Manpages - ne_ssl_set_verify.3

ne_ssl_set_verify - register an SSL certificate verification callback

  #include <ne_session.h>

typedef int ne_ssl_verify_fn(void **/userdata/, int failures, const ne_ssl_certificate */cert/);*

void ne_ssl_set_verify(ne_session **/session/, ne_ssl_verify_fn verify_fn, void */userdata/);*

To enable manual SSL certificate verification, a callback can be registered using ne_ssl_set_verify. If such a callback is not registered, when a connection is established to an SSL server which does not present a certificate signed by a trusted CA (see ne_ssl_trust_cert), or if the certificate presented is invalid in some way, the connection will fail.

When the callback is invoked, the failures parameter gives a bitmask indicating in what way the automatic certificate verification failed. The value is equal to the bit-wise OR of one or more of the following constants (and is guaranteed to be non-zero):

NE_SSL_NOTYETVALID

The certificate is not yet valid.

NE_SSL_EXPIRED

The certificate has expired.

NE_SSL_IDMISMATCH

The hostname used for the session does not match the hostname to which the certificate was issued.

NE_SSL_UNTRUSTED

The Certificate Authority which signed the certificate is not trusted.

Note that if either of the NE_SSL_IDMISMATCH or NE_SSL_UNTRUSTED failures is given, the connection may have been intercepted by a third party, and must not be presumed to be “secure”.

The cert parameter passed to the callback represents the certificate which was presented by the server. If the server presented a chain of certificates, the chain can be accessed using ne_ssl_cert_signedby. The cert object given is not valid after the callback returns.

The verification callback must return zero to indicate that the certificate should be trusted; and non-zero otherwise (in which case, the connection will fail).

The following code implements an example verification callback, using the dump_cert function from ne_ssl_cert_subject to display certification information. Notice that the hostname of the server used for the session is passed as the userdata parameter to the callback.

    static int
    my_verify(void *userdata, int failures, const ne_ssl_certificate *cert)
    {
      const char *hostname = userdata;

      dump_cert(cert);

      puts("Certificate verification failed - the connection may have been "
           "intercepted by a third party!");

      if (failures & NE_SSL_IDMISMATCH) { 
        const char *id = ne_ssl_cert_identity(cert);
        if (id) 
          printf("Server certificate was issued to %s not %s.\n",
                 id, hostname);
        else
          printf("The certificate was not issued for %s\n", hostname);
      }

      if (failures & NE_SSL_UNTRUSTED)
        puts("The certificate is not signed by a trusted Certificate Authority.");

      /* ... check for validity failures ... */

      if (prompt_user())
        return 1; /* fail verification */
      else
        return 0; /* trust the certificate anyway */
    }

    int
    main(...)
    {
      ne_session *sess = ne_session_create("https", "some.host.name", 443);
      ne_ssl_set_verify(sess, my_verify, "some.host.name");
      ...
    }

ne_ssl_trust_cert, ne_ssl_readable_dname, ne_ssl_cert_subject

Joe Orton <neon@lists.manyfish.co.uk>

Author.