ECC有关DER文件的解析（Java）

ECC有关DER文件的解析（Java）

本篇博客提供有关ECC的DER文件的Java解析方式，如ECC公钥和ECC签名值对应DER文件的解析，PEM文件也能够使用本博客中提供的解析方式进行解析，PEM文件只是DER文件经过Base64编码之后，加上了头尾说明信息的一类文件而已。

ECC 公钥DER文件的解析

1. ECC公钥DER文件的数据结构层次
   
   2 解析

import org.bouncycastle.asn1.*;

import java.io.ByteArrayInputStream;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.spec.ECGenParameterSpec;

public class DecodeDERECCPubKey {
    public static void main(String[] args) throws Exception {
        Security.addProvider(new BouncyCastleProvider());
        byte[] derByte = getECCPubKey();
        ASN1Primitive asn1 = toAsn1Primitive(derByte);

        if(asn1 instanceof ASN1Sequence)
        {
            ASN1Sequence asn1Sequence = (ASN1Sequence) asn1;
            ASN1Encodable[] asn1Encodables = asn1Sequence.toArray();
            for (ASN1Encodable asn1Encodable : asn1Encodables) {
                ASN1Primitive asn1Primitive = asn1Encodable.toASN1Primitive();
                if(asn1Primitive instanceof DLSequence)
                {
                    DLSequence asn1DLSequence = (DLSequence) asn1Primitive;
                    ASN1Encodable[] asn1DLEncodables = asn1DLSequence.toArray();
                    for(ASN1Encodable asn1DLEncodable : asn1DLEncodables)
                    {
                        if(asn1DLEncodable instanceof ASN1ObjectIdentifier)
                        {
                            ASN1ObjectIdentifier asn1ObjectIdentifier = (ASN1ObjectIdentifier) asn1DLEncodable;
                            System.out.println(asn1ObjectIdentifier.toString());
                        }
                    }
                }
                else if(asn1Primitive instanceof DERBitString)
                {
                    DERBitString derBitString = (DERBitString) asn1Primitive;
                    System.out.println(derBitString.toString());
                }
            }
        }
    }

    private static ASN1Primitive toAsn1Primitive(byte[] data) throws Exception
    {
        try (ByteArrayInputStream inStream = new ByteArrayInputStream(data);
             ASN1InputStream asnInputStream = new ASN1InputStream(inStream);)
        {
            return asnInputStream.readObject();
        }
    }

    private static byte[] getECCPubKey() throws Exception {
        KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("ECDSA");
        ECGenParameterSpec ecParameterSpec = new ECGenParameterSpec("P-256");
        keyPairGenerator.initialize(ecParameterSpec);
        KeyPair keyPair = keyPairGenerator.generateKeyPair();

        return keyPair.getPublic().getEncoded();
    }
}
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ECC签名值DER文件的解析

1. ECC签名值DER文件的数据结构层次
   
2. 解析
   参考连接：DER Decode ECDSA Signature in Java
   源码复制

import java.io.ByteArrayInputStream;
import java.math.BigInteger;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.Security;
import java.security.Signature;
import java.security.spec.ECGenParameterSpec;

import org.bouncycastle.asn1.ASN1Encodable;
import org.bouncycastle.asn1.ASN1InputStream;
import org.bouncycastle.asn1.ASN1Integer;
import org.bouncycastle.asn1.ASN1Primitive;
import org.bouncycastle.asn1.ASN1Sequence;
import org.bouncycastle.jce.provider.BouncyCastleProvider;

public class DecodeEcdsaSignature {

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

        byte[] signature = getSignature();      
        ASN1Primitive asn1 = toAsn1Primitive(signature);

        if (asn1 instanceof ASN1Sequence) {
            ASN1Sequence asn1Sequence = (ASN1Sequence) asn1;
            ASN1Encodable[] asn1Encodables = asn1Sequence.toArray();
            for (ASN1Encodable asn1Encodable : asn1Encodables) {
                ASN1Primitive asn1Primitive = asn1Encodable.toASN1Primitive();
                if (asn1Primitive instanceof ASN1Integer) {
                    ASN1Integer asn1Integer = (ASN1Integer) asn1Primitive;
                    BigInteger integer = asn1Integer.getValue();
                    System.out.println(integer.toString());
                }
            }
        }

    }

    private static ASN1Primitive toAsn1Primitive(byte[] data) throws Exception
    {
        try (ByteArrayInputStream inStream = new ByteArrayInputStream(data);
                ASN1InputStream asnInputStream = new ASN1InputStream(inStream);) 
        {
            return asnInputStream.readObject();
        }
    }

    private static byte[] getSignature() throws Exception {
        KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("ECDSA");
        ECGenParameterSpec ecParameterSpec = new ECGenParameterSpec("P-256");
        keyPairGenerator.initialize(ecParameterSpec);
        KeyPair keyPair = keyPairGenerator.generateKeyPair();

        Signature signature = Signature.getInstance("SHA256withECDSA");
        signature.initSign(keyPair.getPrivate());
        signature.update("message to sign".getBytes("UTF-8"));

        return signature.sign();
    }
}
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有关DER文件的解析核心在于找到对应文件的数据结构层次信息。