Determining if a block of data was signed on the Secure Enclave

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CMDdev OP

Created 2w

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Hello,

I'm exploring the Secure Enclave APIs, and I'm wondering if it's possible to "cryptographically" determine if a block of data was signed on the Secure Enclave.

When I sign a block of data using the Secure Enclave (which implies using a key pair automatically generated by the enclave) and distribute the public key to others, is there any way to verify if the message was encrypted on it / its private key was generated by it? In other words, what I'm trying to achieve is to make sure that the public key hasn't been tampered with until it reaches its destination (including on-device threats, since otherwise I could've used a normal keychain item, perhaps?).

For the purpose of this example, I'm not necessarily interested in figuring out if the key was signed on a certain device's enclave, but rather on any Secure Enclave. So, using something derived from the enclave's GID Key (described in the Apple Platform Security guide) would work for this.

Answered by DTS Engineer in 820949022

I don’t see how that’d even be theoretically possible. When you signed on the SE, the signing key is a standard P-256 key. The signature it produces will be the same format as a signature produced by any other P-256 key. The only difference is that this specific P-256 key is only accessible to the SE.

what I'm trying to achieve is to make sure that the public key hasn't been tampered with until it reaches its destination

I recommend that you explore App Attest.

Share and Enjoy
—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

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Answer 1

DTS Engineer OP

Apple

1w

Accepted Answer

I don’t see how that’d even be theoretically possible. When you signed on the SE, the signing key is a standard P-256 key. The signature it produces will be the same format as a signature produced by any other P-256 key. The only difference is that this specific P-256 key is only accessible to the SE.

what I'm trying to achieve is to make sure that the public key hasn't been tampered with until it reaches its destination

I recommend that you explore App Attest.

Share and Enjoy
—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

0

Answer 2

CMDdev OP

1w

Thank you for your response, Quinn!

I don’t see how that’d even be theoretically possible.

Perhaps something like signing with a public-private key common to all SEs. But that kind-of-diminishes the randomness of that specific P-256 key. Theoretically, if kept secret, the private key should be secure.

I recommend that you explore App Attest.

That seems to address this, thanks!

Since this is for the Swift Student Challenge, I think I won't be able to use it (my "demo" playground wouldn't have a specific app ID, and it also does not have internet access), but I think I can mention this as a further security enhancement in a real-world app.

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