--- title: "14-STM32+W5500 Basic Control (Self-built IoT Platform) - Porting mbedtls to enable STM32+W5500" url: "https://maker.wiznet.io/gavinchang/projects/14-stm32-w5500-basic-control-self-built-iot-platform-porting-mbedtls-to-enable-stm32-w5500/" markdown_url: "https://maker.wiznet.io/gavinchang/projects/14-stm32-w5500-basic-control-self-built-iot-platform-porting-mbedtls-to-enable-stm32-w5500/md" type: "UCC: User Created Content" author: "Yang Fengwu" author_url: "https://www.cnblogs.com/yangfengwu/p/15869618.html" editor: "WIZnet" editor_url: "https://maker.wiznet.io/" original_author: "Yang Fengwu" original_url: "https://www.cnblogs.com/yangfengwu/p/15869618.html" published: "2025-12-04" language: "en" likes: 0 views: 468 comments: 0 source: "WIZnet Makers (https://maker.wiznet.io/)" --- # 14-STM32+W5500 Basic Control (Self-built IoT Platform) - Porting mbedtls to enable STM32+W5500 > 14-STM32+W5500 Basic Control (Self-built IoT Platform) - Porting mbedtls to enable STM32+W5500 to connect to an MQTT server using SSL one-way authentication (wi Original author: Yang Fengwu (source: https://www.cnblogs.com/yangfengwu/p/15869618.html) ## Article ## **illustrate** ### **In network communication, without SSL, information is exposed in plaintext.** ### **This section demonstrates how to port the mbedtls library to enable the W5500 to connect to the MQTT server using SSL.** ### **First, let me briefly explain SSL. Essentially, it's all about TCP communication with the server.** ### **However, after establishing a TCP connection with the server, the encryption method and password must first be negotiated with the server.** ### **The data is then transmitted in encrypted form.** ## **test** ### **1. Open the code in this section.illustrate** ### **In network communication, without SSL, information is exposed in plaintext.** ### **This section demonstrates how to port the mbedtls library to enable the W5500 to connect to the MQTT server using SSL.** ### **First, let me briefly explain SSL. Essentially, it's all about TCP communication with the server.** ### **However, after establishing a TCP connection with the server, the encryption method and password must first be negotiated with the server.** ### **The data is then transmitted in encrypted form.** ## **test** ### **1. Open the code in this section.** ![](https://maker.wiznet.io/upload/ckeditor5/1066384665%5F1764847359%2Epng) ### **2. Modify to your own Alibaba Cloud device information** ![](https://maker.wiznet.io/upload/ckeditor5/1066384665%5F1764847379%2Epng) ### **3. Download to the microcontroller (connect via network cable)** ![](https://maker.wiznet.io/upload/ckeditor5/1066384665%5F1764847398%2Epng) ### **4. Observe the log printing port to confirm that the server is connected.** ![](https://maker.wiznet.io/upload/ckeditor5/1066384665%5F1764847434%2Epng)、 ![](https://maker.wiznet.io/upload/ckeditor5/1066384665%5F1764847450%2Epng) ## **Program Description** ### **1. To facilitate the use of mbedtls' SSL functionality, I have encapsulated it as follows.** ![](https://maker.wiznet.io/upload/ckeditor5/1066384665%5F1764847479%2Epng) ### **2. First, let me mention a few functions that I need to implement, as mbedtls will call these functions at the underlying level.** #### **Random number function and timestamp return function (not needed if certificate time is not verified).** ![](https://maker.wiznet.io/upload/ckeditor5/1066384665%5F1764847501%2Epng) **Network receive processing function (mbedtls automatically calls this function at its underlying level)** The underlying way SSL retrieves data is by specifying how much data is needed, and then returning that amount of data. So after I receive the data, I store it in a circular queue, and then I provide the SSL with as much data as needed. ![](https://maker.wiznet.io/upload/ckeditor5/1066384665%5F1764847525%2Epng) #### **Network sending function (mbedtls automatically calls this function at the underlying level)** ![](https://maker.wiznet.io/upload/ckeditor5/1066384665%5F1764847548%2Epng) **3. Functions for sending and retrieving data using SSL** #### **We could actually use these two functions directly, but I wrapped them in another function for easier calling.** #### **After the SSL negotiation is complete, the data we send needs to call the functions provided by mbedtls. ** #### **Internally, our data will be encrypted before being sent out via TCP; ** #### **Similarly, we also need to use the functions provided by mbedtls to retrieve the data received via TCP.** ![](https://maker.wiznet.io/upload/ckeditor5/1066384665%5F1764848046%2Epng) ### **4. SSL Initialization** #### **The last two functions, highlighted in red, are the TCP data sending and receiving functions we mentioned above.** ![](https://maker.wiznet.io/upload/ckeditor5/1066384665%5F1764848069%2Epng) ### **5. Wait for the SSL handshake to complete.** #### **This function needs to be called in a polling manner after our TCP connection is successfully established. It automatically implements SSL internally, and returns 0 once SSL is successfully implemented.** ![](https://maker.wiznet.io/upload/ckeditor5/1066384665%5F1764848091%2Epng) ## **Now let's look at the specific usage.** ### **1. After establishing a TCP connection, poll and wait for SSL to succeed.** ![](https://maker.wiznet.io/upload/ckeditor5/1066384665%5F1764848114%2Epng) ### **2. After successful connection, send the MQTT protocol connection request.** #### **Please note that Alibaba Cloud stipulates that if using an SSL connection, the securemode parameter of the MQTT client_id must be set to 2.** ![](https://maker.wiznet.io/upload/ckeditor5/1066384665%5F1764848135%2Epng) ![](https://maker.wiznet.io/upload/ckeditor5/1066384665%5F1764848148%2Epng) ### **3. Retrieving data from SSL** ![](https://maker.wiznet.io/upload/ckeditor5/1066384665%5F1764848168%2Epng) ### **4. Of course, the underlying MQTT data transmission mechanism was also changed to use SSL for transmission.** ![](https://maker.wiznet.io/upload/ckeditor5/1066384665%5F1764848186%2Epng) **Conclusion** ### **In reality, it's still TCP communication, only the plaintext data has been encrypted.** ### **After the TCP connection is established, the encryption method and password negotiated with the server are implemented internally by mbedtls.** ### **Once the agreement is reached, we can send and receive data normally, except that it goes through mbedtls' internal functions in the process;** --- Source: https://maker.wiznet.io/gavinchang/projects/14-stm32-w5500-basic-control-self-built-iot-platform-porting-mbedtls-to-enable-stm32-w5500/