VESPER - Verifiable STI Presentation and Evidence for RTU

This document defines VESPER (Verifiable STI Presentation and Evidence for RTU), a framework that extends the STIR architecture to cryptographically bind telephone number authority, domain identity, and originating provider authorization in a single delegate certificate. The delegate certificate is issued under the certificate policy defined under a STIR compliant eco-system and carries the assigned telephone numbers and authorized originating providers in a TNAuthList extension, the responsible entity's domain in a SubjectAltName, and an embedded Signed Certificate Timestamp (SCT) proving the certificate was recorded in a public transparency log prior to use. VESPER enables relying parties to verify that a telephone number was assigned to the entity whose domain is presented, and that calls from those numbers are originated by an authorized originating provider. The framework defines a certificate profile and issuance process grounded in existing STIR and ACME authority token mechanisms, a domain-hosted certificate repository with domain-controlled certificate discovery enabling cross-channel trust signals, a PASSporT usage profile for SIP signaling, and certificate transparency to support ecosystem auditability and detection of mis- issuance.