The goal of this project was creation of DES (56 bits) implementation with usage of ATMEL 89LS8252 microcontroller on the base of the pervously developed ANSI C compatible code. Later this project was divided in to two sub projects:

The difference between them is only way to present data and organization of communication with user.
AT89S8252 microcontroller was the most suitable candidate for this project because of the certain reasons (big enough reprogrammable 8 K Flash Memory, SPI interface, 2 K EEPROM for storing keys and sensitive data, 256 Bytes On-chip RAM, 2 DPTRs; 3-Level Program Memory Lock. Speaking about SPI interface I would recommend to use very simple but good programmer from Telesystems . I created a driver for this SPI programmer in order to have possibility to work with it under WINDOWS NT, WINDOWS 2000. May be later it will be published as well.
Clear, it would be much better to use a specialized microcontroller which is optimized for execution of special bits operations, but it is not easy to obtain such devices from microcontroller's vendors.
I will not spend a lot of time, speaking in detail about the project - I believe, you already have a certain experience with programming this type of microcontrollers. The understanding of DES subroutines will not be a big problem for you, there are all necessary comments. In order to help you to check crypto operations' results, I included in each project file "validate.txt" with pre-calculated results of crypto operations with pre-defined plain texts and keys.

• Firs subproject (mixed code (C and Assembler) was created for compatible with uVision2 (Keil) Integrated Development Environment. This project can be debugged in an interactive mode - you can interact with AT89S8252 simulator without leaving uVision2. In "Serial Window #1" you see menu, giving you possibility to encrypt, decrypt constant and user defined data, manipulate with ports IO lines. This is an excellent possibility to test this project without necessity to have and use any external hardware (hardware in circuit emulator), without additional efforts for creating device prototype. This project manages two keys: SUB key and TRANSPORT key. The difference between them is only nominal - they can be stored and used independently, but they share the same data buffer (there plain data are and there encrypted (decrypted) data will be put.
• Second subproject (pure assembler) is limited edition of the first one, created for M51 ( (Macro Assembler © 1992, Sergey Linev, excellent tool). I am sure it will be compiled with any modern macro assembler. This code is the most suitable code to be used with real applications, because it does not contain any auxiliary subroutines and allows working with one key. This project was tested with a test application (screenshot, I used DELPHI). Application used standard DES implementation and has sent plain data and keys to the microcontroller via serial port (RS232). Microcontroller executed required operation (encrypt-decrypt) and sent the result back the test application. Application compared the obtained result with its own and reported about errors. A lot of iterations were done in such way. Therefore, I really believe, that this code is workable.There is a possibility to check this implementation statically, without communication between test application and real microcontroller. In order to do it, you have to change M_LOAD_KEY and M_LOAD_DATA macros. I tested it with predefined values, taken from validate.txt (screenshot of M51 with "Internal Memory" window opened, encrypt operation was executed).

After downloading source codes, please read accompanied descriptions, it will help you a lot.

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