Settle Payments on Tempo

Tempo is a stablecoin-native settlement chain co-designed by Stripe. Tenzro's tempo-bridge feature lets nodes participate directly — signing EIP-155 Secp256k1 transactions via k256, submitting eth_sendRawTransactioncalls, and querying balances — to settle MPP/x402 payments on Tempo rather than (or in addition to) the Tenzro Ledger.

Flow Diagram

Tempo settlement flow (server-side, HTTP 402)

 client                          resource server                  Tempo chain
 ------                          ---------------                  -----------
    │                                   │                                │
    │  GET /inference (no auth)         │                                │
    ├──────────────────────────────────►│                                │
    │                                   │                                │
    │   402 Payment Required            │                                │
    │◄──────────────────────────────────┤                                │
    │   challenge: { rail: "tempo",     │                                │
    │                amount: "0.01",    │                                │
    │                token:  "USDC",    │                                │
    │                payee:  "0x..." }  │                                │
    │                                   │                                │
    │  sign + submit tempo tx           │                                │
    ├────────────────────────────────────────────────────────────────────►
    │                                   │                                │
    │                                   │       confirmed (1 block)      │
    │                                   │◄───────────────────────────────┤
    │                                   │                                │
    │   retry + X-PAYMENT-TX header     │                                │
    ├──────────────────────────────────►│                                │
    │                                   │                                │
    │                                   │  verify inclusion via RPC      │
    │                                   ├────────────────────────────────►
    │                                   │         proof                  │
    │                                   │◄───────────────────────────────┤
    │   200 OK + X-PAYMENT-RECEIPT      │                                │
    │◄──────────────────────────────────┤                                │

Step 1: Configure a Participant

// tempo.toml — or inline TempoConfig
[tempo]
rpc_url           = "https://rpc.tempo.example"
chain_id          = 7338
participant_id    = "did:tenzro:machine:c3d4..."
default_stablecoin = "USDC"
signing_key       = "secp256k1:..."     // or provision via MPC wallet

use tenzro_payments::tempo::{TempoConfig, TempoParticipant};

let cfg = TempoConfig::from_toml("tempo.toml")?;
let participant = TempoParticipant::new(cfg).await?;

// Query balance on Tempo
let bal = participant.balance_of("USDC", "0xWalletOnTempo...").await?;
println!("{} USDC", bal);

Step 2: Direct TIP-20 Transfer

TempoParticipant::transfer implements the full EIP-155 signing pipeline:

• Build EIP-1559 transaction (max_fee_per_gas, max_priority_fee_per_gas, gas limit, nonce)
• RLP-encode the unsigned transaction
• Take keccak256 digest
• Sign with the participant's secp256k1 key via k256
• Serialize with v = recId + 35 + 2 * chainId
• Submit via eth_sendRawTransaction and poll for inclusion

// Sign and submit a TIP-20 transfer — full EIP-155 pipeline under the hood:
//   * Construct EIP-1559 tx
//   * RLP encode
//   * Keccak-256 digest
//   * Secp256k1 sign via k256
//   * Serialize with v = recId + 35 + (2 * chainId)
//   * eth_sendRawTransaction to the Tempo RPC

let receipt = participant.transfer(
    "USDC",                           // TIP-20 token symbol
    "0xRecipientOnTempo...",
    "10.50",                          // decimal string
).await?;

println!("tx:    {}", receipt.tx_hash);
println!("block: {}", receipt.block_number);
println!("status: {}", receipt.status);  // Success | Reverted

Step 3: Settle MPP over Tempo

This is the core production use case — the same MPP credential that your HTTP middleware already verifies can be settled on Tempo instead of the Tenzro Ledger. The MPP receipt simply references the Tempo tx hash:

// MPP credential settled through Tempo
use tenzro_payments::{MppPaymentServer, PaymentProtocol};

let mpp      = MppPaymentServer::new(/* ... */);
let tempo    = TempoParticipant::new(cfg).await?;

// 1. Client presents MPP credential
let credential = request.headers()
    .get("X-PAYMENT-MPP")
    .ok_or("missing credential")?;

// 2. Verify signature + session state
let verified = mpp.verify_credential(credential).await?;

// 3. Settle on Tempo in the background
let tempo_settlement = tempo.transfer(
    &verified.stablecoin,
    &verified.payee_wallet,
    &verified.amount,
).await?;

// 4. Return MPP receipt referencing the Tempo tx hash
let receipt = mpp.issue_receipt(&verified, tempo_settlement.tx_hash)?;

Step 4: Tempo ↔ Tenzro Bridging

// Cross-chain Tempo ↔ Tenzro settlement via TempoBridgeAdapter
use tenzro_payments::tempo::TempoBridgeAdapter;

let bridge = TempoBridgeAdapter::new(tempo_cfg, tenzro_rpc).await?;

// Deposit: move USDC from Tenzro to Tempo
let deposit_tx = bridge.deposit_to_tempo(
    "USDC",
    "100.0",
    "did:tenzro:machine:c3d4...",
).await?;

// Withdraw: pull USDC settled on Tempo back to Tenzro
let withdraw_tx = bridge.withdraw_to_tenzro(
    "USDC",
    "50.0",
).await?;

Step 5: CLI

# Register as a Tempo participant (provisions MPC wallet for Tempo chain)
tenzro payment tempo register \
  --stablecoin USDC \
  --rpc-url https://rpc.tempo.example

# Check a Tempo balance
tenzro payment tempo balance --token USDC --address 0xWalletOnTempo...

# Direct transfer
tenzro payment tempo transfer \
  --token USDC \
  --to 0xRecipientOnTempo... \
  --amount 10.50

# Settle an outstanding MPP session through Tempo
tenzro payment settle \
  --session-id mpp-sess-01HR... \
  --rail tempo

What You Learned

• EIP-155 pipeline — RLP + keccak + secp256k1 + v = recId + 35 + 2 * chainId
• TempoParticipant — balance queries, direct transfers, receipt polling
• MPP → Tempo — settle HTTP 402 credentials on the Tempo chain
• Bridge adapter — move stablecoin balances between Tenzro and Tempo