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Network security abandoned the trusted perimeter a decade ago. Every request is authenticated, every action is verified, nothing is trusted by virtue of its location. Commercial payments never made that shift. CAST is zero-trust architecture applied to the movement of value.

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The implicit-trust perimeter still exists in finance

Most payment controls assume that an instruction originating inside the organization — from a known email, an approved user, a familiar vendor record — is trustworthy. That is the perimeter model. Business Email Compromise is simply an attacker crossing the perimeter once and inheriting all the trust inside it.
Never trust, always verify — extended from packets to payments. No covered payment is trusted because of who submitted it. It is trusted only after the counterparty independently co-authors the terms through a cryptographically bound channel.

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Three zero-trust properties CAST inherits

Identity-bound action

WebAuthn ties each confirmation to a hardware-backed key — not a password, not an inbox an attacker can capture.

Least-privilege verification

The vendor sees only their own confirmation record. Buyer GL codes, budgets, and other vendors are never exposed across the counterparty surface.

Continuous validation

A bank-account change re-triggers the gate. Trust is not granted once and inherited forever — it is re-established at every covered event.

Separation of decision and execution

The actor that proposes a payment is never the sole authority that releases it.

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What the gap costs

Business Email Compromise alone accounts for roughly $2.9 billion in annual U.S. losses. The attack works by inserting a fraudulent instruction into a process that was never designed to verify the other party before payment. Zero-trust closes that exact gap: the bilateral confirmation is the verification step the payment perimeter never had.