openssl 操作RSA公私钥

//生成1024长度私钥
openssl genrsa -out key.pem 1024
//根据私钥生成公钥,公钥比较短，它只包括了数字n 和 常数 e
openssl rsa -in key.pem -pubout -out pubkey.pem
//公钥对文件进行加密
openssl rsautl -encrypt -in file1.txt -inkey pubkey.pem -pubin -out file2.txt
xxd file2.txt
//私钥解密
openssl rsautl -decrypt -in file2.txt -inkey key.pem

RSA加解密相关API

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最常用的是 PKICSIPADDING

有生成和导入没有就使用生成

导入公钥一般用 X509EncodeKeySpec方式

私钥一般使用PKCS8EncodeKeySpec方式导入

导入之后交给 keyFactory 才可以转化为 pubKey 和 privKey

package com.deepway.cryptology.rsa;

import cn.hutool.core.io.FileUtil;
import org.apache.commons.lang3.StringUtils;

import javax.crypto.Cipher;
import javax.crypto.NoSuchPaddingException;
import java.io.File;
import java.security.*;
import java.security.spec.EncodedKeySpec;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;

/**
 * RSA源码 RSAKeyPairGenerator
 *
 * @author huyanbing
 * @create 2022/12/19 12:27 上午
 */
public class RsaCipher {


    //sun.security.rsa.RSAPadding.padV15
    String algo = "RSA/ECB/PKCS1Padding";
    int keyLen = 1024;
    KeyPair keyPair;


    /**
     * 生成密钥对
     *
     * @return
     */
    public KeyPair generateKeyPair() throws NoSuchAlgorithmException {
        String algo = StringUtils.substringBefore(this.algo, "/");
        KeyPairGenerator generator = KeyPairGenerator.getInstance(algo);

        //1024,2048。。。
        generator.initialize(keyLen);
        KeyPair pair = generator.generateKeyPair();

        System.out.println("generateKeyPair:");
        System.out.println(pair);
        return pair;
    }


    /**
     * 导入密钥
     *
     * @return
     */
    public KeyPair importKeyPair() throws Exception {

        KeyFactory keyFactory = KeyFactory.getInstance("RSA");

        byte[] pub = FileUtil.readBytes(new File("pub.key"));
        EncodedKeySpec publicKeySpec = new X509EncodedKeySpec(pub);
        PublicKey pubKey = keyFactory.generatePublic(publicKeySpec);

        byte[] priv = FileUtil.readBytes(new File("priv.key"));
        //私钥用的是PKCS8EncodedKeySpec
        EncodedKeySpec privKeySpec = new PKCS8EncodedKeySpec(priv);
        PrivateKey privateKey = keyFactory.generatePrivate(privKeySpec);

        System.out.println("importKeyPair");

        System.out.println(pubKey);
        System.out.println(privateKey);

        return new KeyPair(pubKey, privateKey);

    }


    /**
     * 导出密钥到文件
     */
    public void exportKey() {
        FileUtil.writeBytes(keyPair.getPublic().getEncoded(), new File("pub.key"));
        FileUtil.writeBytes(keyPair.getPrivate().getEncoded(), new File("priv.key"));
    }


    /**
     * 加密方法
     *
     * @param plainText
     * @return
     */
    public byte[] encrypt(byte[] plainText) throws GeneralSecurityException {
        Cipher cipher = Cipher.getInstance(algo);
        //使用加密模式  公钥
        cipher.init(Cipher.ENCRYPT_MODE, keyPair.getPublic());
        return cipher.doFinal(plainText);
    }

    /**
     * 解密方法
     *
     * @param cipherText
     * @return
     * @throws GeneralSecurityException
     */
    public byte[] decrypt(byte[] cipherText) throws GeneralSecurityException {
        Cipher cipher = Cipher.getInstance(algo);
        //使用解密模式 私钥
        cipher.init(Cipher.DECRYPT_MODE, keyPair.getPrivate());

        return cipher.doFinal(cipherText);

    }


    public static void main(String[] args) throws Exception {


        RsaCipher bob = new RsaCipher();

        //bob.keyPair = bob.importKeyPair();

        bob.keyPair = bob.generateKeyPair();
        bob.exportKey();

        //Alice:
        RsaCipher alice = new RsaCipher();
        alice.keyPair = new KeyPair(bob.keyPair.getPublic(), null);

        byte[] y = alice.encrypt("Deepway  is  no 1".getBytes());

        //Bob:
        byte[] x = bob.decrypt(y);

        //解密为
        System.out.println(new String(x));

    }
}

源码解读 RSAKeyPairGenerator

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计算 phi=（p-1）*(q-1)

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e 和 phi的最大公约数是1

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确保 e 和 phi 是互质的

计算私钥d 是e 关于phi_n的模反元素

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优化rsa

            // private exponent d is the inverse of e mod phi
            BigInteger d = e.modInverse(phi);

            // 性能优化 提前计算
            // 1st prime exponent pe = d mod (p - 1)
            BigInteger pe = d.mod(p1);
            // 2nd prime exponent qe = d mod (q - 1)
            BigInteger qe = d.mod(q1);

            // crt coefficient coeff is the inverse of q mod p
            BigInteger coeff = q.modInverse(p);