Lately I've been thinking about how to integrate Ethereum with other non-Ethereum systems. Would it be a bad idea to import and Ethereum keypair into an external (mobile/desktop) application, which could be used to verify one's Ethereum identity/conduct transactions?
Users would authenticate by using one's private key in response to a generated random challenge (decrypt or sign it), or use the embedded private key to sign Ethereum transactions and send them to some external system.
Would that be in line with the spirit and the general idea of Ethereum and/or pose a security threat to users?
The value of using such an app would be the ability to externally prove the ownership of an Ethereum account. It could be used to prove an ownership of an asset or transaction execution.
It would be possible to integrate smart contracts into existing non-Ethereum systems.