secp256k1_tests.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <secp256k1.h>

int main() {
    secp256k1_context* ctx;
    secp256k1_pubkey pubkey;
    const unsigned char *seckey = (unsigned  char*) "Secret Key Br0!";

    ctx = secp256k1_context_create(SECP256K1_CONTEXT_SIGN | SECP256K1_CONTEXT_VERIFY);

    if (!secp256k1_ec_pubkey_create(ctx, &pubkey, seckey)) {
        printf("Failed to create pubkey\n");
        return 1;
    }

    size_t size = 33 * sizeof(char);
    unsigned char *out = (unsigned char *)malloc(size);
    char *hex = (char *)malloc(size * 2);

    secp256k1_ec_pubkey_serialize(ctx, out, &size, &pubkey, SECP256K1_EC_COMPRESSED);

    for (int i = 0, j = 0; i < strlen((const char*)out); ++i, j += 2) {
        sprintf(hex + j, "%02x", out[i] & 0xff);
    }

    printf("Public key: %s\n", hex);

    secp256k1_ecdsa_signature sig;
    const unsigned char *msg = (unsigned char*)"This is the message";

    if (!secp256k1_ecdsa_sign(ctx, &sig, msg, seckey, NULL, NULL)) {
        printf("Unable to sign the message\n");
        return 1;
    }

    size_t sig_len = sizeof(secp256k1_ecdsa_signature)*2;
    unsigned char *sig_out = (unsigned char *)malloc(sig_len);

    if (secp256k1_ecdsa_signature_serialize_der(ctx, sig_out, &sig_len, &sig) == 0) {
        printf("Unable to serialize the signature\n");
        return 1;
    }

    char *sig_hex = (char *)malloc(sig_len * 2);

    for (int i = 0, j = 0; i < strlen((const char*)sig_out); ++i, j += 2) {
        sprintf(sig_hex + j, "%02x", sig_out[i] & 0xff);
    }

    printf("Signature: %s\n", sig_hex);

    if(secp256k1_ecdsa_verify(ctx, &sig, msg, &pubkey)==0){
        printf("Unable to verify signature\n");
    } else {
        printf("Signature verified\n");
    }

    return 0;
}

Fixed bugs from original source.

Thank you!