main.c

#include "openssl/evp.h"
#include <stdio.h>
#include <string.h>

void SHA256(const char *message, char *digest, unsigned int siglen)
{
    EVP_MD_CTX *mdctx;
    const EVP_MD *md;
    unsigned char md_value[EVP_MAX_MD_SIZE];
    unsigned int i;

    OpenSSL_add_all_digests();
    md = EVP_get_digestbyname("sha256");

    if(!md) {
        printf("Unknown message digest\n");
        return;
    }

    mdctx = EVP_MD_CTX_create();
    EVP_DigestInit_ex(mdctx, md, NULL);
    EVP_DigestUpdate(mdctx, message, strlen(message));
    EVP_DigestFinal_ex(mdctx, md_value, &siglen);
    EVP_MD_CTX_destroy(mdctx);

    for (i = 0; i < siglen; i++) {
        snprintf(&digest[i*2], 3, "%02x", md_value[i]);
    }
    EVP_cleanup();
    return;

}

int main() {
    char buf[33], sSignature[65], sChallenge[98];
    char *password = "admin";
    strcpy(buf, "60d11a81a26df3738026b1839644a1ae");
    printf("buf now is: %s\n", buf);
	SHA256(password, sSignature, sizeof(sSignature));
    printf("calculated hash of password is: %s\n", sSignature);
	snprintf(sChallenge, sizeof(sChallenge), "%s%s", buf, sSignature);
    printf("challenge is: %s\n", sChallenge);
	SHA256(sChallenge, sSignature, sizeof(sSignature));
    printf("calculated hash is: %s\n", sSignature);
    return 0;
}