generate RSA key pair and write them to a file (openssl)

rsa_keygen.c

/**
 * Author: Devendra Naga (devendra.aaru@gmail.com)
 * License: MIT
 * Code failure paths are not taken care.. this program is only for demonstration purposes
 */
#include <stdio.h>
#include <openssl/rsa.h>
#include <openssl/evp.h>
#include <openssl/pem.h>

int main()
{
    char *pubkey = "./rsa_2048.key";
    char *privkey = "./rsa_2048_p.key";
    EVP_PKEY_CTX *ctx;

    ctx = EVP_PKEY_CTX_new_id(EVP_PKEY_RSA, NULL);
    if (!ctx) {
        return -1;
    }

    int ret;

    ret = EVP_PKEY_keygen_init(ctx);
    if (ret != 1) {
        return -1;
    }

    ret = EVP_PKEY_CTX_set_rsa_keygen_bits(ctx, 2048);
    if (ret != 1) {
        return -1;
    }

    EVP_PKEY *key;

    ret = EVP_PKEY_keygen(ctx, &key);
    if (ret != 1) {
        return -1;
    }

    FILE *fp = fopen(privkey, "w");
    if (!fp) {
        return -1;
    }

    ret = PEM_write_PrivateKey(fp, key, NULL, NULL, 0, NULL, NULL);
    if (ret != 1) {
        return -1;
    }

    fclose(fp);

    fp = fopen(pubkey, "w");
    if (!fp) {
        return -1;
    }

    ret = PEM_write_PUBKEY(fp, key);
    if (ret != 1) {
        return -1;
    }
    
    fclose(fp);

    return 0;
}