main.c

#include "schnorr.h"

#include <inttypes.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>

int main(int argc, char **argv) {
    int rounds = 10;
    if (argc > 1) {
        char *end_ptr = NULL;
        long parsed = strtol(argv[1], &end_ptr, 10);
        if (end_ptr == argv[1] || *end_ptr != '\0' || parsed <= 0 || parsed > 10000) {
            fprintf(stderr, "Usage: %s [rounds]\n", argv[0]);
            return EXIT_FAILURE;
        }
        rounds = (int)parsed;
    }

    SchnorrParams params;
    if (!schnorr_generate_safe_prime_params(&params)) {
        fprintf(stderr, "Failed to generate Schnorr parameters.\n");
        return EXIT_FAILURE;
    }

    SchnorrKeyPair keys;
    schnorr_keygen(&params, &keys);

    printf("Schnorr ZKP demo (interactive sigma protocol)\n");
    printf("p=%" PRIu64 ", q=%" PRIu64 ", g=%" PRIu64 "\n", params.p, params.q, params.g);
    printf("Public key y=g^x mod p: %" PRIu64 "\n", keys.public_y);
    printf("Running %d proof rounds...\n\n", rounds);

    for (int i = 0; i < rounds; i++) {
        SchnorrProof proof;
        schnorr_prove(&params, &keys, &proof);

        int accepted = schnorr_verify(&params, keys.public_y, &proof);
        printf("Round %d: c=%" PRIu64 ", accepted=%s\n", i + 1, proof.challenge_c, accepted ? "true" : "false");

        if (!accepted) {
            printf("Verification failed in an honest-proof round.\n");
            return EXIT_FAILURE;
        }

        if (i == rounds - 1) {
            SchnorrProof tampered = proof;
            tampered.response_s = schnorr_add_mod(tampered.response_s, 1ULL, params.q);
            int tampered_ok = schnorr_verify(&params, keys.public_y, &tampered);
            printf("Tamper test (modified response) accepted=%s\n", tampered_ok ? "true" : "false");
            if (tampered_ok) {
                printf("Unexpected tamper acceptance.\n");
                return EXIT_FAILURE;
            }
        }
    }

    printf("\nAll rounds accepted with real witness, tampered proof rejected.\n");
    return EXIT_SUCCESS;
}