使用xml-crypto v4.0.1签名SAML XML时摘要值不匹配问题

环境信息 #

• xml-crypto版本：^4.0.1
• Node.js版本：v16.14.0

错误现象 #

签名SAML XML时出现验证错误：

invalid signature: for uri calculated digest is 2U1suBt1sOA2olbnbMK1gC/3FHk= but the xml to validate supplies digest OGXcEIgUP1W+Hv9ghexl8gdMtrI=

生成的签名后XML #

<samlp:Response xmlns:samlp="urn:oasis:names:tc:SAML:1.0:protocol">
    <saml:Assertion MajorVersion="1" MinorVersion="1"
        AssertionID="_1" Issuer="mydomain.com"
        IssueInstant="2023-08-13T03:01:27.265Z" xmlns:saml="urn:oasis:names:tc:SAML:1.0:assertion"
        Id="_0">
        <saml:Conditions NotBefore="2023-08-13T03:01:27.266Z"
            NotOnOrAfter="2023-08-14T03:01:27.263Z" />
        <saml:AuthenticationStatement AuthenticationMethod="urn:oasis:names:tc:SAML:1.0:am:password"
            AuthenticationInstant="2023-08-13T03:01:27.268Z">
            <saml:Subject>
                <saml:NameIdentifier Format="urn:oasis:names:tc:SAML:1.1:nameid-format:unspecified"
                    NameQualifier="urn:mydomain.com">123356</saml:NameIdentifier>
                <saml:SubjectConfirmation>
                    <saml:ConfirmationMethod>urn:oasis:names:tc:SAML:1.0:cm:bearer</saml:ConfirmationMethod>
                </saml:SubjectConfirmation>
            </saml:Subject>
        </saml:AuthenticationStatement>
        <saml:AttributeStatement>
            <saml:Subject>
                <saml:NameIdentifier Format="urn:oasis:names:tc:SAML:1.1:nameid-format:unspecified"
                    NameQualifier="urn:mydomain.com">123356</saml:NameIdentifier>
                <saml:SubjectConfirmation>
                    <saml:ConfirmationMethod>urn:oasis:names:tc:SAML:1.0:cm:bearer</saml:ConfirmationMethod>
                </saml:SubjectConfirmation>
            </saml:Subject>
            <saml:Attribute AttributeName="version" AttributeNamespace="mydomain.com">
                <saml:AttributeValue>1</saml:AttributeValue>
            </saml:Attribute>
        </saml:AttributeStatement>
    </saml:Assertion>
    <samlp:Status>
        <samlp:StatusCode Value="samlp:Success" />
    </samlp:Status>
    <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="#_0">
                <Transforms>
                    <Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature" />
                </Transforms>
                <DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1" />
                <DigestValue>OGXcEIgUP1W+Hv9ghexl8gdMtrI=</DigestValue>
            </Reference>
        </SignedInfo>
        <SignatureValue>
            HKJ/iE4XpJlwQW9H0zP8yK6SZO/HazYl/YpE09GTwDFcsgPRots+nosEeVtVU0wLkYW6wNgwf79LEoTiEComatyuRhVWg3ZtZpsdSkrkfR74M2B9aECoPS8k5tqArQbJl0KO...[redacted]...tsRlIJX9nMtdg==
        </SignatureValue>
    </Signature>
</samlp:Response>

当前使用的工具函数 #

去除XML空格函数 #

function removeXMLSpaces(string){
  let xmlString = string;
  xmlString = xmlString.replace(/>\s*/g, ">");
  xmlString = xmlString.replace(/\s*</g, "<");
  xmlString = xmlString.replace(/\r\n?/g, "\n");
  xmlString = xmlString.replace(/(\r\n\t|\n|\r\t)/gm, "");
  return xmlString;
}

XML签名函数 #

function signXml(xml, options) {
  console.log({ options });

  const sig = new SignedXml(options);

  // sig.keyInfoProvider = new KeyProvider();

  sig.signatureAlgorithm = "http://www.w3.org/2000/09/xmldsig#rsa-sha1";

  sig.canonicalizationAlgorithm = "http://www.w3.org/TR/2001/REC-xml-c14n-20010315";

  sig.addReference({
    xpath: "//*[local-name(.)='Assertion']",
    transforms: ["http://www.w3.org/2000/09/xmldsig#enveloped-signature"]
  });

  sig.computeSignature(xml);

  fs.writeFileSync(process.cwd() + "/xml/signed.xml", sig.getSignedXml());

  let currentSignedXML = sig.getSignedXml();
  currentSignedXML = currentSignedXML.replace("Id=\"_0\"","").replace("URI=\"#_0\"","URI=\"\"");

  return currentSignedXML;
}

问题根源与解决方案 #

核心问题 #

1. 签名后手动修改XML：签名完成后移除Id="_0"并清空URI的操作，直接破坏了签名的完整性。xml-crypto计算摘要时基于的是包含Id="_0"的Assertion节点，验证方计算时会用修改后的节点，自然和原签名的摘要值不匹配。
2. 自定义空格处理干扰规范化：removeXMLSpaces函数手动修改XML空格，会和xml-crypto自带的c14n规范化算法产生冲突，导致签名和验证时的源内容不一致。

修复步骤 #

1. 删除签名后的手动修改代码
   直接返回xml-crypto生成的原始签名XML，不要做任何字符串替换：

   function signXml(xml, options) {
     console.log({ options });
   
     const sig = new SignedXml(options);
   
     sig.signatureAlgorithm = "http://www.w3.org/2000/09/xmldsig#rsa-sha1";
     sig.canonicalizationAlgorithm = "http://www.w3.org/TR/2001/REC-xml-c14n-20010315";
   
     sig.addReference({
       xpath: "//*[local-name(.)='Assertion']",
       transforms: ["http://www.w3.org/2000/09/xmldsig#enveloped-signature"]
     });
   
     sig.computeSignature(xml);
   
     const signedXml = sig.getSignedXml();
     fs.writeFileSync(process.cwd() + "/xml/signed.xml", signedXml);
   
     return signedXml;
   }
   

2. 移除手动空格处理
   删掉removeXMLSpaces函数的调用，让xml-crypto通过指定的c14n算法自动处理XML格式，确保签名和验证时的规范化结果一致。

3. 按需配置Reference参数
   如果确实需要空URI或无Id的Assertion，要在签名前就调整好：

   • 若需要空URI：在addReference时直接设置uri: ""
   • 若不需要Assertion的Id：在传入signXml函数前就移除该属性

验证方法 #

修复后用以下代码测试签名有效性：

const fs = require('fs');
const { SignedXml, FileKeyInfo } = require('xml-crypto');

function verifyXml(xml, publicKeyPath) {
  const sig = new SignedXml();
  sig.keyInfoProvider = new FileKeyInfo(publicKeyPath);
  sig.loadSignature(xml);
  const isValid = sig.checkSignature(xml);
  if (!isValid) {
    console.error(sig.validationErrors);
  }
  return isValid;
}

const signedXml = fs.readFileSync(process.cwd() + "/xml/signed.xml", 'utf8');
console.log("验证结果:", verifyXml(signedXml, "path/to/public.key"));

内容的提问来源于stack exchange，提问作者IsekaM