如何验证数字签名的XML文件？

Question

嗨，我很新的数字签名。我正在验证数字签名的XML文件，我已经验证它使用下面的代码。但我想知道它是如何验证XML是否正确或被篡改。在阅读一些文章后，我发现 1.为XML创建散列（不包括签名部分） 2.使用公钥解密签名（您将获得散列值） 3.比较两个散列。 （如果两个哈希匹配，那么XML没有被篡改）。 我的理解是对的？

这是我的XML

<Signature xmlns="http://www.w3.org/2000/09/xmldsig#"> 
    <SignedInfo> 
     <CanonicalizationMethod Algorithm="http://www.w3.org/TR/2001/REC-xml-c14n-20010315" /> 
     <SignatureMethod Algorithm="http://www.w3.org/2000/09/xmldsig#rsa-sha1" /> 
     <Reference URI=""> 
     <Transforms> 
      <Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature" /> 
     </Transforms> 
     <DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1" /> 
     <DigestValue>u+1NVN5c3gbaxmIrkO9SzVQDklA=</DigestValue> 
     </Reference> 
    </SignedInfo> 
    <SignatureValue>QtQJjevrggzsFZj7PqD3p7GaWkzJAfyacjbMgMXgszCuO+Pxe2rrkScqvgGt2DJqgVlTbC/m9gnodCu7BcXSmW459mSJtyGH+ekWwj6g9ej8I7IYWCRqbI5uus3r3+vr/8ECd5CP/khu/LcCMyPuNIxA8h2EywCeQgbXBvLiWcdexBazdKQQpFxlKw0i+oTs8Ou6jViOdX1ZmTRtdKCQXzAElvpyNimQSmO9OECEs/TytjzIG98mpldfdofoq/2JC+xQhs6IF+Ctw/zlJdkgj1U18U/00Cw4puT4oScTELNSihSS+i9gAL+YjZLlIeunACbnZ4B1CVL/uS9kLlutXQ==</SignatureValue> 
    <KeyInfo> 
     <KeyValue> 
     <RSAKeyValue> 
      <Modulus>kHORMZQYOifL5UdIhKe54SfvJKyzLL5Aaw9MgpzeQPgBMmD9KMRnkeU+5RYMiUW8GT3q4eW77UihyxSX3MTAHzuqXoc6GjkBO1Tr41isud721SG7iMspw829YZKAHAPDAl0BV5gpLZagH8KXrDp4dVU+XDOOLZZZWZnbpKSFKvLaJO34KphZ/9W3L/l1BOwEs7132svmtwGgPO2Y16C90sDRWp78ZCYYhb7fAez7683+fijZCDGuVTvS0lBKhmH0ETiNfBAiELUUwHvQ5GHOFSp5PA8+hV9F7zxno1a0/OBpRsHfLydm3THyMUS7DlPE46zPiO9rRIUe90aQ64ulYQ==</Modulus> 
      <Exponent>AQAB</Exponent> 
     </RSAKeyValue> 
     </KeyValue> 
    </KeyInfo> 
    </Signature> 

和签名部分的我​​是多么验证XML：

private void btnVerifySign_Click(object sender, EventArgs e) 
     { 
string LModulus = node.SelectSingleNode("//Signature/KeyInfo/KeyValue/RSAKeyValue/Modulus").InnerText.ToString(); 
       string LExponent = node.SelectSingleNode("//Signature/KeyInfo/KeyValue/RSAKeyValue/Exponent").InnerText.ToString(); 
using (var rsa = new RSACryptoServiceProvider()) 
       { 
var rsaParam = new RSAParameters() 
        { 
Modulus = Convert.FromBase64String(LModulus), 
         Exponent = Convert.FromBase64String(LExponent) 
        }; 
rsa.ImportParameters(rsaParam); 
bool result = VerifyXml(newxml1, rsa); 
} 

public static Boolean VerifyXml(XmlDocument Doc, RSA Key) 
     { 
      // Check arguments. 
      if (Doc == null) 
       throw new ArgumentException("Doc"); 
      if (Key == null) 
       throw new ArgumentException("Key"); 

      // Create a new SignedXml object and pass it 
      // the XML document class. 
      SignedXml signedXml = new SignedXml(Doc); 

      // Find the "Signature" node and create a new 
      // XmlNodeList object. 
      XmlNodeList nodeList = Doc.GetElementsByTagName("Signature"); 

      // Throw an exception if no signature was found. 
      if (nodeList.Count <= 0) 
      { 
       // throw new CryptographicException("Verification failed: No Signature was found in the document."); 
       MessageBox.Show("Verification failed: No Signature was found in the document."); 
      } 

      // This example only supports one signature for 
      // the entire XML document. Throw an exception 
      // if more than one signature was found. 
      if (nodeList.Count > 1) 
      { 
       MessageBox.Show("Verification failed: More that one signature was found for the document."); 
       // throw new CryptographicException("Verification failed: More that one signature was found for the document."); 
      } 

      // Load the first <signature> node. 
      signedXml.LoadXml((XmlElement)nodeList[0]); 

      // Check the signature and return the result. 
      return signedXml.CheckSignature(Key); 
     } 

这儿如果我修改XML并验证它通过VerifyXml方法返回false和如果我不修改xml VerifyXml方法返回true。我想知道它是如何验证XML的？我尝试过比较nodeList [0]中被篡改和未被篡改的XML的值，并且得到了相同的值，但是签署了XML.CheckSignature（Key）返回true/false。对于不同的xml，摘要值应该不同？在这里，我获得了修改和未修改的xml的相同摘要值。并基于CheckSignature（Key）返回true/false。何时为XML创建哈希值？谢谢。

Answer 1

其实它是<SignedInfo>有符号的元素，而不是数据对象。数据对象的散列值包含在<SignedInfo>元素的<Reference>元素中。因此数据对象也是间接签名的。验证签名时，将数据对象的散列值与<Reference>元素中的数据的有符号摘要进行比较。然后使用公钥检查<SignedInfo>元素上的签名。

欲了解更多信息，你可以阅读RFC 3275。您可以在这里找到有关签名xml的生成和验证步骤的信息。