Apple won't provide experts with details of encryption architecture, so what it means by 'cannot decrypt' data is unclear, expert says
Homomorphic encryption-based method makes it possible to process data without having to decrypt it
Bitcoin sales all recorded to a public ledger, meaning payments made to a company could lead to tracking of later payments made to that address
Electronic tattoos and pills that make the body itself a password would create their own unique challenges, security experts warn
