java读取sm2证书

读取SM2证书需要使用Bouncy Castle库，以下是Java代码示例：

import org.bouncycastle.asn1.ASN1ObjectIdentifier;
import org.bouncycastle.asn1.x509.AlgorithmIdentifier;
import org.bouncycastle.asn1.x509.SubjectPublicKeyInfo;
import org.bouncycastle.cert.X509CertificateHolder;
import org.bouncycastle.cert.jcajce.JcaX509CertificateConverter;
import org.bouncycastle.jcajce.provider.asymmetric.ec.BCECPublicKey;
import org.bouncycastle.jce.provider.BouncyCastleProvider;
import org.bouncycastle.openssl.PEMParser;
import org.bouncycastle.openssl.jcajce.JcaPEMKeyConverter;
import org.bouncycastle.util.io.pem.PemObject;
import org.bouncycastle.util.io.pem.PemReader;

import java.io.FileReader;
import java.security.KeyFactory;
import java.security.Security;
import java.security.cert.CertificateFactory;
import java.security.cert.X509Certificate;
import java.security.interfaces.ECPublicKey;
import java.security.spec.ECNamedCurveParameterSpec;
import java.security.spec.ECPublicKeySpec;

public class SM2CertReader {

    public static void main(String[] args) throws Exception {
        Security.addProvider(new BouncyCastleProvider());

        // 读取证书
        CertificateFactory cf = CertificateFactory.getInstance("X.509", "BC");
        X509Certificate cert = (X509Certificate) cf.generateCertificate(new FileReader("sm2_cert.pem"));

        // 读取公钥
        SubjectPublicKeyInfo spki = SubjectPublicKeyInfo.getInstance(cert.getPublicKey().getEncoded());
        AlgorithmIdentifier algId = spki.getAlgorithm();
        ASN1ObjectIdentifier oid = algId.getAlgorithm();
        if (!oid.getId().equals("1.2.840.10045.2.1")) {
            throw new IllegalArgumentException("Expecting SM2 public key");
        }
        byte[] publicKeyBytes = spki.getPublicKeyData().getBytes();
        PemObject pemObject = new PemObject("PUBLIC KEY", publicKeyBytes);
        PemReader pemReader = new PemReader(new FileReader("sm2_pub_key.pem"));
        pemObject = pemReader.readPemObject();
        pemReader.close();
        publicKeyBytes = pemObject.getContent();
        JcaPEMKeyConverter converter = new JcaPEMKeyConverter().setProvider("BC");
        ECPublicKey publicKey = (ECPublicKey) converter.getPublicKey(spki);

        // 打印公钥参数
        ECNamedCurveParameterSpec spec = (ECNamedCurveParameterSpec) publicKey.getParams();
        System.out.println("Curve: " + spec.getName());
        System.out.println("X: " + publicKey.getW().getAffineX());
        System.out.println("Y: " + publicKey.getW().getAffineY());
    }
}

其中，`sm2_cert.pem`是SM2证书文件，`sm2_pub_key.pem`是SM2公钥文件。在读取公钥时，需要先解析SubjectPublicKeyInfo，再读取PEM格式的公钥文件，最后使用JcaPEMKeyConverter转换为ECPublicKey类型。打印公钥参数时，需要使用ECPublicKey的getParams()方法获取椭圆曲线参数。