TLS Validation Failure

Question

Created Mar ’22

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Hi, my application has an NSAllowsArbitraryLoads flag in Info.plist which is set to YES. I want to enable ATS checks and therefore is trying to disable NSAllowsArbitraryLoads option. But I faced with problem.

I am completely delete NSAppTransportSecurity section from Info.plist and then run the application. When I use dev stand everything is okay and works good.

But since I've switched my application to production stand – any internet connection is failed with following error:

2022-03-30 03:23:17.511459+0300 *[10271:4471591] Connection 77: strict TLS Trust evaluation failed(-9802)

2022-03-30 03:23:17.511549+0300 *[10271:4471591] Connection 77: TLS Trust encountered error 3:-9802

2022-03-30 03:23:17.511629+0300 *[10271:4471591] Connection 77: encountered error(3:-9802)

2022-03-30 03:23:17.512571+0300 *[10271:4471591] Task <4F7E00BD-2CB7-4055-A8DF-69CD9F562800>.<54> HTTP load failed, 0/0 bytes (error code: -1200 [3:-9802])

Error Domain=NSURLErrorDomain Code=-1200 "An SSL error has occurred and a secure connection to the server cannot be made." UserInfo={NSLocalizedRecoverySuggestion=Would you like to connect to the server anyway?, _kCFStreamErrorDomainKey=3,
...
// certificate chain

I've already red a lot of topics about TLS validation and checked some hypothesis. For example I've checked this:

openssl s_client -connect ***.***.com:443

And the returned info is said, that server meets ATS requirements

Server public key is 2048 bit
Protocol  : TLSv1.2 (ok)
Cipher    : ECDHE-RSA-CHACHA20-POLY1305 (ok)
Verify return code: 0 (ok)

Another interesting point, is that if i use a corporate VPN – everything works perfect even for production stand. But when corporate VPN is switched off – error comes back. The main difference, that i realized – changed certificates list for this cases.

Currently I have no idea what's going wrong, because it seems, that backend fully support ATS requirements. Any idea will be great!

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Answer 1

Systems Engineer OP

Apple

Mar ’22

Nice work enabling App Transport Security in your app. All apps should take advantage of this feature.

In regards to your error:

2022-03-30 03:23:17.511459+0300 *[10271:4471591] Connection 77: strict TLS Trust evaluation failed(-9802)

2022-03-30 03:23:17.511549+0300 *[10271:4471591] Connection 77: TLS Trust encountered error 3:-9802

This is a pretty general TLS error, but since the error specifically mentions, "Trust evaluation failed," then I would take a look at you certificate chain to ensure that a chain of trust can be established on your server's certificate chain. You may also want to take a look at the leaf certificate on your server to make sure it derives from a trusted root certificate in the iOS trust store.

Next, you might want to take a look at Quinn's TLS for App Developers post. This post has some great information on how TLS works and what is expected of both the client and server. Note the links at the bottom as these are especially helpful for understanding Apple's policies around certificate transparency, certificate validity periods, and the requirements for trusted certificates.

Lastly, if all else fails, you can always take a packet trace to find out where the breakdown is between your client and server. Checkout this article for more information.

Matt Eaton
DTS Engineering, CoreOS
meaton3@apple.com

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