//compiled with gcc -g -lssl -UOPENSSL_NO_EC SO2228860.c -lcrypto
#include <openssl/ec.h>      // for EC_GROUP_new_by_curve_name, EC_GROUP_free, EC_KEY_new, EC_KEY_set_group, EC_KEY_generate_key, EC_KEY_free
#include <openssl/ecdsa.h>   // for ECDSA_do_sign, ECDSA_do_verify
#include <openssl/obj_mac.h> // for NID_secp192k1
static int create_signature(unsigned char* hash)
    int function_status = -1;
    EC_KEY *eckey=EC_KEY_new();
    if (NULL == eckey)
        printf("Failed to create new EC Key\n");
        function_status = -1;
        EC_GROUP *ecgroup= EC_GROUP_new_by_curve_name(NID_secp192k1);
        if (NULL == ecgroup)
            printf("Failed to create new EC Group\n");
            function_status = -1;
            int set_group_status = EC_KEY_set_group(eckey,ecgroup);
            const int set_group_success = 1;
            if (set_group_success != set_group_status)
                printf("Failed to set group for EC Key\n");
                function_status = -1;
                const int gen_success = 1;
                int gen_status = EC_KEY_generate_key(eckey);
                if (gen_success != gen_status)
                    printf("Failed to generate EC Key\n");
                    function_status = -1;
                    ECDSA_SIG *signature = ECDSA_do_sign(hash, strlen(hash), eckey);
                    if (NULL == signature)
                        printf("Failed to generate EC Signature\n");
                        function_status = -1;
                        int verify_status = ECDSA_do_verify(hash, strlen(hash), signature, eckey);
                        const int verify_success = 1;
                        if (verify_success != verify_status)
                            printf("Failed to verify EC Signature\n");
                            function_status = -1;
                            printf("Verifed EC Signature\n");
                            function_status = 1;
            EC_GROUP_free(ecgroup);
        EC_KEY_free(eckey);
  return function_status;