How to use PHP to implement Modbus TCP data encryption and decryption

How to use PHP to implement data encryption and decryption of Modbus TCP

Introduction:
Modbus TCP is a commonly used industrial communication protocol used to transmit data in industrial control systems. However, due to the open nature of communications, there may be data security risks. In order to protect the confidentiality of data, we can use encryption algorithms to encrypt and decrypt the data transmitted in Modbus TCP communication. This article will introduce how to use PHP language to implement the data encryption and decryption functions of Modbus TCP.

1. Introduction to Modbus TCP
Modbus TCP is an industrial communication protocol based on TCP/IP protocol. It allows different devices to communicate via Ethernet or the Internet, enabling data reading and writing operations. The data format of Modbus TCP communication is binary transmission using 16-bit register address identification, which includes function code, register address, data length and other information.

2. Principle of data encryption and decryption
In Modbus TCP communication, we can ensure the confidentiality of the data by encrypting the transmitted data. Commonly used encryption algorithms include symmetric encryption and asymmetric encryption.

1. Symmetric encryption
   The symmetric encryption algorithm uses the same key for encryption and decryption, and the encryption and decryption algorithms are reversible. Commonly used symmetric encryption algorithms include AES, DES, etc. In Modbus TCP communication, we can use symmetric encryption algorithms to encrypt and decrypt the transmitted data.
2. Asymmetric encryption
   The asymmetric encryption algorithm uses public keys and private keys for encryption and decryption. The encryption and decryption algorithms are irreversible. Commonly used asymmetric encryption algorithms include RSA, DSA, etc. In Modbus TCP communication, we can use asymmetric encryption algorithms to encrypt and decrypt the transmitted data.

3. Use PHP to implement data encryption and decryption
Before using PHP language to implement Modbus TCP data encryption and decryption, we need to install the Crypt_RSA library first. We can install it through Composer and use the following command:

composer require phpseclib/phpseclib

1. Symmetric encryption implementation
   The following is a sample code for using the AES algorithm to encrypt and decrypt Modbus TCP data:

   // 加密
   $key = '1234567890abcdef';
   $plaintext = 'Modbus TCP data to encrypt';
   
   $ciphertext = openssl_encrypt($plaintext, 'AES-128-CBC', $key, OPENSSL_RAW_DATA, '1234567890abcdef');
   $encryptedData = base64_encode($ciphertext);
   
   // 解密
   $deciphertext = base64_decode($encryptedData);
   $data = openssl_decrypt($deciphertext, 'AES-128-CBC', $key, OPENSSL_RAW_DATA, '1234567890abcdef');

2. Asymmetric encryption implementation
   The following is a sample code for encrypting and decrypting Modbus TCP data using the RSA algorithm:

   // 加密
   $publicKey = '-----BEGIN PUBLIC KEY-----
   MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDVl/xqRyLcHUyVzDm6vHVb+3Tb
   gJVnEwPHMD/L2D4IDRRh88/fN9uZF2yN4W3rl5vpDEyTQqyutWYS+jD7hr/R6h7o
   D7yYaowIxL7eYqzA4foPgIa1YXRWVY+0+KGuk3RB2tZm2yrLzYbXq7OeOgZMJW1g
   SW+x9Z79+Xeq4dHJswIDAQAB
   -----END PUBLIC KEY-----';
   
   $privateKey = '-----BEGIN RSA PRIVATE KEY-----
   MIICXQIBAAKBgQDVl/xqRyLcHUyVzDm6vHVb+3TbgJVnEwPHMD/L2D4IDRRh88/f
   N9uZF2yN4W3rl5vpDEyTQqyutWYS+jD7hr/R6h7oD7yYaowIxL7eYqzA4foPgIa1
   YXRWVY+0+KGuk3RB2tZm2yrLzYbXq7OeOgZMJW1gSW+x9Z79+Xeq4dHJswIDAQAB
   AoGBAJcCf/zFt3k26hERDq9cBmPM4C3Tae/QK6xGMWH3+weZyD9Y6THg3Xugwv6q
   3FxcJxxb0BZHyx3Yuet8DKWHTq+u30yWsHEIo6XF0vJ+yc4tRUP02BgAX7pfVi/Z
   tw6e3YCVczpBgFhFpWLUtSd+4ohUKVSrO68OUetHzhmbt0+BAkEA/kH8dcog/wZ+
   xrgLHD3NazbN8atZXnB3qvLlL+Ev8nL1izLq5KjVk5tr4DYVz9mYqYynrd2zIZfe
   mXvY5F6/NwJBAOzHnlyJDg1RlcJUbMBiYZpQfUm5w9Kej14C6dPn0+vunHZA5Uyl
   8L+HXPCHu8rIYPb4a6blPbbtKs+8pU8E0qUCQGY33hxijhMOQ+2xP+VopquY4l76
   PLVnoz/n4cA81FUsMRP5+N+XwxTKAuhbq823ReYK56d/iafU9cZzT4EPsvMCQQCj
   0s1LjNzhJiOMBClees5kNrRVEcUIYJ6SRTG0U3XK4SynlcD6kUVP3V5Xnnw8v6KY
   mXTAd5O6ladvONpbcSfDAkASfwoGSjKga3WDvWJS5PW4KjAUsJD210AEx2f2zovc
   fIEunQKoToRuSVz8+WfYa/oBuKNU3K1Df6JMaTe6Jojf
   -----END RSA PRIVATE KEY-----';
   
   $plaintext = 'Modbus TCP data to encrypt';
   
   $encryptedData = '';
   openssl_public_encrypt($plaintext, $encryptedData, $publicKey);
   
   // 解密
   $decryptedData = '';
   openssl_private_decrypt($encryptedData, $decryptedData, $privateKey);

Conclusion:
By using PHP language and symmetric encryption algorithm or asymmetric encryption algorithm, we can encrypt and decrypt the data transmitted in Modbus TCP communication, thereby improving the security and confidentiality of the data. In practical applications, appropriate encryption algorithms and keys can be selected according to needs to ensure the security of communication data.

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