TrustKit

TrustKit is an open source framework that makes it easy to deploy SSL public key pinning and reporting in any iOS 12+, macOS 10.13+, tvOS 12+ or watchOS 4+ App; it supports both Swift and Objective-C Apps.

If you need SSL pinning/reporting in your Android App. we have also released TrustKit for Android at https://github.com/datatheorem/TrustKit-Android.

Overview

TrustKit provides the following features:

• Simple API to configure an SSL pinning policy and enforce it within an App. The policy settings are heavily based on the HTTP Public Key Pinning specification.
• Sane implementation by pinning the certificate's Subject Public Key Info, as opposed to the certificate itself or the public key bits.
• Reporting mechanism to notify a server about pinning validation failures happening within the App, when an unexpected certificate chain is detected. This is similar to the report-uri directive described in the HPKP specification. The reporting mechanism can also be customized within the App by leveraging pin validation notifications sent by TrustKit.
• Auto-pinning functionality by swizzling the App's NSURLConnection and NSURLSession delegates in order to automatically add pinning validation to the App's HTTPS connections; this allows deploying TrustKit without even modifying the App's source code.

Getting Started

• Read the Getting Started guide.
• Check out the API documentation.
• TrustKit was initially released at Black Hat USA 2015 and was also featured on PayPal's engineering blog.

Sample Usage

Deploying SSL pinning in the App requires initializing TrustKit with a pinning policy (domains, Subject Public Key Info hashes, and additional settings).

The policy can be configured within the App's Info.plist:

Alternatively, the pinning policy can be set programmatically:

    NSDictionary *trustKitConfig =
  @{
    kTSKSwizzleNetworkDelegates: @NO,
    kTSKPinnedDomains : @{
            @"www.datatheorem.com" : @{
                    kTSKExpirationDate: @"2017-12-01",
                    kTSKPublicKeyHashes : @[
                            @"HXXQgxueCIU5TTLHob/bPbwcKOKw6DkfsTWYHbxbqTY=",
                            @"0SDf3cRToyZJaMsoS17oF72VMavLxj/N7WBNasNuiR8="
                            ],
                    kTSKEnforcePinning : @NO,
                    },
            @"yahoo.com" : @{
                    kTSKPublicKeyHashes : @[
                            @"TQEtdMbmwFgYUifM4LDF+xgEtd0z69mPGmkp014d6ZY=",
                            @"rFjc3wG7lTZe43zeYTvPq8k4xdDEutCmIhI5dn4oCeE=",
                            ],
                    kTSKIncludeSubdomains : @YES
                    }
            }};
    
    [TrustKit initSharedInstanceWithConfiguration:trustKitConfig];

The policy can also be set programmatically in Swift Apps:

        let trustKitConfig = [
            kTSKSwizzleNetworkDelegates: false,
            kTSKPinnedDomains: [
                "yahoo.com": [
                    kTSKExpirationDate: "2017-12-01",
                    kTSKPublicKeyHashes: [
                        "JbQbUG5JMJUoI6brnx0x3vZF6jilxsapbXGVfjhN8Fg=",
                        "WoiWRyIOVNa9ihaBciRSC7XHjliYS9VwUGOIud4PB18="
                    ],]]] as [String : Any]
        
        TrustKit.initSharedInstance(withConfiguration:trustKitConfig)

After TrustKit has been initialized, a TSKPinningValidator instance can be retrieved from the TrustKit singleton, and can be used to perform SSL pinning validation in the App's network delegates. For example in an NSURLSessionDelegate:

- (void)URLSession:(NSURLSession *)session 
              task:(NSURLSessionTask *)task 
didReceiveChallenge:(NSURLAuthenticationChallenge *)challenge 
 completionHandler:(void (^)(NSURLSessionAuthChallengeDisposition disposition, NSURLCredential *credential))completionHandler {
{
    TSKPinningValidator *pinningValidator = [[TrustKit sharedInstance] pinningValidator];
    // Pass the authentication challenge to the validator; if the validation fails, the connection will be blocked
    if (![pinningValidator handleChallenge:challenge completionHandler:completionHandler])
    {
        // TrustKit did not handle this challenge: perhaps it was not for server trust
        // or the domain was not pinned. Fall back to the default behavior
        completionHandler(NSURLSessionAuthChallengePerformDefaultHandling, nil);
    }
}

For more information, see the Getting Started guide.

Credits

TrustKit is a joint-effort between the mobile teams at Data Theorem and Yahoo. See AUTHORS for details.

License

TrustKit is released under the MIT license. See LICENSE for details.