To prove possession of a private key, one needs only to sign something with that key (this is how SSH key auth works). This is how things like the macOS Secure Enclave operate - the private key is stored in a separate hardware chip that only exposes an interface to sign something with that key, never to actually present the key. To obtain the key would require having physical access to the computer, ripping it open, and performing advanced deconstruction and analysis of that chip.
replyI dont want to be rude, I am aware of the operational semantics. Getting what you want to be signed with the key is the external channel operation I was referring to. In this particular case, somehow the attack vector being disabled is the actual private key being locked from any export. This gives a sense of security, however the channel abuse can bypass the security.
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