SSL Pinning with AFNetworking 3.0

Question

I am using AFNetworking 3.0 . I have webserver with a https certificate which is signed by Global Sign. I want to add Certificate pinning to my iOS app. My code as below:

- (AFSecurityPolicy*)customSecurityPolicy{

AFSecurityPolicy *securityPolicy = [AFSecurityPolicy policyWithPinningMode:AFSSLPinningModeNone];
NSString *cerPath = [[NSBundle mainBundle] pathForResource:@"server" ofType:@"cer"];
NSData *certData = [NSData dataWithContentsOfFile:cerPath];
[securityPolicy setAllowInvalidCertificates:NO];
[securityPolicy setValidatesDomainName:YES];

//securityPolicy.validatesCertificateChain = NO;
[securityPolicy setPinnedCertificates:[NSKeyedUnarchiver unarchiveObjectWithData:certData]];

return securityPolicy;
}

My client code:

NSString *url = SERVER_URL;
AFHTTPSessionManager *manager = [AFHTTPSessionManager manager];
manager.responseSerializer.acceptableContentTypes = [NSSet setWithObject:@"application/json"];
manager.securityPolicy = [utils customSecurityPolicy];
[manager GET:url parameters:nil progress:nil success:^(NSURLSessionTask *task, id responseObject) {

    NSLog(@"JSON: %@", responseObject);


} failure:^(NSURLSessionTask *operation, NSError *error) {
    NSLog(@"Error: %@", error);

}];

We use burp suite for the man-in-the-middle proxy, we are able to interrupt the request and monitor the contents of the request.

So, How can I implement certificate pinning properly?

Answer 1

This is valid question that lies outside AFNetworking, the only things you find is the way on which library you are using implements curl --cacert operation.

In the specific case of AFNetworking , I have this situation:

let sessionManager = AFHTTPSessionManager()
sessionManager.responseSerializer = AFJSONResponseSerializer()
sessionManager.requestSerializer = AFJSONRequestSerializer()
let configuration = ServiceConfiguration.sharedInstance.configuration
if let policy = configuration?.getSecurityPolicy()?.policy() as? AFSecurityPolicy {
    sessionManager.securityPolicy = policy
}

Method getSecurityPolicy returns an optional object of RequestSecurityPolicy (that is a protocol).

To make an AFSecurityPolicy I have:

import AFNetworking

class SSLPinningPolicy: NSObject, RequestSecurityPolicy {

    // MARK: - Private properties -

    private var certificatesDictionary: [String: Data] = [:]

    // MARK: - Initilizers -

    init(certicatePaths: [String]) {
        super.init()
        for path in certicatePaths {
            if let certPath = Bundle.main.path(forResource: path, ofType: "der") {
                let url = URL(fileURLWithPath: certPath)
                do {
                    let data = try Data(contentsOf: url)
                    self.certificatesDictionary[path] = data
                } catch {

                }
            }
        }
    }

    // MARK: - RequestSecurityPolicy delegates -

    func policy() -> AnyObject {
        let policy = AFSecurityPolicy(pinningMode: .certificate)
        policy.allowInvalidCertificates = true
        policy.pinnedCertificates = self.certificates()
        return policy
    }

    func certificates() -> Set<Data> {
        return Set(self.certificatesDictionary.map { $0.value })
    }

}

Plus

In order to convert my certificate from .pem to .der you can simply use openssl from your shell:

openssl x509 -outform der -in MyCertificate.pem -out MyCertificate.der