Signing Flow and MPC Overview
How Surf executes transactions securely without ever holding your private keys
At the core of Surf’s security model is a strict separation between:
Decision making Execution permission Cryptographic signing
Surf never holds user private keys. Surf never has unilateral signing authority. Surf never becomes a custodian.
Instead, transaction execution follows a controlled signing flow enforced through MPC and vault-scoped permissions.
What is MPC?
MPC stands for Multi-Party Computation.
In simple terms, it means:
A private key is never stored in one place
It is split into multiple cryptographic shares
No single system, server, or operator can sign alone
A valid signature only emerges when predefined parties and rules agree
This is the same class of technology used by institutional custodians and prime brokers, but implemented in a non-custodial, on-chain compatible way.
How Signing Works in Surf?
Step 1. User Creates a Smart Vault
When a user creates a vault:
The vault becomes the on-chain owner of funds
The user wallet is registered as the ultimate authority
The Guardian Layer rules are bound to the vault
Execution permissions are scoped to strategy contracts only
No hot wallet custody. No shared signing keys. No central operator control.
Step 2. AI Proposes an Action
The Surf Agent may propose actions such as:
Rebalancing between lending venues
Adjusting allocations
Moving liquidity
Closing or opening positions
At this stage, nothing is signed. This is only a proposal.
Step 3. Guardian Layer Authorisation
Before any signing happens:
The proposed action is checked against deterministic rules
Protocol allowlists are verified
Exposure caps are enforced
Slippage and liquidity thresholds are validated
Circuit breaker conditions are evaluated
If any invariant is violated:
The action is rejected
No signing process is triggered
No key material is engaged
Step 4. Vault-Scoped Signing via MPC
When an action is approved:
The vault triggers a signing request
The request is split across MPC nodes
Each node holds only a partial key share
The Guardian-approved execution payload is signed collaboratively
No node can reconstruct the private key
No node can sign arbitrary transactions
The resulting signature is:
Valid only for that specific transaction
Bound to the vault
Bound to the execution path
Bound to the approved parameters
Step 5. Atomic On-Chain Execution
The signed transaction:
Executes as a single atomic operation
Cannot be partially completed
Cannot be altered post-signing
Cannot be rerouted to other destinations
Funds move only:
Between allowlisted venues
Within the vault’s scope
Under the enforced rule set
Why This Matters
Most DeFi systems rely on one of two models:
Hot wallet operators Or fully autonomous smart contracts with upgrade keys
Both introduce hidden trust assumptions.
Surf’s model is different:
No single signing party
No operator discretion
No private key concentration
No backdoor execution path
No off-chain authority that can override rules
MPC ensures:
Key material is never exposed
Execution cannot be hijacked
Compromise of one node is insufficient
Signing is bound to deterministic policy
The Result
For the user, this means:
You keep ownership of your vault
You keep ultimate withdrawal authority
Automation cannot sign outside its mandate
No one can move funds without rule compliance
No one can reconstruct your private keys
No silent upgrades or hidden execution paths
This is how Surf allows AI to operate at scale, while cryptography guarantees that control and custody never leave the user.
Last updated