在 iTextSharp 中 Pades LTV 验证抛出 Public 密钥不用于根 CA 证书的证书签名

Question

在使用 LtvVerifier 验证 pdf 时，我收到 Org.BouncyCastle.Security.InvalidKeyException 错误消息 Public key presented not for certificate signature。

这个问题是在之后出现的。用于执行验证的代码和前面一样post:

   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 X509 证书列表的辅助函数：

    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>();
    }
}

我已经按照上一个问题中的说明重新实现了 LtvVerifier 和 CrlVerifier。 CRL 验证完成。

证书链包括用于签署 PDF 的证书和 CA 根证书。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 Org.BouncyCastle.Security.InvalidKeyException 的相关堆栈跟踪：

   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

还有一个link to the pdf that I try to validate

Answer 1

调试后发现

iText(Sharp) 5.5.10 LtvVerifier 在验证证书链未以 self-signed 证书结尾的证书时，以观察到的方式失败。

原因

原因很简单：LtvVerifier 建立了 Verifier 个实例的序列（OcspVerifier、CrlVerifier、RootStoreVerifier、CertificateVerifier ; 最后一个通过 base class 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由该证书及其颁发者组成的证书对的 Verifier 序列；如果是链中的最终证书，null 将作为颁发者证书转发。

不幸的是，最终 Verifier，即 CertificateVerifier，假设 null 颁发者证书要验证的证书是 self-signed:

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

（来自CertificateVerifier方法Verify）

如果 LtvVerifier 最初请求的证书链没有以 self-signed 证书结尾，则最终测试正确地导致观察到的

Org.BouncyCastle.Security.InvalidKeyException with error message Public key presented not for certificate signature

OP 的例子

在手头的案例中，我们有

发布的文档时间戳

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

发布者

cn=AC Administración Pública, serialNumber=Q2826004J, ou=CERES, o=FNMT-RCM, c=ES

发布者

ou=AC RAIZ FNMT-RCM, o=FNMT-RCM, c=ES

即self-signed。

在这种情况下，中间证书 AC Administración Pública 已经在欧洲信任列表中（参见 the TL manager for Spain、"Trust Service Provider"、"Fábrica Nacional de Moneda y Timbre - Real Casa de la Moneda (FNMT-RCM)"、"Trust Service"、"Certificados reconocidos para su uso en el ámbito de... "、"Digital Identity").

因此，建立信任不需要超过前两个证书，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给 LtvVerifier，而不是自签名根。

结果是 LtvVerifier 中观察到的错误。

怎么办？

好吧，由于我们已经开始在中创建我们自己的相关 classes 副本，因此可以选择对它们进行更多更改。

在这种情况下，应该另外更改 RootStoreVerifier。它的 Verify 方法如下所示：

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

我们只需要删除标记的行

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

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

在 iTextSharp 中 Pades LTV 验证抛出 Public 密钥不用于根 CA 证书的证书签名

Pades LTV verification in iTextSharp throws Public key presented not for certificate signature for root CA certificate

c#

pdf

itext

digital-signature

原因

OP 的例子

怎么办？