Protocol

Visa TAP

Trusted Agent Protocol

When the agent lists an lcp-hash field holding the ATR hash among the components it signs, its payer signature covers the ATR hash. Source: lcp docs: agentic checkouts⁠ (opens in a new tab) The Agentic Transaction Record (ATR) is one record of exactly what was agreed, for one transaction. Its ATR hash, the ATR’s fingerprint, is the proof bound to the transaction: change one byte of the ATR and it no longer matches. Source: lcp docs: the ATR⁠ (opens in a new tab) · Source: lcp docs: the ATR hash⁠ (opens in a new tab)

The Trusted Agent Protocol is a Visa project. Source: LCP §13⁠ (opens in a new tab) Integra is not affiliated; we read their published interfaces.

lcp docs: agentic checkouts⁠ (opens in a new tab) · lcp docs: the ATR⁠ (opens in a new tab) · lcp docs: the ATR hash⁠ (opens in a new tab) · LCP §13⁠ (opens in a new tab)

The protocol’s own site⁠The standard’s illustration of this protocol (LCP §C.6)⁠

Visa TAP

Agent recognition on card networks

The agent’s payer signature: Covers an lcp-hash field holding the ATR hash, when the agent lists that field among what it signs.

What it is

The Trusted Agent Protocol is a framework for agent-initiated transactions on HTTP Message Signatures (RFC 9421), with signatures establishing the agent’s identity, the consumer’s identity and the payment authorization. Source: LCP §C.6⁠ (opens in a new tab)

LCP §C.6⁠ (opens in a new tab)

Where the ATR hash rides

When the agent adds the ATR hash to what it signs, the signature it sends with the payment covers it.

Exhibit Where it rides, in the protocol’s and the package’s terms

The standard

TAP’s own covered components are the request’s authority and path, so a field outside them is unbound: to bind the ATR hash, the agent adds the field to the covered components, an extension TAP does not define. Source: LCP §C.6⁠ (opens in a new tab)

The package

The agent sends the ATR hash in an lcp-hash field and lists that field among the covered components of every agent-payer-auth signature it sends, so the payer signature the seller verifies covers it. Source: lcp docs: agentic checkouts⁠ (opens in a new tab)

The package classes this placement as a protocol extension (LCP §8.3.6): TAP publishes no extension registry, so covering the field is an arrangement between the agent and the seller rather than a filing. Source: LCP §C.6⁠ (opens in a new tab) · Source: lcp docs: pairings reference⁠ (opens in a new tab)

The card authorization itself does not carry the ATR hash. Source: lcp docs: pairings reference⁠ (opens in a new tab)

What a payment through it proves

Each pairing’s record states what a payment through it shows, and what it does not, in the package’s own words. These are read from the package when the site is built. Source: lcp docs: pairings reference⁠ (opens in a new tab)

On this pairing, the buyer’s signature covers the ATR hash, the payment does not leave a public proof of it, and no one can read it back from the chain alone. Source: lcp docs: pairings reference⁠ (opens in a new tab)

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

lcp docs: pairings reference⁠ (opens in a new tab)

Exhibit Each pairing’s record

The package

Pattern: Protocol Extension (LCP §8.3.6)⁠ (opens in a new tab)
What a payment through it proves: Before this payment, the buyer signed and paid an agreement transaction carrying this ATR's hash on <network>, recorded in <transaction>. The buyer's agent sent this ATR's hash in the lcp-hash field and listed that field among the covered components of every TAP agent-payer-auth message signature in the request. The seller checked that listing and did not verify a signature here, which belongs to its TAP recognition step. The card authorization itself does not carry the hash. This does not show that amount, payee or timing match the ATR's content.
LCP profile: card/visa-tap⁠ (opens in a new tab)

Where a sentence names <network> and <transaction>, the pairing’s record fills them in: they name the agreement payment the buyer made first. Source: lcp docs: pairings reference⁠ (opens in a new tab) · Source: lcp docs: the agreement URL⁠ (opens in a new tab)

The rails it settles on

Card networks

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