tamper-proof 
adjective
Made so that it cannot be interfered with or changed: driving licences with tamper-proof colour photographs...
- It's weatherproof and tamper-proof, and there's no reason why this ring couldn't be used as a ‘wallet’ for digital currency.
- The minister has lectured all that would listen that his new system is tamper-proof and idiot-proof.
- Apart from saving 9,000 tons of ballot papers the method was much more error-free and tamper-proof and, very importantly, less vulnerable to the violence and fraud problems of previous elections.