FideX Application Statement 5 (AS5) Protocol

This document specifies the FideX Protocol (AS5), a modern application-layer protocol for secure Business-to-Business (B2B) message exchange. FideX provides cryptographic non-repudiation, data integrity, and confidentiality using JOSE (JSON Object Signing and Encryption) over HTTPS, replacing legacy AS2 and AS4 standards with a REST-oriented approach accessible to modern web developers. FideX adopts the "AS" naming lineage: AS2 ([RFC4130]) used S/MIME over HTTP; AS4 ([OASIS-ebMS]) used SOAP/WS-Security; AS5 (FideX) uses REST/JSON/JOSE over HTTPS. This document defines the message format, cryptographic operations, partner discovery, state management, acknowledgment receipts (J-MDN), and error handling.