NAME

ne_ssl_set_verify - register an SSL certificate verification callback

SYNOPSIS

#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);

DESCRIPTION

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

NE_SSL_EXPIRED

NE_SSL_IDMISMATCH

NE_SSL_UNTRUSTED

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.

RETURN VALUE

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).

EXAMPLES

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");


  ...
}

SEE ALSO

ne_ssl_trust_cert, ne_ssl_readable_dname, ne_ssl_cert_subject

AUTHOR

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

COPYRIGHT