Quote from james789 on March 21, 2024, 9:09 pm

Sending encrypted data between two Mega328s using the 128-bit PC1 encryption algorithm.
Based on the example of SimuleIDE 1.0.0: Mega328_usart which send a counter between two Mega328s.

The PC1 algorithm is available in many different languages , this allows the data to be sent to a computer as well.

http://pccipher.free.fr/pc1/index.html

The data is encrypted with a 128-bit key and then sent over the serial port one byte at a time and decrypted on the other Mega328.
One can view the encrypted data by opening the serial monitor.

PROGRAM:

The program (in Arduino C) uses a PC1.h header file.

/* SENDER */

/* Send encrypted counter from mega328 to mega328 */
/* To view encrypted data open Serial Monitor and Print: Value */
/* The key must be same at sender and recevier */

#include "pc1.h"

byte data;

void setup() 
{
    DDRB = 0xFF;
    PORTB = 0;
    Serial.begin(9600);
    data = 0;

    // 128-bit key //
    unsigned char crypt_key[16]={0xD4,0xB7,0xE3,0xE8,0x88,0x4C,0x3C,0x54,0x95,0x3F,0x71,0xAA,0x42,0x75,0xBA,0xD1};
		
	for (int i=0;i<16;i++) key[i]=crypt_key[i];
	initPc1();
}

void loop() 
{
	dataCrypt=data;
    cryptPc1(0); /* 0 = crypt 1 = decrypt */
    Serial.write( dataCrypt );
    PORTB = data;
    data++;

    delay( 500 ); 
}

/* RECEIVER */

/* Receive and decrypt counter from mega328 */
/* To view encrypted data open Serial Monitor and Print: Value */
/* The key must be same at sender and recevier */

#include "pc1.h"

volatile byte data;

void setup() 
{
    DDRB = 0xFF;
    PORTB = 0;
    Serial.begin(9600);
    data = 0;

	// 128-bit key //
    unsigned char crypt_key[16]={0xD4,0xB7,0xE3,0xE8,0x88,0x4C,0x3C,0x54,0x95,0x3F,0x71,0xAA,0x42,0x75,0xBA,0xD1};
		
	for (int i=0;i<16;i++) key[i]=crypt_key[i];
	initPc1();
}

void loop() 
{
    if( Serial.available() ) 
    {
        data = Serial.read();
		dataCrypt=data;
	    cryptPc1(1); /* 0 = crypt 1 = decrypt */
		data=dataCrypt;
        PORTB = data;
    }
}

/* PC1.H file */

   /* PC1 Encryption Cipher 128-bit key */

	unsigned int sum1 = 0;
    unsigned int sum2 = 0;
    unsigned int keyXorVal = 0;
    unsigned int j, curByte;
    unsigned short wkey[8];
    unsigned int i;
	unsigned char dataCrypt;
    unsigned char key[16];
   
 void initPc1()
{
	    for (i = 0; i < 8; i++) {
        wkey[i] = (key[i * 2] << 8) | key[i * 2 + 1];
    }
}
void cryptPc1(int decryption)
{
    	unsigned int temp1 = 0;
    	unsigned int byteXorVal = 0;
        for (j = 0; j < 8; j++) {
            temp1 ^= wkey[j];
            sum2 = (sum2 + j) * 20021 + sum1;
            sum1 = (temp1 * 346) & 0xFFFF;
            sum2 = (sum2 + sum1) & 0xFFFF;
            temp1 = (temp1 * 20021 + 1) & 0xFFFF;
            byteXorVal ^= temp1 ^ sum2;
        }
        curByte = dataCrypt;
 
          if (!decryption) {
	        keyXorVal = curByte * 257;
        }

        curByte = ((curByte ^ (byteXorVal >> 8)) ^ byteXorVal) & 0xFF;

		  if (decryption) {
            keyXorVal = curByte * 257;
        }

        for (j = 0; j < 8; j++) {
            wkey[j] ^= keyXorVal;
        }
        dataCrypt = curByte;
}