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I am using an ESP-01 this way: MCU <-> UART <-> ESP-01, using AT firmware/NonOS on ESP-01.

I have my own encryption functions, and I would like to implement them both on MCU and ESP-01 sides at least for data packets, like those packets where ESP-01 send a data packet to the MCU starting with "+IPD" string, and also for the data that is sent from the MCU to the the ESP-01 after the MCU have sent the command AT+CIPSEND=n, being 'n' the quantity of data bytes to be sent.

Will I be able to to such modification on ESP-01 side? I mean, edit the NonOS "at"firmware? As I was looking, there is only few source files and much .a lib files in the folder of the SDK.

I want to do such encryption because my data is circulating unprotected between the ESP and the MCU. In my application, I use a SSL/TLS connection as internet client with the ESP with Google's Firebase database, but this way anyone could sniff my data by monitoring the UART signal. And to say, I am not able to use SSL/TLS (like mbedtls) inside the MCU because the MCU has limited flash memory size.

I already donwloaded the "ESP8266_NONOS_SDK-2.2.1", compiled it with virtual machine and did the download of the generated bins to the ESP-01, my question here is about the possibility to customize the "at" firmware.

Any suggestion for this case?

Regards, Jeferson.

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    \$\begingroup\$ What are you asking? In bold you say "about the possibility"...of course it is possible! Write your own AT handlers in C if you want. Are you asking for someone to give you the source files? What do you actually want? \$\endgroup\$ – Elliot Alderson Mar 7 at 15:23
  • \$\begingroup\$ I wanted to know if the source code (of at firmware) is available to make editions. \$\endgroup\$ – abomin3v3l Mar 7 at 16:44
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Why don't you just do everything on the ESP? There's no reason to use the AT interface and add a second microcontroller.

Having said that, I wonder how information gets into your MCU in a way that doesn't make it accessible to an adversary.

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  • \$\begingroup\$ The MCU has 100 pins and have so much signals connected to it, something that an ESP-01 would not afford. I did not understood your second statement. \$\endgroup\$ – abomin3v3l Mar 7 at 13:34
  • \$\begingroup\$ The ESP-01 is only a way the MCU can have access to internet, to databases. \$\endgroup\$ – abomin3v3l Mar 7 at 13:44
  • \$\begingroup\$ The data that comes into and out of the MCU are raw strings, I want to introduce a data shuffle for both sides, ESP and MCU. \$\endgroup\$ – abomin3v3l Mar 7 at 13:48
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    \$\begingroup\$ Aren't these raw strings available to sniffing, just like the UART lines? I guess I can not imagine what kind of attack you are worried about, if data shuffling is enough to make it safe. \$\endgroup\$ – Elliot Alderson Mar 7 at 14:28
  • \$\begingroup\$ Because the API secret key of the database (and other sensitive data) are sent through the serial lines (actually fom the MCU to the ESP-01), and I just want to shuffle such data packets, and if I do that I will need to do on both sides, the MCU side is ok for me, but I am asking about the ESP-01 side, and my current idea was to customize the at firmware of it (BUT, is that possible? I want to have this answer, and if the answer is YES, how to proceed). \$\endgroup\$ – abomin3v3l Mar 7 at 14:45

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