Why fiddler can not decrypt App Store app's https traffic on iPhone, but the others apps can be

[Zhaoxiang Wei]

I want to capture some data from App store on iphone (iOS9), but it doesn't works.

I tried to capture the other apps and it works, and I used safari open a https website, it still works.

Why?

[EricLaw]

The AppStore and a number of other applications use a technique called "Certificate Pinning" to detect when their traffic has been intercepted. See http://fiddler.wikidot.com/certpinning for details and potential workarounds.