Calculate Bootbase/bootext secret for debug commands (ATEN 1,xxxx) - Zyxel, Huawei, ZTE, etc. - similar to zynpass but working for larger devices

zynsecrets.c

/* 
Calculate Bootbase/bootext secret for debug commands 
Zyxel, Huawei, ZTE, etc.

Usage:
$ gcc zynsecrets.c -o zynsecrets
$ ./zynsecrets 000102030403

Copyright (C) Kost, https://gist.github.com/kost

*/

#include <stdio.h>
#include <stdlib.h> /* for exit() */
#include <stdint.h> /* uint types */
#include <limits.h> /* for CHAR_BIT */
#include <string.h> 

/* https://en.wikipedia.org/wiki/Circular_shift#Implementing_circular_shifts */
uint32_t rotr32 (uint32_t value, unsigned int count) {
    const unsigned int mask = (CHAR_BIT*sizeof(value)-1);
    count &= mask;
    return (value>>count) | (value<<( (-count) & mask ));
}

/* Zyn secret generation */
uint32_t calc_secret(uint32_t seed, uint8_t mac, uint32_t magic) {
      uint32_t b = seed & 0x00FFFFFF;
      uint32_t r = rotr32(b + magic, mac & 7);
      return r^b;
}

void givehelp (char *prg) {
	printf("%s: <seed> [mac] [magic]\n",prg);
	printf("Example: %s 010203040506\n",prg);
	printf("Example: %s 010203040506 AB\n",prg);
	printf("Example: %s 010203040506 AB A11F5AC6\n",prg);
	exit(1);
}

int main (int argc, char *argv[]) {
	char *fullseed=NULL;
	uint32_t res;
	uint32_t mac=0;
	uint32_t seed=0;
	uint32_t magic=0;

	char seedch[7], macch[3];

	int i;

	if (argc<2) {
		givehelp(argv[0]);
	} else {
		if (strcmp(argv[1],"--help")==0 || strcmp(argv[1],"-h")==0) {
			givehelp(argv[0]);
		}
		fullseed=argv[1];
		strncpy (seedch, argv[1], 6);
		seed=strtol(seedch, NULL, 16);
		strncpy (macch, fullseed + strlen(fullseed) - 2, 2);
		mac=strtol(macch, NULL, 16);
		magic=0x10F0A563;
	}
	if (argc>2) {
		sscanf(argv[2],"%X",&mac);
		magic=0xA11F5AC6;
	}
	if (argc>3) {
		sscanf(argv[3],"%X",&magic);
	}
	fprintf(stderr,"Args: ");
	for (i=1; i< argc; i++) {
		fprintf(stderr,"%s ",argv[i]);
	}
	fprintf(stderr,"\n");

	fprintf (stderr,"Seed: %08X\n", seed);
	fprintf (stderr,"Mac: %08X\n", mac);
	fprintf (stderr,"Magic: %08X\n", magic);
	fprintf (stderr,"\n");

	res = calc_secret(seed,mac,magic);
	printf("%X\n", res);
}