Checking a Public Key in canAuthenticateAgainstProtectionSpace - iphone

Question

I have been asked to check the public key against a known value in canAuthenticateAgainstProtectionSpace ( a delegate callback of NSURLConnection )
This is what I have so far:
- (BOOL)connection:(NSURLConnection *)connection
canAuthenticateAgainstProtectionSpace:(NSURLProtectionSpace *)protectionSpace
{
SecKeyRef publicKey = SecTrustCopyPublicKey([protectionSpace serverTrust]);
NSLog(#"%#",SecTrustCopyPublicKey([protectionSpace serverTrust]));
return YES;
}
How can I compare the public key against a known value?
The NSLog produces: <SecKeyRef: 0x687c000> which isn't vary useful.

Answer 1

Incase anyone cares, the solution was to check the certificatie byte for byte with a certificate saved on the bundle.
- (BOOL)connection:(NSURLConnection *)connection canAuthenticateAgainstProtectionSpace:(NSURLProtectionSpace *)protectionSpace
{
SecTrustRef trust = [protectionSpace serverTrust];
SecCertificateRef certificate = SecTrustGetCertificateAtIndex(trust, 0);
NSData* ServerCertificateData = (NSData*) SecCertificateCopyData(certificate);
// Check if the certificate returned from the server is identical to the saved certificate in
// the main bundle
BOOL areCertificatesEqual = ([ServerCertificateData
isEqualToData:[MyClass getCertificate]]);
[ServerCertificateData release];
if (!areCertificatesEqual)
{
NSLog(#"Bad Certificate, canceling request");
[connection cancel];
}
// If the certificates are not equal we should not talk to the server;
return areCertificatesEqual;
}

Answer 2

Note that SecCertificateCopyData returns the certificate in it's "DER" form, Distinguished Encoding Rules. So you need to incorporate the certificate in your App in that form, and not as a pem or whatever format. To convert a certificate to DER with openssl use the command: openssl x509 -in server.crt -out server.der -outform DER