RSA加密解密

1.自己写一个类RSAUtils把下面的代码添加进去

static class  RSAUtils{
        //这里的参数随便写
        private static final String PRIVATE_KEY ="1" ;
        private static final String PUBLIC_KEY ="2" ;

        /**
         * 计算出公钥私钥用map存储
         * @return
         * @throws Exception
         */
        public static Map genKeyPair() throws Exception {
            KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance("RSA");
            //这个值关系到块加密的大小，可以更改，但是不要太大，否则效率会低
            keyPairGen.initialize(1024);
            KeyPair keyPair = keyPairGen.generateKeyPair();
            RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();
            RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate();
            Map keyMap = new HashMap(2);
            keyMap.put(PUBLIC_KEY, publicKey);
            keyMap.put(PRIVATE_KEY, privateKey);
            return keyMap;
        }

        /**
         * 

         * 获取私钥
         * 
         *
         * @param keyMap 密钥对
         * @return
         * @throws Exception
         */
        public static Key getPrivateKey(Map keyMap)
        throws Exception {
            Key key = (Key) keyMap.get(PRIVATE_KEY);
            return key;
            // return Base64Utils.encode(key.getEncoded());
        }

        /**
         * 

         * 获取公钥
         * 
         *
         * @param keyMap 密钥对
         * @return
         * @throws Exception
         */
        public static Key getPublicKey(Map keyMap)
        throws Exception {
            Key key = (Key) keyMap.get(PUBLIC_KEY);
            return key;
            //return Base64Utils.encode(key.getEncoded());
        }



        /**
         * 加密
         *
         * @param key  加密的密钥
         * @param data 待加密的明文数据
         * @return 加密后的数据
         * @throws Exception
         */
        public byte[] encrypt(Key key, byte[] data) throws Exception {
            try {
                Cipher cipher = Cipher.getInstance("RSA");
                cipher.init(Cipher.ENCRYPT_MODE, key);
                //获得加密块大小，如:加密前数据为128个byte，而key_size=1024 加密块大小为127 byte,加密后为128个byte;
                //因此共有2个加密块，第一个127 byte第二个为1个byte
                int blockSize = cipher.getBlockSize();
                int outputSize = cipher.getOutputSize(data.length);//获得加密块加密后块大小
                int leavedSize = data.length % blockSize;
                int blocksSize = leavedSize != 0 ? data.length / blockSize + 1 : data.length / blockSize;
                byte[] raw = new byte[outputSize * blocksSize];
                int i = 0;
                while (data.length - i * blockSize > 0) {
                    if (data.length - i * blockSize > blockSize)
                        cipher.doFinal(data, i * blockSize, blockSize, raw, i * outputSize);
                    else
                        cipher.doFinal(data, i * blockSize, data.length - i * blockSize, raw, i * outputSize);
                    //这里面doUpdate方法不可用，查看源代码后发现每次doUpdate后并没有什么实际动作除了把byte[]放到ByteArrayOutputStream中
                    //，而最后doFinal的时候才将所有的byte[]进行加密，可是到了此时加密块大小很可能已经超出了OutputSize所以只好用dofinal方法。
                    i++;
                }
                return raw;
            } catch (Exception e) {
                throw new Exception(e.getMessage());
            }
        }


        /**
         * 解密
         *
         * @param key 解密的密钥
         * @param raw 已经加密的数据
         * @return 解密后的明文
         * @throws Exception
         */
        public byte[] decrypt(Key key, byte[] raw) throws Exception {
            try {
                Cipher cipher = Cipher.getInstance("RSA");
                cipher.init(cipher.DECRYPT_MODE, key);
                int blockSize = cipher.getBlockSize();
                ByteArrayOutputStream bout = new ByteArrayOutputStream(64);
                int j = 0;
                while (raw.length - j * blockSize > 0) {
                    bout.write(cipher.doFinal(raw, j * blockSize, blockSize));
                    j++;
                }
                return bout.toByteArray();
            } catch (Exception e) {
                throw new Exception(e.getMessage());
            }
        }

    }
}

2.自己在创建个类Base64Helper把下面的添加进去

import android.util.Base64;
public class Base64Helper {
	//base64编码原文是否是6的整数倍？末尾几个“=”号？	
	public static String encode(byte[] data) {
		return Base64.encodeToString(data, Base64.DEFAULT);
	}
	public static byte[] decode(String str) {
		return Base64.decode(str, Base64.DEFAULT);
	}
}

3.主布局

4.主函数

public class MainActivity extends AppCompatActivity {
    private TextView tv,tv2;
    private EditText ed;
    private Key publicKey,privateKey;
    private RSAUtils rsaUtils;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        tv= (TextView) findViewById(R.id.tv);
        tv2= (TextView) findViewById(R.id.tv2);
        ed= (EditText) findViewById(R.id.et);
        try {
            //解密用公钥    加密用私钥
            Map keyPair = RSAUtils.genKeyPair();
            //获取公钥
            publicKey = RSAUtils.getPublicKey(keyPair);
            //获取私钥
            privateKey = RSAUtils.getPrivateKey(keyPair);



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

    }

    public void cc(View view) throws Exception {
                  rsaUtils = new RSAUtils();//实例化工具类
        switch (view.getId()) {
            case R.id.but1:
                //加密
                String s = ed.getText().toString();
                byte[] bytes = s.getBytes();
                try {
               //第一个参数是获取得到的私钥    第二个参数是你想要加密的内容
                    byte[] encrypt = rsaUtils.encrypt(privateKey, bytes);
                    String encode = Base64Helper.encode(encrypt);
                    tv.setText(encode);

                } catch (Exception e) {
                    e.printStackTrace();
                }
                break;
            case R.id.but2:
                //解密
                String s1 = tv2.getText().toString();
                byte[] bytes1 = s1.getBytes();
                //第一个参数是获取得到的公钥    第二个参数是你想要解密的暗文
                byte[] decrypt = rsaUtils.decrypt(publicKey, bytes1);
                tv2.setText(new String(decrypt,0,decrypt.length));
                break;
        }
    }