Understanding MPC Wallets for Agent Security

Multi-Party Computation wallets distribute key shares across parties, ensuring no single entity can move funds. Learn how this technology secures AI agent transactions at the cryptographic level.

The Problem with Traditional Wallets

Traditional cryptocurrency wallets rely on a single private key. If you have the key, you can move the funds. Full stop. This creates two problems for AI agents:

1. Single point of failure: If the agent's key is compromised, all funds are at risk
2. No spending controls: Whoever holds the key has unlimited authority -- there is no way to enforce policies at the cryptographic level

You could try to solve this with smart contracts, but that adds complexity and gas costs to every transaction. MPC offers a cleaner solution.

What is Multi-Party Computation?

Multi-Party Computation (MPC) is a cryptographic technique that allows multiple parties to jointly compute a function while keeping their inputs private. In the context of wallets, this means:

• The private key is split into multiple "shares"
• Each party holds one share
• To sign a transaction, parties collaborate without ever revealing their shares
• No single party ever has access to the complete private key

How Sardis Uses MPC

In Sardis, every agent wallet uses a 2-of-2 MPC scheme via Turnkey. Here is how the shares are distributed:

• Share 1: Your Agent -- Held locally by your agent or in your secure infrastructure. This share can initiate transactions but cannot complete them alone.
• Share 2: Sardis Policy Engine -- Held by Sardis. Will only co-sign transactions that pass your policy checks. Acts as a programmable guardian.

The Transaction Flow

When your agent wants to make a payment, here is what happens:

1. Agent requests payment: $50 to vendor.com
2. Agent's share creates partial signature
3. Request sent to Sardis Policy Engine
4. Policy Engine checks:
   - Amount under $100 limit
   - Vendor in allowlist
   - Daily limit not exceeded
5. Policy Engine co-signs with Share 2
6. Complete signature submitted to blockchain
7. Transaction confirmed

Security Properties

Non-Custodial

Sardis never has full control over your funds. We only hold one share of the key -- we cannot move funds without your agent's participation. This is fundamentally different from custodial solutions where a third party holds your keys.

Tamper-Proof Policy Enforcement

Because the policy engine controls a required key share, policies cannot be bypassed. Even if an agent is compromised or behaves unexpectedly, it cannot exceed the limits you have set.

No Single Point of Failure

If Sardis is compromised, attackers only get one key share -- insufficient to move funds. If your agent is compromised, same situation. Both parties would need to be compromised simultaneously.

Audit Trail

Every signing request is logged with full context: what the agent was trying to do, why it needed the funds, and whether the policy allowed it. This creates a complete audit trail for compliance and debugging.

Comparison with Alternatives

Technical Deep Dive: Threshold Signatures

Under the hood, Sardis uses threshold ECDSA signatures based on the GG20 protocol. Here is a simplified view of the math:

1. During wallet creation, a trusted dealer generates the private key and splits it into shares using Shamir's Secret Sharing
2. Shares are distributed to parties (in our case: your agent and Sardis)
3. During signing, parties engage in a multi-round protocol to produce a valid ECDSA signature
4. The resulting signature is indistinguishable from a normal single-key signature -- the blockchain never knows MPC was used

Key Rotation and Recovery

One advantage of MPC is easy key rotation. Without changing the wallet address, we can refresh the key shares. This allows:

• Regular rotation as a security best practice
• Rotation after suspected compromise
• Recovery if one party loses their share (through a secure recovery process)

Getting Started

Every Sardis wallet uses MPC by default -- no extra configuration needed. When you create a wallet through our SDK or dashboard, the MPC setup happens automatically. Your agent receives its key share, and you can start transacting immediately.