CODEWITHSUNDEEP
sslencryptionopenssl
Marko Bencik
Marko Bencik

Reputation: 396

SSL_write default behavior

Currently I'm working on some basic OpenSSL. I'm confused about the basic behavior of SSL_write and SSL_read. In the documentation it is not clearly explained how the data is encrypted / decrypted. What I mean? Is the SSL_write, once the SSL_CTX is set and file descriptor assigned, by default encrypting the data or calling the encryption function, or does this have to be done by hand? Do I have to call some encryption function explicitly? Is the same true for the SSL_read? I need a deeper understanding of what SSL_write / read do automatically and what not, or sources where I can fall back to if I'm having issues.

Here is an example that I'm working with.

Example:

    SSL *ssl;

    int client = accept(server, (struct sockaddr*)&addr, &len);  /* accept connection as usual */
    printf("Connection: %s:%d\n",inet_ntoa(addr.sin_addr), ntohs(addr.sin_port));
    ssl = SSL_new(ctx);              /* get new SSL state with context */
    SSL_set_fd(ssl, client);      /* set connection socket to SSL state */
    Servlet(ssl);         /* service connection */

Servlet calls

void Servlet(SSL* ssl) 
{
    char buf[1024];
    char reply[1024];
    int sd, bytes;
    const char* HTMLecho="<html><body><pre>%s</pre></body></html>\n\n";

    if ( SSL_accept(ssl) == FAIL )     /* do SSL-protocol accept */
        ERR_print_errors_fp(stderr);
    else
    {
        ShowCerts(ssl);        /* get any certificates */
        bytes = SSL_read(ssl, buf, sizeof(buf)); /* get request */
        if ( bytes > 0 )
        {
            buf[bytes] = 0;
            printf("Client msg: \"%s\"\n", buf);
            sprintf(reply, HTMLecho, buf);   /* construct reply */
            SSL_write(ssl, reply, strlen(reply)); /* send reply */
        }
        else
            ERR_print_errors_fp(stderr);
    }
    sd = SSL_get_fd(ssl);       /* get socket connection */
    SSL_free(ssl);         /* release SSL state */
    close(sd);          /* close connection */
}

Upvotes: 0

Views: 772

Answers (1)

Steffen Ullrich
Steffen Ullrich

Reputation: 123270

Do I have to call some encryption function explicitly, is the same true for the SSL_read?

No. Encryption is handled within SSL_write automatically as is decryption in SSL_read. Both use the SSL structure which contains the necessary encryption keys once the TLS handshake is finished.

... sources where I can fall back to if I'm having issues

This depends on the issues you have. Both SSL_read and SSL_write have documentation. There are also easy to find examples. Being able to use a search engine helps also a lot to find more information. And StackOverflow is a good place to get help if things don't work as expected.

Upvotes: 3

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