# Tempo · Integra

> On Tempo, MPP’s attribution memo and channel salts carry values derived from the ATR hash.

URL: https://integraledger.com/rails/tempo

Payment rail

## Tempo

On Tempo, MPP’s attribution memo and channel salts carry values derived from the ATR hash. [Source: lcp docs: rails⁠ (opens in a new tab)](https://github.com/IntegraLedger/integra-protocol/blob/66274bf/docs/guides/rails.md)

**Sources (1)**

[lcp docs: rails⁠ (opens in a new tab)](https://github.com/IntegraLedger/integra-protocol/blob/66274bf/docs/guides/rails.md)

### Where the ATR hash rides

On this rail, the ATR hash rides in MPP’s attribution memo.

#### The standard

A memo charge binds the ATR hash through 7 bytes only: whoever assembles the ATR could construct a second one sharing them, and the pairing’s own record says so. [Source: lcp docs: rails⁠ (opens in a new tab)](https://github.com/IntegraLedger/integra-protocol/blob/66274bf/docs/guides/rails.md)

- MPP’s attribution memo on `transferWithMemo`, whose last 7 bytes derive from the challenge id. [Source: lcp docs: rails⁠ (opens in a new tab)](https://github.com/IntegraLedger/integra-protocol/blob/66274bf/docs/guides/rails.md)

  `mpp/charge/tempo/memo` `mpp/charge/tempo/push`
- The channel’s salt, or the key authorization’s witness. [Source: lcp docs: rails⁠ (opens in a new tab)](https://github.com/IntegraLedger/integra-protocol/blob/66274bf/docs/guides/rails.md)

  `mpp/session/tempo` `mpp/subscription/tempo`

Entry points: `@integraledger/lcp/tempo` , `@integraledger/lcp/mpp`

#### The data

Read from the published packages when the site was built; nothing here is typed by hand.

The ATR hash of the site’s example ATR, as this rail carries it

the MPP challenge id that carries H, from which the memo’s last 7 bytes derive

hEjcG3FqUQMofLjzXja2FP_ZHmMKuLeRGDPFR0itXKY.0

Computed from the site’s example ATR by this rail’s own helper in the package, when the site was built.

### What a payment on this rail proves

Of these 4 pairings, 2 have the buyer’s signature cover the ATR hash, 4 leave a public proof of it, and 1 let anyone read it back from the chain alone. [Source: lcp docs: pairings reference⁠ (opens in a new tab)](https://github.com/IntegraLedger/integra-protocol/blob/66274bf/docs/reference/pairings.md)

Switch to Technical to see each pairing, and the sentence its record states about what a payment through it proves.

#### The standard

- **`mpp/charge/tempo/memo` Opaque Challenge Buyer signs H: no H on chain: no Public proof: yes Recoverable from chain: no**

  Pattern: [Opaque Challenge (LCP §8.3.4)⁠ (opens in a new tab)](https://github.com/legal-context-protocol/legal-context-protocol/blob/c8df26d/spec/legal-context-protocol-v1.md#834-opaque-challenge-parameter)

  Where the ATR hash rides: MPP’s attribution memo on `transferWithMemo`, whose last 7 bytes derive from the challenge id.

  What a payment through it proves: The ATR's hash is in the MPP challenge this payment answered: its id is the hash in base64url with the challenge's position, protected by the server's binding of the challenge. The payer signed a Tempo transaction whose transferWithMemo call carries MPP's attribution memo, whose 7-byte nonce is keccak256 of that id. The chain verified the signature when it executed the call, and the memo is on chain as the memo topic of the token's TransferWithMemo event. It ties the payment to the challenge instance, and binds this ATR's hash only through those 7 bytes: whoever assembles the ATR can construct a second ATR whose challenge id gives the same 7 bytes. This does not show that amount, payee, asset or timing match the ATR's content.
- **`mpp/charge/tempo/push` Opaque Challenge Buyer signs H: no H on chain: no Public proof: yes Recoverable from chain: no**

  Pattern: [Opaque Challenge (LCP §8.3.4)⁠ (opens in a new tab)](https://github.com/legal-context-protocol/legal-context-protocol/blob/c8df26d/spec/legal-context-protocol-v1.md#834-opaque-challenge-parameter)

  Where the ATR hash rides: MPP’s attribution memo on `transferWithMemo`, whose last 7 bytes derive from the challenge id.

