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Andrew
Andrew

Reputation: 7883

Storing encryption key within iOS app?

I need to store an encryption key within my app, so that it can use the same key to encrypt and upload data, and download and decrypt data, from a public store. That way, the data can't be read by any other party in between.

What I'm concerned about is the potential for somebody to hijack my app. Once my app has been archived, would it be possible for someone to read a hardcoded encryption key held within the app?

Upvotes: 0

Views: 2745

Answers (2)

zaph
zaph

Reputation: 112865

If the key is in the app bundle there is a chance it can be discovered and doing this is not secure. As @Cristik states authenticate the user to the server and download the key at that point.

To secure the key the best you can do is to save the key in the Keychain.

Protecting against the owner of the device is very difficult and falls more under DRM.

Protecting against an non-owner depends on the owner having set a good passcode/password.

Protecting against data in transit (upload/download) is easy, use https, ensure the server is current (TLS 1.2 and Perfect Forward Secrecy) and pin the server certificate in the app.

Update:

In the ipa only the executable files are encrypted so other files can be accessed from the download. If a file is encrypted the attacker will need the encryption key and that can be strong: random bytes.

But the app needs the encryption key so the problem is how can the app know the key and not an attacker. Encryption does increase the work factor be the need to obtain the key.

There are disassemble tools so if the key is in the code it can be found by an experienced attacker.

If the key comes from a server it is not coded into the app so the work factor again increases. A MITM attack can be used to see the key in transit and pinning the certificate and using current https best practices can mitigate this attack vector.

Finally the key is in RAM memory at the time of decryption and can be found but again the work factor is increased.

In general what is necessary to protect data at the highest levels is complicated, requires special hardware and physical security.

Bottom line: determine the level of attacker you are defending against and the value of the data; code to that level. Do not underestimate the attacker.

Upvotes: 3

Cristik
Cristik

Reputation: 32873

Instead of storing the encryption key within the application bundle, you can request it from a server via a secure connection (HTTPS), and then save it in keychain for later retrieval.

You can add more security layers to the https connection by adding SSL pinning or/and other security measures.

Plus, you can generate different encryption keys every time the user logins, and if the store API supports it, you can invalidate all keys generated for a user if for example his phone is stolen.

Upvotes: 1

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