Simple TLS Server

Simple TLS Server

The code below is a complete implementation of a minimal TLS server.

#include <stdio.h>
#include <unistd.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <openssl/ssl.h>
#include <openssl/err.h>

int create_socket(int port)
{
    int s;
    struct sockaddr_in addr;

    addr.sin_family = AF_INET;
    addr.sin_port = htons(port);
    addr.sin_addr.s_addr = htonl(INADDR_ANY);

    s = socket(AF_INET, SOCK_STREAM, 0);

    if (bind(s, (struct sockaddr*)&addr, sizeof(addr)) < 0) {
	perror("Unable to bind");
	exit(EXIT_FAILURE);
    }

    if (listen(s, 1) < 0) {
	perror("Unable to listen");
	exit(EXIT_FAILURE);
    }

    return s;
}

void init_openssl()
{ 
    SSL_load_error_strings();	
    OpenSSL_add_ssl_algorithms();
}

void cleanup_openssl()
{
    EVP_cleanup();
}

SSL_CTX *create_context()
{
    const SSL_METHOD *method;
    SSL_CTX *ctx;

    method = TLSv1_server_method();

    ctx = SSL_CTX_new(method);
    if (!ctx) {
	perror("Unable to create SSL context");
	ERR_print_errors_fp(stderr);
	exit(EXIT_FAILURE);
    }

    return ctx;
}

int main(int argc, char **argv)
{
    int sock;
    SSL_CTX *ctx;

    init_openssl();
    ctx = create_context();

    /* Set the key and cert */
    if (SSL_CTX_use_certificate_file(ctx, "cert.pem", SSL_FILETYPE_PEM) < 0) {
        ERR_print_errors_fp(stderr);
	exit(EXIT_FAILURE);
    }

    if (SSL_CTX_use_PrivateKey_file(ctx, "key.pem", SSL_FILETYPE_PEM) < 0 ) {
        ERR_print_errors_fp(stderr);
	exit(EXIT_FAILURE);
    }

    sock = create_socket(4433);

    /* Handle connections */
    while(1) {
        struct sockaddr_in addr;
        uint len = sizeof(addr);
        SSL *ssl;
        const char reply[] = "test\n";

        uint client = accept(sock, (struct sockaddr*)&addr, &len);
        ssl = SSL_new(ctx);
        SSL_set_fd(ssl, client);

        if (SSL_accept(ssl) <= 0) {
            ERR_print_errors_fp(stderr);
        }
        else {
            SSL_write(ssl, reply, strlen(reply));
        }

        SSL_free(ssl);
        close(client);
    }

    close(sock);
    SSL_CTX_free(ctx);
    cleanup_openssl();
}