使用java实现RSA [英] RSA implementation using java

问题描述

我在java中实现RSA我遇到了一个代码，下面给出的代码在解密明文后以数字形式显示明文，但我想用简单的英文输入它。我不想使用java api。

I am implementing RSA in java I have encountered a code which is given below it is showing plaintext in numeric form after decrypting the plaintext, but I want it in simple english which I entered. I don't want to use the java api.

TestRsa.Java

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

public class TestRsa {

    private BigInteger p, q;
    private BigInteger n;
    private BigInteger PhiN;
    private BigInteger e, d;

    public TestRsa() {
        initialize();
    }

    public void initialize() {
        int SIZE = 512;
        /* Step 1: Select two large prime numbers. Say p and q. */
        p = new BigInteger(SIZE, 15, new Random());
        q = new BigInteger(SIZE, 15, new Random());
        /* Step 2: Calculate n = p.q */
        n = p.multiply(q);
        /* Step 3: Calculate ø(n) = (p - 1).(q - 1) */
        PhiN = p.subtract(BigInteger.valueOf(1));
        PhiN = PhiN.multiply(q.subtract(BigInteger.valueOf(1)));
        /* Step 4: Find e such that gcd(e, ø(n)) = 1 ; 1 < e < ø(n) */
        do {
            e = new BigInteger(2 * SIZE, new Random());
        } while ((e.compareTo(PhiN) != 1)
                || (e.gcd(PhiN).compareTo(BigInteger.valueOf(1)) != 0));
        /* Step 5: Calculate d such that e.d = 1 (mod ø(n)) */
        d = e.modInverse(PhiN);
    }

    public BigInteger encrypt(BigInteger plaintext) {
        return plaintext.modPow(e, n);
    }

    public BigInteger decrypt(BigInteger ciphertext) {
        return ciphertext.modPow(d, n);
    }

    public static void main(String[] args) throws IOException {
        TestRsa app = new TestRsa();
        int plaintext;
        System.out.println("Enter any character : ");
        plaintext = System.in.read();
        BigInteger bplaintext, bciphertext;
        bplaintext = BigInteger.valueOf((long) plaintext);
        bciphertext = app.encrypt(bplaintext);
        System.out.println("Plaintext : " + bplaintext.toString());
        System.out.println("Ciphertext : " + bciphertext.toString());
        bplaintext = app.decrypt(bciphertext);
        System.out.println("After Decryption Plaintext : "
                + bplaintext.toString());
    }
}

推荐答案

我的RSA类：

package com.infovale.cripto;

import java.io.UnsupportedEncodingException;
import java.math.BigInteger;
import java.security.InvalidKeyException;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.NoSuchAlgorithmException;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.PKCS8EncodedKeySpec;
import java.util.Arrays;

import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;

public class RSA {


static String kPublic = "";
static String kPrivate = "";

public RSA()
{

}


public String Encrypt(String plain) throws NoSuchAlgorithmException,
        NoSuchPaddingException, InvalidKeyException,
        IllegalBlockSizeException, BadPaddingException {

    String encrypted;
    byte[] encryptedBytes;      

    KeyPairGenerator kpg = KeyPairGenerator.getInstance("RSA");
    kpg.initialize(1024);
    KeyPair kp = kpg.genKeyPair();

    PublicKey publicKey = kp.getPublic();
    PrivateKey privateKey = kp.getPrivate();

    byte[] publicKeyBytes = publicKey.getEncoded();
    byte[] privateKeyBytes = privateKey.getEncoded();

    kPublic = bytesToString(publicKeyBytes);
    kPrivate = bytesToString(privateKeyBytes);

    Cipher cipher = Cipher.getInstance("RSA");
    cipher.init(Cipher.ENCRYPT_MODE, publicKey);
    encryptedBytes = cipher.doFinal(plain.getBytes());

    encrypted = bytesToString(encryptedBytes);
    return encrypted;

}

public String Decrypt(String result) throws NoSuchAlgorithmException,
        NoSuchPaddingException, InvalidKeyException,
        IllegalBlockSizeException, BadPaddingException {

    byte[] decryptedBytes;

    byte[] byteKeyPrivate = stringToBytes(kPrivate);

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

    PrivateKey privateKey = null;
    try {

        privateKey = kf.generatePrivate(new PKCS8EncodedKeySpec(byteKeyPrivate));

    } catch (InvalidKeySpecException e) {
        e.printStackTrace();
    }

    String decrypted;

    Cipher cipher = Cipher.getInstance("RSA");
    cipher.init(Cipher.DECRYPT_MODE, privateKey);
    decryptedBytes = cipher.doFinal(stringToBytes(result));
    decrypted = new String(decryptedBytes);
    return decrypted;

}

public String bytesToString(byte[] b) {
    byte[] b2 = new byte[b.length + 1];
    b2[0] = 1;
    System.arraycopy(b, 0, b2, 1, b.length);
    return new BigInteger(b2).toString(36);
}

public byte[] stringToBytes(String s) {
    byte[] b2 = new BigInteger(s, 36).toByteArray();
    return Arrays.copyOfRange(b2, 1, b2.length);
}
}

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