android平台 AES256加密使用

1 加密流程

     客户端底层私有数据，如用户信息，服务器信息等数据需要在保存时加密，使用时解密，具体流程为使用公钥进行加密，使用私钥进行解密。此密钥对置于客户端，不宜与服务端通讯秘钥一致。

    客户端与服务端进行通讯数据加密，此时私钥不宜置于客户端，整体流程为客户端使用公钥对请求数据进行加密，服务端使用私钥进行解密，响应客户端时使用私钥进行加密，客户端得到数据使用私钥进行解密。

2 秘钥保存

  直接放置于java端是不太安全的，可放置于native层，或者使用其他加密处理。

3 具体代码实现：

        private static final int MAX_ENCRYPT_BLOCK = 117;  
	private static final int MAX_DECRYPT_BLOCK = 128; 
	
	/*分段加解密实现*/
	public static byte[] decryptByPrivateKey(PrivateKey privateKey, byte[] encryptedData) throws Exception {
        Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
        cipher.init(Cipher.DECRYPT_MODE, privateKey);
        int inputLen = encryptedData.length;
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        int offSet = 0;

        for(int i = 0; inputLen - offSet > 0; offSet = i * MAX_DECRYPT_BLOCK) {
            byte[] cache;
            if(inputLen - offSet > MAX_DECRYPT_BLOCK) {
                cache = cipher.doFinal(encryptedData, offSet, MAX_DECRYPT_BLOCK);
            } else {
                cache = cipher.doFinal(encryptedData, offSet, inputLen - offSet);
            }

            out.write(cache, 0, cache.length);
            ++i;
        }

        byte[] decryptedData = out.toByteArray();
        out.close();
        return decryptedData;
    }
    
	public static byte[] decryptByPublicKey(PublicKey publicKey, byte[] encryptedData) throws Exception {
        Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
        cipher.init(Cipher.DECRYPT_MODE, publicKey);
        int inputLen = encryptedData.length;
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        int offSet = 0;

        for(int i = 0; inputLen - offSet > 0; offSet = i * MAX_DECRYPT_BLOCK) {
            byte[] cache;
            if(inputLen - offSet > MAX_DECRYPT_BLOCK) {
                cache = cipher.doFinal(encryptedData, offSet, MAX_DECRYPT_BLOCK);
            } else {
                cache = cipher.doFinal(encryptedData, offSet, inputLen - offSet);
            }

            out.write(cache, 0, cache.length);
            ++i;
        }

        byte[] decryptedData = out.toByteArray();
        out.close();
        return decryptedData;
    }
    
	
    public static byte[] encryptByPublicKey(PublicKey publicKey, byte[] data) throws Exception {
        Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
        cipher.init(Cipher.ENCRYPT_MODE, publicKey);
        int inputLen = data.length;
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        int offSet = 0;

        for(int i = 0; inputLen - offSet > 0; offSet = i * MAX_ENCRYPT_BLOCK) {
            byte[] cache;
            if(inputLen - offSet > MAX_ENCRYPT_BLOCK) {
                cache = cipher.doFinal(data, offSet, MAX_ENCRYPT_BLOCK);
            } else {
                cache = cipher.doFinal(data, offSet, inputLen - offSet);
            }

            out.write(cache, 0, cache.length);
            ++i;
        }

        byte[] encryptedData = out.toByteArray();
        out.close();
        return encryptedData;
    }