On the agent side, KYH passes the human’s device identifier and IP address to the merchant through a small number of additional HTTP headers. Agents can bind device data to a session in one of two ways. At the same time, they can embed Sardine’s SDK in their own app, which captures the device fingerprint and ties it to a session key, or they can request a Method URL from a merchant that supports the protocol and load it in the background on the customer’s device. At checkout, the merchant uses Sardine to retrieve the associated device and IP signals and verify the human behind the order. Sardine has implemented KYH in its own Personal Agent. On the merchant side, the protocol supports step-up verification for agentic transactions. When Sardine’s Device Intelligence solution detects that a checkout was completed via an agent such as Muse, Dot or Instinct, the merchant can send the customer an SMS containing a verification link. Opening the link allows Sardine to fingerprint the customer’s browser and connect it to the cloud browser fingerprint used by the agent. Each link can be opened up to three times and expires five minutes after creation, with a new link available for the same session if required.