iTextSharp 中的 Pade LTV 验证抛出公钥不是用于根 CA 证书的证书签名

Question

我得到一个Org.BouncyCastle.Security.InvalidKeyException错误消息公钥呈现不证书签名验证用PDF时LtvVerifier。

在绕过 CRL LDAP URI 的问题后出现了此问题。用于执行验证的代码与上一篇文章相同：

   public static bool Validate(byte[] pdfIn, X509Certificate2 cert)
    {
        using (var reader = new PdfReader(pdfIn))
        {
            var fields = reader.AcroFields;
            var signames = fields.GetSignatureNames();

            if (!signames.Any(n => fields.SignatureCoversWholeDocument(n)))
                throw new Exception("None signature covers all document");

            var verifications = signames.Select(n => fields.VerifySignature(n));

            var invalidSignature = verifications.Where(v => !v.Verify());
            var invalidTimeStamp = verifications.Where(v => !v.VerifyTimestampImprint());

            if (invalidSignature.Any())
                throw new Exception("Invalid signature found");
        }

        using (var reader = new PdfReader(pdfIn))
        {
            var ltvVerifier = new LtvVerifier(reader)
            {
                OnlineCheckingAllowed = false,
                CertificateOption = LtvVerification.CertificateOption.WHOLE_CHAIN,
                Certificates = GetChain(cert).ToList(),
                VerifyRootCertificate = false,
                Verifier = new MyVerifier(null)
            };

            var ltvResult = new List<VerificationOK> { };
            ltvVerifier.Verify(ltvResult);

            if (!ltvResult.Any())
                throw new Exception("Ltv verification failed");
        }
        return true;
   }

从证书链构建 X509Certificates 列表的辅助函数：

    private static X509.X509Certificate[] GetChain(X509Certificate2 myCert)
    {
        var x509Chain = new X509Chain();
        x509Chain.Build(myCert);

        var chain = new List<X509.X509Certificate>();
        foreach(var cert in x509Chain.ChainElements)
        {
            chain.Add(
                DotNetUtilities.FromX509Certificate(cert.Certificate)
                );
        }

        return chain.ToArray();
    }

自定义验证器，刚刚从示例中复制：

 class MyVerifier : CertificateVerifier
{
    public MyVerifier(CertificateVerifier verifier) : base(verifier) { }

    override public List<VerificationOK> Verify(
        X509.X509Certificate signCert, X509.X509Certificate issuerCert, DateTime signDate)
    {
        Console.WriteLine(signCert.SubjectDN + ": ALL VERIFICATIONS DONE");
        return new List<VerificationOK>();
    }
}

我已经重新实施LtvVerifier并CrlVerifier如上一个问题中所述。CRL 验证完成。

证书链包括用于签署 PDF 的证书和 CA 根证书。该函数CrlVerifier.Verify在调用下一行时抛出上述异常：

 if (verifier != null)
                result.AddRange(verifier.Verify(signCert, issuerCert, signDate));
            // verify using the previous verifier in the chain (if any)
            return result;

这是相关的堆栈跟踪Org.BouncyCastle.Security.InvalidKeyException：

   in Org.BouncyCastle.X509.X509Certificate.CheckSignature(AsymmetricKeyParameter publicKey, ISigner signature)
   in Org.BouncyCastle.X509.X509Certificate.Verify(AsymmetricKeyParameter key)
   in iTextSharp.text.pdf.security.CertificateVerifier.Verify(X509Certificate signCert, X509Certificate issuerCert, DateTime signDate)
   in iTextSharp.text.pdf.security.RootStoreVerifier.Verify(X509Certificate signCert, X509Certificate issuerCert, DateTime signDate)
   in PdfCommon.CrlVerifierSkippingLdap.Verify(X509Certificate signCert, X509Certificate issuerCert, DateTime signDate) in c:\Projects\digit\Fuentes\PdfCommon\CrlVerifierSkippingLdap.cs:line 76
   in iTextSharp.text.pdf.security.OcspVerifier.Verify(X509Certificate signCert, X509Certificate issuerCert, DateTime signDate)
   in PdfCommon.LtvVerifierSkippingLdap.Verify(X509Certificate signCert, X509Certificate issuerCert, DateTime sigDate) in c:\Projects\digit\Fuentes\PdfCommon\LtvVerifierSkippingLdap.cs:line 221
   in PdfCommon.LtvVerifierSkippingLdap.VerifySignature() in c:\Projects\digit\Fuentes\PdfCommon\LtvVerifierSkippingLdap.cs:line 148
   in PdfCommon.LtvVerifierSkippingLdap.Verify(List`1 result) in c:\Projects\digit\Fuentes\PdfCommon\LtvVerifierSkippingLdap.cs:line 112

