Hi everyone,
I’m working on an iOS app that uses biometric authentication to access secure keychain items and private keys stored in the Secure Enclave with some data encryption/decryption with those keys. My goal is to minimize the number of biometric prompts by reusing the authentication result within a short time window.
I have the following setup:
- When writing the biometry-restricted keychain items and Secure Enclave keys, I use LAContext with the property LATouchIDAuthenticationMaximumAllowableReuseDuration = 1 minute, and I pass this context as the kSecUseAuthenticationContext field in the query.
- When retrieving these items later (in a synchronous sequence upon app launch), I pass the same instance of LAContext as the kSecUseAuthenticationContext field.
The issue:
- If I unlock my device and the biometric reuse time has not expired (i.e., less than 1 minute), the first two actions (keychain item retrieval and Secure Enclave key retrieval) do not prompt for Face ID.
- However, when I attempt to decrypt data with the private key using SecKeyCreateDecryptedData, I’m prompted for Face ID even if the biometric reuse time is still valid.
- If the biometric reuse time has expired (more than 1 minute since last authentication), I get prompted for Face ID on the first action (keychain retrieval), and subsequent actions (including data decryption) reuse that biometric result.
Question:
Does this behavior mean that SecKeyCreateDecryptedData ignore the LATouchIDAuthenticationMaximumAllowableReuseDuration property of LAContext, causing an additional biometric prompt during decryption with the private key? Or is there another reason for this behavior? Is there a way to make the biometric result reusable across all these actions, including decryption?
Thank you!