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 seed-phrase 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 .