使用Bouncy Castle（pom版本：bcprov-jdk15on 1.59）中SM2算法进行解析证书、验签

以下都没有做异常处理，只是简单抛出，如果抽取成工具类，使用时应仔细处理

SM2 解析数字证书

public  void subject()
{  
    String demo = "证书";    
    byte[] decode = Base64.getDecoder().decode(demo);    
    getCert(decode);
}
public static void getCert(byte[] buf){    
    ByteArrayInputStream bIn;    
    ASN1InputStream aIn;    
    bIn = new ByteArrayInputStream(buf);    
    aIn = new ASN1InputStream(bIn);    
    try {      
        ASN1Sequence seq = (ASN1Sequence) aIn.readObject(); 
        X509CertificateStructure cert = new X509CertificateStructure(seq);
        System.out.println("****************************");
        System.out.println("证书版本:\t"+cert.getVersion()); 
        System.out.println("序列号:\t\t"+cert.getSerialNumber().getValue().toString(16));    
        System.out.println("算法标识:\t"+cert.getSignatureAlgorithm().getAlgorithm());        
        System.out.println("签发者:\t\t"+cert.getIssuer());        //GMT 格林威治标准时间         	
        System.out.println("开始时间:\t"+cert.getStartDate().getTime());       
        System.out.println("结束时间:\t"+cert.getEndDate().getTime());        
        System.out.println("主体名:\t\t"+cert.getSubject()); 
        System.out.print("签名值:\t");        
        DERBitString signature=cert.getSignature();        
        String strSign=new String(Hex.encode(signature.getBytes()));        
        System.out.println(strSign);        
        System.out.println("主体公钥:\t");        
        SubjectPublicKeyInfo pukinfo=cert.getSubjectPublicKeyInfo();        
        System.out.println("\t标识符:\t"+pukinfo.getAlgorithmId().getAlgorithm());
        byte[] byPuk=pukinfo.getPublicKeyData().getBytes();
        String strPuk=new String(Hex.encode(byPuk));
        System.out.println("\t公钥值:\t"+strPuk);        
        System.out.println("****************************");
              } catch (IOException e) {
              e.printStackTrace();  
        }
    }



=======================================================
### SM2 验签

 在实际应用的时候，签名实际上并不是针对原始消息，而是针对原始消息的哈希进行签名 ，对签名进行验证实际上就是用公钥解密，然后把解密后的哈希与原始消息的哈希进行对比。因为用户总是使用自己的私钥进行签名，所以，私钥就相当于用户身份。而公钥用来给外部验证用户身份。

```java
  public static void main(String[] args) throws CertificateException, InvalidKeyException, NoSuchAlgorithmException, SignatureException, UnsupportedEncodingException {

        String certStr = "证书";
        String plaintext = "原文";
        String temp = "签名值";
    
        byte[] signValue = Base64.decode(temp);
        CertificateFactory factory = new CertificateFactory();
        X509Certificate certificate = (X509Certificate) factory.engineGenerateCertificate(
        new ByteArrayInputStream(Base64.decode(certStr)));
        System.out.println(certificate.getSigAlgName());
        Signature signature = Signature.getInstance(certificate.getSigAlgName()
        ,new BouncyCastleProvider());
        signature.initVerify(certificate);
        signature.update(plaintext.getBytes("GBK"));
        System.out.println(signature.verify(signValue));
        /**
         *   打印原文不同格式的各种编码
         */
  System.out.println(Arrays.toString(plaintext.getBytes("GBK")));
        System.out.println(Arrays.toString(plaintext.getBytes("UTF8")));
        System.out.println(Arrays.toString(plaintext.getBytes(StandardCharsets.UTF_8)));
        System.out.println(Arrays.toString(plaintext.getBytes(StandardCharsets.ISO_8859_1)));
    }