simple rsa demo

SimpleRSA.java

package org.jiacheo.awesome.blockchain.encrypt.communication;

import java.math.BigInteger;
import java.util.Random;

/**
 * Created on 2022/8/22. <br/> contact: <a style="color:yellow;text-decoration:none;"
 * href="mailto:jiacheo@qipeng.com" target="_blank">jiacheo[at]qipeng.com</a> <br/>
 *
 * @author jiacheo
 */
public class SimpleRSA {

  public static void main(String[] args) {
    BigInteger ONE = new BigInteger("1");
    BigInteger TWO = new BigInteger("2");

    //random p、q，created for generate n、d、e，than drop them。
    BigInteger p = new BigInteger(128, 128, new Random());
    BigInteger q = new BigInteger(128, 128, new Random());
    BigInteger n = q.multiply(p);
    BigInteger upperLimit = n.subtract(ONE);

    //选择从1到n-1之间的一个随机数，且该随机数不能是偶数。否则BigInteger.modInverse 会抛异常
    BigInteger d;
    Random random = new Random();
    do {
      d = new BigInteger(upperLimit.bitLength(), random);
    }
    while (d.compareTo(upperLimit) >= 0 || d.compareTo(ONE) <= 0 || d.mod(TWO).compareTo(ONE) < 0);
    System.out.println("p=0x" + p.toString(16));
    System.out.println("q=0x" + q.toString(16));
    System.out.println("n=0x" + n.toString(16));
    System.out.println("d=0x" + d.toString(16));

    BigInteger modulo = p.subtract(ONE).multiply(q.subtract(ONE));
    System.out.println("m=0x"+modulo.toString(16));
    BigInteger e = d.modInverse(modulo);
    System.out.println("e=0x" + e.toString(16));

    //source data
    BigInteger sourceMessage = BigInteger.probablePrime(128, random);
    System.out.println("sourceMessage=" + sourceMessage.toString(36));

    //encrypt， e/n pair is public key
    BigInteger data = sourceMessage.modPow(e, n);
    System.out.println("encryptedData=0x" + data.toString(16));

    //decrypt, d/n pair is private key
    BigInteger decryptedData = data.modPow(d, n);
    System.out.println("decryptedData=" + decryptedData.toString(36));

    //compare equivalent
    System.out.println("equals?="+sourceMessage.equals(decryptedData));
  }
}

One of a test result:

p=0x9be0ce1aa99bfe790115c75ef7366ded
q=0xf81209704a01bc04825b8e5f8fed71e9
n=0x970cc33798d8310e2721390e1fcbbf37cf8a7de4c16722619440e64c2e78a9b5
d=0x3a458c16a2f923ee26923caefbaf78f471b4fffb9feda9fec125307a682404b3
m=0x970cc33798d8310e2721390e1fcbbf363b97a659cdc967e410cf908da754c9e0
e=0x4bdbc60fa89806c2e585ad783ed2ede5db06546b4858add2f7bc6d58216d739b
sourceMessage=89i8uoap0izgf4f9w9hg6jvvn
encryptedData=0x75d9a3c8ce8698cef4ae7e63cd40122b74f4dbea4068d6626585cf81c8d430b3
decryptedData=89i8uoap0izgf4f9w9hg6jvvn
equals?=true

come from the paper （author by Christian Reitwießner）, the theory shows as below screent shots: