To make transactions secure, we rely on blockchain encryption. It ensures transparency, privacy, validity and, to a large degree, prevents tampering. You are the only holder of your cryptographic (private) keys. They are generated and stored only on your device. While your private key and master password are secure, your funds are under your control only.
For additional security we are working on Surf cold wallet (TON Labs Security Card) and on a multi-signature function for access and transaction confirmation in Surf. Stay tuned for news about the Security card.
More information about security in Surf can be found here https://medium.com/freeton/how-to-keep-my-cryptocurrency-safe-in-surf-a5d5c202b38d and .