How an AI agent pays on a user's behalf — without the platform ever holding funds or credentials.
A Universal Purchase Mandate is an Ed25519-signed authorization format that lets an AI agent initiate a transaction on a user's behalf — without Nexbid ever holding funds or card data. Merchants verify the mandate without any Nexbid-specific integration; the flow stops at the checkout.
62 machine-checked Lean 4 theorems (lake-build verified) prove the authorization invariants. No custodial risk, no delegated credentials — merchants verify the signed mandate independently.
It is an open, signed data format — not a wallet and not a payment service. The mandate describes what an agent may buy (product, budget cap, validity) and who authorized it. The agent presents the mandate to the merchant; the merchant checks the Ed25519 signature and runs its own checkout. Nexbid is never in the money flow.
Three layers (ADR-008). Layer 1 — OS-native biometric consent: the user authorizes per transaction via Face ID, Apple Pay, Google Pay, or Windows Hello; the biometrics never leave the device. Layer 2 — conditional merchant auth: if the user has a merchant account, an OAuth token sits in the device keychain; otherwise Stripe guest checkout with a pre-filled profile. Layer 3 — the Ed25519-signed Universal Purchase Mandate that merchants verify without any Nexbid integration.
By design. No custodial risk means no e-money license and no holding of third-party funds. No delegated credentials means no password or card sharing. Payment always happens at the merchant — Nexbid only supplies the authorization format. That lowers regulatory and liability risk and makes the mandate adoptable by any merchant.
Every merchant checks the Ed25519 signature independently — no Nexbid API in the critical path. The authorization invariants (only authorized amounts, only valid mandates, no reuse) are formally proven in Lean 4: 62 machine-checked theorems, lake-build verified. That is a higher assurance level than the "boring restrictions" assertion of other trust layers.
The format is crypto-agile. Today it signs with Ed25519; the migration path is hybrid Ed25519 + ML-DSA-65 (NIST FIPS 204), rolled out per signing surface (ADR-035). The algorithm identifier is an explicit slot in the format — not a hardcoded literal — so that 10-year audit trails stay protected against "harvest now, decrypt later".
The mandate is orthogonal to the transaction and runs ON the transaction rails. Interop is documented: AP2 (IntentMandate), UCP (checkout sessions), ACP, and x402 for crypto-native payment, A2A (Agent Cards) for identity. The mandate answers "what may the agent buy", not "who settles the payment" — co-existence, not competition.
Yes. The Universal Purchase Mandate is part of the AdCP standard (MIT-licensed). The Lean sources and the specification are public on GitHub at nexbid-dev/protocol-commerce (lake-build verified). The signed authorization infrastructure shares code with the compliance manifest (ADR-006).
An Ed25519-signed authorization format that lets an AI agent act on a user's behalf — without Nexbid ever holding funds or credentials. Merchants verify the mandate without any Nexbid-specific integration; the flow stops at the checkout, where a human or a pre-issued mandate confirms.
No. No custodial risk, no delegated credentials, no e-money license required. Payment happens at the merchant; Nexbid only supplies the signed authorization format. Biometric confirmation (Face ID, Windows Hello) never leaves the user's device.
Via the Ed25519 signature, which any merchant can check independently. The authorization invariants are formally proven in Lean 4 (62 machine-checked theorems, lake-build verified) and crypto-agile: Ed25519 today, hybrid Ed25519 + ML-DSA-65 as the post-quantum path per ADR-035.
ACP settles the transaction centrally (a fee flows to OpenAI). The Universal Purchase Mandate is an open, vendor-neutral authorization format (MIT) that runs ON UCP/ACP rails — the merchant keeps the checkout, no platform lock-in, no shared card data.
Yes. It is part of the AdCP standard (MIT-licensed) and interoperable with UCP, ACP, AP2, and x402. The Lean sources and the specification are public on GitHub (nexbid-dev/protocol-commerce, lake-build verified).