以及指向我尝试验证的 pdf的链接

Answer 1

经过一番调试后发现

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当验证证书链不以自签名证书结尾时， iText(Sharp) 5.5.10LtvVerifier以观察到的方式失败。

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原因

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原因非常简单：LtvVerifier建立一系列Verifier实例（OcspVerifier、CrlVerifier、RootStoreVerifier、CertificateVerifier；最后一个通过基类调用链接）。然后，它请求相关签名的签名证书的证书链，并为链中的每个证书调用Verifier由该证书及其颁发者组成的证书对的序列；如果是链中的最终证书，null则作为颁发者证书转发。

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Verifier不幸的是，最后的CertificateVerifier, 假定在null颁发者证书的情况下要验证的证书是自签名的：

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// Check if the signature is valid\nif (issuerCert != null) {\n    signCert.Verify(issuerCert.GetPublicKey());\n}\n// Also in case, the certificate is self-signed\nelse {\n    signCert.Verify(signCert.GetPublicKey());\n} \n

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（来自CertificateVerifier方法Verify）

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如果最初请求的证书链LtvVerifier未以自签名证书结尾，则最终测试会正确地得出观察到的结果

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Org.BouncyCastle.Security.InvalidKeyException带有错误消息提供的公钥不适用于证书签名

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OP 的例子

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在当前的情况下，我们有一个由以下人员发布的文档时间戳

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cn=AUTORIDAD DE SELLADO DE TIEMPO FNMT-RCM, ou=CERES, o=FNMT-RCM, c=ES

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由...发出

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cn=AC Administraci\xc3\xb3n P\xc3\xbablica，序列号=Q2826004J，ou=CERES，o=FNMT-RCM，c=ES

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由...发出

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ou=AC RAIZ FNMT-RCM，o=FNMT-RCM，c=ES

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这是自签名的。

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在这种情况下，中间证书AC Administraci\xc3\xb3n P\xc3\xbablica已位于欧洲受信任列表中（参见西班牙的 TL 管理器，“信任服务提供商”，“F\xc3\xa1brica Nacional de Moneda”） y 音色 - Real Casa de la Moneda (FNMT-RCM)”、“信任服务”、“Certificados reconocidos para su uso en el \xc3\xa1mbito de...”、“数字身份”）。

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因此，不需要前两个以上的证书来建立信任，也不需要自签名根证书。因此，只有前两个证书嵌入时间戳中并作为证书链返回到LtvVerifier，而不是自签名根。

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结果是观察到的误差LtvVerifier。

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该怎么办？

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好吧，由于我们已经开始创建上一个问题中涉及的类的自己的副本，因此对它们进行更多更改应该是一种选择。

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在这种情况下，还应该更改RootStoreVerifier. 它的Verify方法如下所示：

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override public List<VerificationOK> Verify(X509Certificate signCert, X509Certificate issuerCert, DateTime signDate) {\n    LOGGER.Info("Root store verification: " + signCert.SubjectDN);\n    // verify using the CertificateVerifier if root store is missing\n    if (certificates == null)\n        return base.Verify(signCert, issuerCert, signDate);\n    try {\n        List<VerificationOK> result = new List<VerificationOK>();\n        // loop over the trusted anchors in the root store\n        foreach (X509Certificate anchor in certificates) {\n            try {\n                signCert.Verify(anchor.GetPublicKey());\n                LOGGER.Info("Certificate verified against root store");\n                result.Add(new VerificationOK(signCert, this, "Certificate verified against root store."));\n                result.AddRange(base.Verify(signCert, issuerCert, signDate));\n                return result;\n            } catch (GeneralSecurityException) {}\n        }\n        result.AddRange(base.Verify(signCert, issuerCert, signDate));\n        return result;\n    } catch (GeneralSecurityException) {\n        return base.Verify(signCert, issuerCert, signDate);\n    }\n}\n

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我们只需要删除标记线

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                signCert.Verify(anchor.GetPublicKey());\n                LOGGER.Info("Certificate verified against root store");\n                result.Add(new VerificationOK(signCert, this, "Certificate verified against root store."));\n                // vvv remove\n                result.AddRange(base.Verify(signCert, issuerCert, signDate));\n                // ^^^ remove\n                return result;\n

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在内try块中。由于我们刚刚确定证书signCert是由信任锚签名的，因此无论如何都不需要base.Verify。

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