java - 使用充气城堡从证书中提取 keyUsage 扩展

Question

我正在编写一个小型 CA 实现。可以从现有证书引导此 CA。执行此操作后，我想验证输入是否具有正确的扩展名:

private static final Set<String> REQUIRED_CA_EXTENSIONS = Set.of(
        Extension.keyUsage.getId(),
        Extension.subjectKeyIdentifier.getId());

private static void validateExtensions(final X509Certificate certificate) {
    if (!CertificateExtensions.getAll(certificate).containsAll(REQUIRED_CA_EXTENSIONS)) {
        throw new RuntimeException("Attempted to create a CA from a certificate without required extensions");
    }
}

// Util method
public static Set<String> getAll(final X509Certificate certificate) {
    final Set<String> extensions = new HashSet<>();
    extensions.addAll(certificate.getCriticalExtensionOIDs());
    extensions.addAll(certificate.getNonCriticalExtensionOIDs());
    return extensions;
}

但是，这仅验证扩展是否存在。我还需要验证 keyUsage 扩展是否包含 keyCertSign 和 cRLSign 才能签署证书。

如何使用充气城堡和/或 JCA 来做到这一点？

Answer 1

JCA 上有一个可用的方法 X509Certificate返回 keyUsage 扩展的位，简单地称为 getKeyUsage() 。根据 Java 文档，键用法的各个位由返回数组中的 boolean 值表示。

还可以使用 BouncycaSTLe 库做更多的工作来实现相同的结果。我展示了这两种方法，因为 BouncycaSTLe 库为检查 X509Certificate 提供了更完整的支持，因此如果您想做更困难的事情，有一个示例来说明简单的事情很有用。

请注意，截至撰写本文时，这需要两个 BouncycaSTLe 库，即主提供程序/加密库以及 PKIX/CMS 库。

import org.bouncycastle.asn1.ASN1Primitive;
import org.bouncycastle.asn1.x509.KeyUsage;
import org.bouncycastle.cert.X509CertificateHolder;

import java.io.FileInputStream;
import java.security.cert.CertificateFactory;
import java.security.cert.X509Certificate;

public class X509CheckKeyUsage {

    public static void main(String[] args) throws Exception {
        FileInputStream fis = new FileInputStream("DST_X3_CA.pem"); // for example
        CertificateFactory cf = CertificateFactory.getInstance("X.509");
        X509Certificate cert = (X509Certificate) cf.generateCertificate(fis);

        // check with simple JCA methods

        boolean [] keyUsageBools = cert.getKeyUsage();
        final int KEY_CERT_SIGN = 5;
        final int CRL_SIGN = 6;
        boolean usagesVerified = keyUsageBools[KEY_CERT_SIGN] && keyUsageBools[CRL_SIGN];
        System.out.println("key usage bits verified? " + usagesVerified);

        // Convert the jca x.509 cert to a bouncycastle x.509 cert, in two steps

        org.bouncycastle.asn1.x509.Certificate bcCert = org.bouncycastle.asn1.x509.Certificate
                .getInstance(ASN1Primitive.fromByteArray(cert.getEncoded())); // step 1
        X509CertificateHolder bcX509Cert = new X509CertificateHolder(bcCert); // step 2

        // now verify keyUsage bits

        final int requiredKeyUsageBits = KeyUsage.keyCertSign | KeyUsage.cRLSign;
        usagesVerified = KeyUsage.fromExtensions(bcX509Cert.getExtensions()).hasUsages(requiredKeyUsageBits);
        System.out.println("key usage bits verified? " + usagesVerified);
    }
}