xMicroPay: Autonomous Agent Payment Authorization

The Problem

Autonomous AI agents are making purchasing decisions, but giving agents unrestricted payment authority creates unacceptable financial risk.

Agentic commerce is projected to reach $50B, but organizations have no cryptographic way to limit agent spending. Policy-based controls are bypassable. Shared payment credentials mean one compromised agent can drain accounts.

Manual human-in-the-loop approval for every transaction defeats the purpose of autonomous agents. What’s needed is configurable threshold authorization: auto-approve small transactions, require multi-party approval for large ones.

The Old Way

The PRIVATE.ME Solution

xMicroPay provides threshold-controlled payment authorization where agents can autonomously approve transactions below configurable limits and escalate to multi-party approval above them.

Payment authorization tokens are XorIDA-split across designated approvers. Transactions below the threshold auto-approve with the agent’s DID signature. Transactions above require K-of-N approver signatures via xLock push-auth.

Every transaction is recorded in an HMAC-chained audit trail with amount, parties, approval chain, and timestamps. Spending limits are enforced cryptographically, not by policy.

The New Way

How It Works

xMicroPay combines DID identity, threshold authorization, and HMAC-chained audit to create a cryptographically enforced payment control layer for autonomous agents.

Payment Channel Architecture

xMicroPay implements bidirectional payment channels with XorIDA-split channel state. Payment channels enable instant, fee-free transactions between parties by minimizing settlement events.

Channel Setup: Two parties establish a channel by committing funds to a multi-signature wallet. The initial channel state (balance distribution) is XorIDA-split into K-of-N shares and distributed to designated custodians. Each party holds a threshold of shares enabling them to prove their balance without reconstructing the full state.

State Updates: Each micropayment updates the tentative balance distribution. Both parties sign the new state, which is split and distributed to custodians. No settlement occurs until channel close. Updates settle in under one second with sub-penny fees. State updates use Hashed Timelock Contracts (HTLCs) to ensure atomicity.

Multi-hop Routing: Payments can route through intermediary channels without requiring direct channels between sender and receiver. If Alice has a channel with Bob and Bob has one with Carol, Alice can pay Carol by routing through Bob. HTLCs ensure all-or-nothing settlement across the route. Atomic transfers reduce counterparty risk across intermediaries.

Channel Lifecycle

Open: Parties commit funds and establish initial XorIDA-split state. Dual-funded channels allow both parties to contribute capital, reducing blockchain footprint. Channel factories enable multiple users to share a single transaction for opening numerous channels, reducing costs by 90 percent for high-volume users.

Update: Off-chain state updates occur instantly. Each update is threshold-signed and HMAC-chained to the previous state. State channels support thousands of updates per second per channel.

Close/Settle: Either party can initiate channel closure. The final state is reconstructed from K-of-N shares, verified via HMAC chain, and settled. Time-locked refunds protect against unresponsive counterparties. Hierarchical channels enable flexible off-chain resizing without on-chain transactions.

Dispute Resolution

If parties disagree on channel state, the HMAC-chained audit trail provides tamper-evident evidence. The most recent mutually-signed state is considered authoritative. Time-locked refunds ensure funds are not held hostage by uncooperative parties. Penalization mechanisms discourage broadcasting stale states.

Use Cases

Integration

import { PaymentGate } from '@private.me/xmicropay';

const gate = await PaymentGate.create({
  agentDid: agent.did,
  autoApproveLimit: 100, // USD
  threshold: { approvers: 2, of: 3 }
});
const auth = await gate.authorize(txn);

Security Properties

Verifiable Data Protection

Every operation in this ACI produces a verifiable audit trail via xProve. HMAC-chained integrity proofs let auditors confirm that data was split, stored, and reconstructed correctly — without accessing the data itself.

Ready to deploy xMicroPay?

Talk to Ren, our AI sales engineer, or book a live demo with our team.

Ship Proofs, Not Source

xMicropay generates cryptographic proofs of correct execution without exposing proprietary algorithms. Verify integrity using zero-knowledge proofs — no source code required.

Use Cases