument signedInfoDoc = new XmlDocument();
            signedInfoDoc.LoadXml(xmlSignedInfo.OuterXml);
            transform.LoadInput(signedInfoDoc);

            //Compute the new SignatureValue
            string signatureValue = Convert.ToBase64String(key.SignData(transform.GetOutput() as MemoryStream, new SHA1CryptoServiceProvider()));
            //Set it in the xml
            XmlElement xmlSignatureValue = xmlSignature.SelectSingleNode("ds:SignatureValue", namespaceManager) as XmlElement;
            xmlSignatureValue.InnerText = signatureValue;
        }

        xmlDoc.DocumentElement.AppendChild(xmlDoc.ImportNode(xmlSignature, true));
    }

    public static bool CheckSignature(XmlDocument xmlDoc, RSACryptoServiceProvider key)
    {
        if (key == null)
            throw new ArgumentNullException("key");

        SignedXml signedXml = new SignedXml(xmlDoc);

        //For XPath
        XmlNamespaceManager namespaceManager = new XmlNamespaceManager(xmlDoc.NameTable);
        namespaceManager.AddNamespace("ds", "http://www.w3.org/2000/09/xmldsig#"); //this prefix is arbitrary and used only for XPath

        XmlElement xmlSignature = xmlDoc.SelectSingleNode("//ds:Signature", namespaceManager) as XmlElement;

        signedXml.LoadXml(xmlSignature);

        //These are the three methods called in SignedXml's CheckSignature method, but the built-in CheckSignedInfo will not validate prefixed Signature elements
        return CheckSignatureFormat(signedXml) && CheckDigestedReferences(signedXml) && CheckSignedInfo(signedXml, key);
    }

    private static bool CheckSignedInfo(SignedXml signedXml, AsymmetricAlgorithm key)
    {
        //Copied from reflected System.Security.Cryptography.Xml.SignedXml
        SignatureDescription signatureDescription = CryptoConfig.CreateFromName(signedXml.SignatureMethod) as SignatureDescription;
        if (signatureDescription == null)
            throw new CryptographicException(SecurityResources.GetString("Cryptography_Xml_SignatureDescriptionNotCreated"));

        Type type = Type.GetType(signatureDescription.KeyAlgorithm);
        Type type2 = key.GetType();
        if (type != type2 && !type.IsSubclassOf(type2) && !type2.IsSubclassOf(type))
            return false;

        HashAlgorithm hashAlgorithm = signatureDescription.CreateDigest();
        if (hashAlgorithm == null)
            throw new CryptographicException(SecurityResources.GetString("Cryptography_Xml_CreateHashAlgorithmFailed"));

        //Except this. The SignedXml class creates and cananicalizes a Signature element without any prefix, rather than using the element from the document provided
        byte[] c14NDigest = GetC14NDigest(signedXml, hashAlgorithm);

        AsymmetricSignatureDeformatter asymmetricSignatureDeformatter = signatureDescription.CreateDeformatter(key);
        return asymmetricSignatureDeformatter.VerifySignature(c14NDigest, signedXml.Signature.SignatureValue);
    }

    private static byte[] GetC14NDigest(SignedXml signedXml, HashAlgorithm hashAlgorithm)
    {
        Transform canonicalizeTransform = signedXml.SignedInfo.CanonicalizationMethodObject;
        XmlDocument xmlDoc = new XmlDocument();
        xmlDoc.LoadXml(signedXml.SignedInfo.GetXml().OuterXml);
        canonicalizeTransform.LoadInput(xmlDoc);
        return canonicalizeTransform.GetDigestedOutput(hashAlgorithm);
    }

    private static void AssignNameSpacePrefixToElementTree(XmlElement element, string prefix)
    {
        element.Prefix = prefix;

        foreach (var child in element.ChildNodes)
        {
            if (child is XmlElement)
                AssignNameSpacePrefixToElementTree(child as XmlElement, prefix);
        }
    }
}

Answer 3

显然很多人运行遇到了同样的问题。在调查了 class Signature 的源代码后，我得出的结论是 Microsoft 旨在帮助我们。 LoadXml() 方法中有硬编码前缀 "ds"。因此，可以生成签名，然后为其添加命名空间前缀 "ds"，加载修改后的签名并重新计算 "SignatureValue"。不幸的是，库中的错误使事情变得比他们需要的更难。下面是带有解决方法和注释的代码。

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;
    }

生成数字签名但具有特定的命名空间前缀 ("ds:")

Generate Digital Signature but with a Specific Namespace Prefix ("ds:")

c#

xml

digital-signature

prefixes