  What a payment through it proves: The ATR's hash is in the MPP challenge this payment answered: its id is the hash in base64url with the challenge's position, protected by the server's binding of the challenge. The payer signed and broadcast a Tempo transaction whose transferWithMemo call carries MPP's attribution memo, whose 7-byte nonce is keccak256 of that id. The chain verified the signature when it executed the call, and the memo is on chain as the memo topic of the token's TransferWithMemo event, read after the money had moved. It ties the payment to the challenge instance, and binds this ATR's hash only through those 7 bytes: whoever assembles the ATR can construct a second ATR whose challenge id gives the same 7 bytes. This does not show that amount, payee, asset or timing match the ATR's content.
- **`mpp/session/tempo` Native Field Buyer signs H: yes H on chain: yes Public proof: yes Recoverable from chain: no**

  Pattern: [Native Field (LCP §8.3.1)⁠ (opens in a new tab)](https://github.com/legal-context-protocol/legal-context-protocol/blob/c8df26d/spec/legal-context-protocol-v1.md#831-native-field)

  Where the ATR hash rides: The channel’s salt, or the key authorization’s witness.

  What a payment through it proves: The ATR's hash is in the MPP session challenge this channel opened under: its id is the hash in base64url with the challenge's position. The payer signed a Tempo transaction whose one call to the channel escrow opens a channel with this ATR's hash as its salt, and the chain verified that signature when it executed the call. The escrow's ChannelOpened event names the channel, whose id commits to the salt; on the TIP-1034 escrow the event also carries the salt itself. This does not show that amount, payee, asset or timing match the ATR's content. Later requests in this channel were paid under this ATR by vouchers the seller did not meter; each voucher signs a commitment to this ATR's hash.

  LCP profile: [mpp/session/evm-tempo⁠ (opens in a new tab)](https://github.com/IntegraLedger/integra-protocol/blob/66274bf/lcp/profiles/mpp-session-evm-tempo.md)
- **`mpp/subscription/tempo` Native Field Buyer signs H: yes H on chain: yes Public proof: yes Recoverable from chain: yes**

  Pattern: [Native Field (LCP §8.3.1)⁠ (opens in a new tab)](https://github.com/legal-context-protocol/legal-context-protocol/blob/c8df26d/spec/legal-context-protocol-v1.md#831-native-field)

  Where the ATR hash rides: The channel’s salt, or the key authorization’s witness.

  What a payment through it proves: The ATR's hash is the MPP subscription challenge's id, in base64url. The payer's root key signed a Tempo key authorization whose witness is this ATR's hash, granting the seller's access key a per-period limit. The chain verified that signature when the activation transaction registered the key, and the account keychain's KeyAuthorizationWitness event carries the payer's account and this hash as topics. The same transaction transferred the first period's payment to the recipient. This does not show that amount, period, payee, asset or timing match the ATR's content. Later billing periods were paid under this ATR by renewal transfers the seller did not read.

### Reading the settlement

The package reads a payment’s settlement through a reader you supply: the endpoint, the credentials, the timeouts and the retries are yours. A reader that fails never makes a payment read as failed. [Source: lcp docs: reading settlement⁠ (opens in a new tab)](https://github.com/IntegraLedger/integra-protocol/blob/66274bf/docs/guides/rails.md#reading-settlement)

**Sources (1)**

[lcp docs: reading settlement⁠ (opens in a new tab)](https://github.com/IntegraLedger/integra-protocol/blob/66274bf/docs/guides/rails.md#reading-settlement)

#### The standard

**Reader**

`EvmReader`

**Its calls**

`eth_getTransactionReceipt`, `eth_getBlockByNumber` for the `safe` and `finalized` marks, `eth_getTransactionByHash`, `eth_call` at a block number

**A settled read carries**

the finality mark reached: `latest`, `safe` or `finalized` [Source: lcp docs: reading settlement⁠ (opens in a new tab)](https://github.com/IntegraLedger/integra-protocol/blob/66274bf/docs/guides/rails.md#reading-settlement)

### The protocols that pay on it

- [MPP](https://integraledger.com/protocols/mpp)

[lcp docs: rails⁠ (opens in a new tab)](https://github.com/IntegraLedger/integra-protocol/blob/66274bf/docs/guides/rails.md)