WEBVTT

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Welcome. This tutorial covers how the library detects a repackaged or tampered copy of your own app.

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There are four tamper signals: two on Android, and two on iOS.

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They are all opt-in, because only you know what a genuine build of your app looks like.

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To tamper with your app, an attacker first obtains it: by decoding the Android package, or by dumping a decrypted iOS binary from memory.

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Then they patch it: remove your security checks, add ads, or bolt on malware.

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Rebuilding strips the original signature, so they must re-sign with their own key. That is the weak point.

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Finally they distribute the clone through sideloading, enterprise certificates, or look-alike stores.

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On Android, the signature check compares the app's signing certificate with the ones you expect.

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It reads the certificates from the package manager, honouring key rotation on newer Android versions, and hashes each one with SHA-256.

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If none of the digests is in your expected list, the app was re-signed, because repackaging always strips the original signature.

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Get the digest with keytool, or from the Play Console app signing page. For Play builds, use the Play App Signing key.

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The installer check asks who installed the app. A trusted store, like Google Play, is the normal source.

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You list the allowed installers, for example com.android.vending. A null or unknown installer, such as adb or a browser download, counts as untrusted.

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Enable it in release builds only, because every debug install through adb will fail it.

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The installer name can be spoofed by a session that claims to be the Play Store, so this is a medium-strength signal.

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On iOS, the Team ID check reads your app's signing team, and it does so through the keychain.

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It adds a throwaway keychain item, reads back its access group, whose prefix is the Team ID, and deletes the item.

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A re-signed build carries the attacker's team ID, not yours, so pinning the expected team catches sideloaded and enterprise-signed clones.

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Debug builds signed with a personal team will mismatch, so enable it for release builds.

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The decrypted binary check asks whether the main executable is still encrypted by Apple's FairPlay.

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It walks the Mach-O load commands and reads the encryption info. A cryptid of zero, or no such command, means the binary is plaintext.

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Reverse engineers get a plaintext binary by dumping it from memory after FairPlay decrypts it, then re-sign and redistribute it.

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Only enable it for App Store and TestFlight builds, never debug or ad-hoc builds, which are not encrypted.

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On Android, pass expected signing certificates: the SHA-256 digests, in hex, with or without colons.

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Pass allowed installers, such as the Play Store, and only in release builds.

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On iOS, pass your expected Team IDs, taken from your Apple Developer account.

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And set require encrypted binary to true, for App Store and TestFlight builds only. None of these run unless you pass them, and they never make a complete report incomplete.

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The signature check trusts the OS's answer. On a rooted phone, an attacker can hook the package manager and return your real certificate.

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The installer check can be spoofed by an install session that claims to come from the Play Store.

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The team ID check can be fooled on a jailbroken device by hooking the keychain query or the comparison.

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And the decrypted binary check can be beaten by patching the cryptid byte back to a non-zero value.

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Let us recap. One: repackaging always means re-signing, and that is the weak point we pin.

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Two: on Android, check the signing certificate and the installer.

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Three: on iOS, check the Team ID and whether the binary is still encrypted.

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Four: on a rooted or jailbroken device these answers can be faked, so back them with server-side attestation.

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Thanks for watching. The opt-in options are documented in the README, under tamper checks.

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Next, watch the debugger and emulator video.