java RSA生成公钥和私钥

1.随机生成密钥对

 /**
     * 随机生成密钥对
     * @throws NoSuchAlgorithmException
     */
    public static void genKeyPair() throws NoSuchAlgorithmException {
        // KeyPairGenerator类用于生成公钥和私钥对，基于RSA算法生成对象
        KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance("RSA");
        // 初始化密钥对生成器，密钥大小为96-1024位
        keyPairGen.initialize(1024,new SecureRandom());
        // 生成一个密钥对，保存在keyPair中
        KeyPair keyPair = keyPairGen.generateKeyPair();
        // 得到私钥
        RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate();
        // 得到公钥
        RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();
        String publicKeyString = new String(Base64.encodeBase64(publicKey.getEncoded()));
        // 得到私钥字符串
        String privateKeyString = new String(Base64.encodeBase64((privateKey.getEncoded())));
        // 将公钥和私钥保存到Map
        //0表示公钥
        keyMap.put(0,publicKeyString);
        //1表示私钥
        keyMap.put(1,privateKeyString);
    }

2.RSA公钥加密

/**
     * RSA公钥加密
     * @param str 加密字符串
     * @param publicKey 公钥
     * @return 密文
     * @throws Exception 加密过程中的异常信息
     *
     */
    public static String encrypt( String str, String publicKey ) throws Exception{
        try {
            //base64编码的公钥
            byte[] decoded = Base64.decodeBase64(publicKey);
            RSAPublicKey pubKey = (RSAPublicKey) KeyFactory.getInstance("RSA").generatePublic(new X509EncodedKeySpec(decoded));
            //RSA加密
            Cipher cipher = Cipher.getInstance("RSA");
            cipher.init(Cipher.ENCRYPT_MODE, pubKey);
            byte[] strBytes = str.getBytes("UTF-8");
            int inputLength = strBytes.length;
            System.out.println("加密字节数：" + inputLength);
            // 最大加密字节数，超出最大字节数需要分组加密
            // 标识
            int offSet = 0;
            byte[] resultBytes = {};
            byte[] cache;
            while (inputLength - offSet > 0) {
                if (inputLength - offSet > MAX_ENCRYPT_BLOCK) {
                    cache = cipher.doFinal(strBytes, offSet, MAX_ENCRYPT_BLOCK);
                    offSet += MAX_ENCRYPT_BLOCK;
                } else {
                    cache = cipher.doFinal(strBytes, offSet, inputLength - offSet);
                    offSet = inputLength;
                }
                resultBytes = Arrays.copyOf(resultBytes, resultBytes.length + cache.length);
                System.arraycopy(cache, 0, resultBytes, resultBytes.length - cache.length, cache.length);
            }
            String outStr = Base64.encodeBase64String(resultBytes);
            return outStr;
        }catch (Exception e){
            System.out.println("rsaEncrypt error:" + e.getMessage());
        }
        return "";
    }

3.RSA私钥解密

 /**
     * RSA私钥解密
     * @param str 加密字符串
     * @param privateKey 私钥
     * @return 铭文
     * @throws Exception  解密过程中的异常信息
     */
    public static String decrypt(String str, String privateKey) throws Exception{
        //64位解码加密后的字符串
        byte[] inputByte = Base64.decodeBase64(str.getBytes("UTF-8"));
        //base64编码的私钥
        byte[] decoded = Base64.decodeBase64(privateKey);
        RSAPrivateKey priKey = (RSAPrivateKey) KeyFactory.getInstance("RSA").generatePrivate(new PKCS8EncodedKeySpec(decoded));
        //RSA解密
        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.DECRYPT_MODE, priKey);
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        int inputLen = inputByte.length;
        System.out.println("解密字节数：" + inputLen);
        int offset = 0;
        byte[] cache;
        int i = 0;
        // 对数据分段解密
        while (inputLen - offset > 0) {
            if (inputLen - offset > MAX_DECRYPT_BLOCK) {
                cache = cipher.doFinal(inputByte, offset, MAX_DECRYPT_BLOCK);
            } else {
                cache = cipher.doFinal(inputByte, offset, inputLen - offset);
            }
            out.write(cache, 0, cache.length);
            i++;
            offset = i * MAX_DECRYPT_BLOCK;
        }
        byte[] decryptedData = out.toByteArray();
        out.close();
        // 解密后的内容
        String outStr = new String(decryptedData);
        return outStr;
    }

4.使用

   private static final Map<Integer,String> keyMap=new HashMap<>();

    /**
     * RSA最大加密明文大小
     */
    private static final int MAX_ENCRYPT_BLOCK = 117;

    /**
     * RSA最大解密密文大小
     */
    private static final int MAX_DECRYPT_BLOCK = 128;

　　/**
     * @param args
     * @throws Exception
     */
    public static void main(String[] args) throws Exception {
        //生成公钥和私钥
        genKeyPair();
        //加密字符串
        String message = "sdaw";
        System.out.println("随机生成的公钥为:" + keyMap.get(0));
        System.out.println("随机生成的私钥为:" + keyMap.get(1));
        String messageEn = encrypt(message,keyMap.get(0));
        System.out.println(message + "\t加密后的字符串为:" + messageEn);
        String messageDe = decrypt(messageEn,keyMap.get(1));
        System.out.println("还原后的字符串为:" + messageDe);
    }