What is the AS4 messaging protocol used in Peppol?
AS4 (Applicability Statement 4) is a web service-based messaging standard for secure, reliable B2B document exchange. It is the mandated transport protocol for Peppol network document delivery between access points. AS4 provides message-level security (signing and encryption), reliable delivery with delivery receipts, non-repudiation of origin and receipt, and error handling. It is derived from the OASIS ebMS 3.0 specification and is part of the Peppol Transport Infrastructure specifications.
What security and reliability features does AS4 provide?
AS4 messaging security and reliability features: (1) Message signing - sender signs the message with their X.509 certificate; receiver verifies authenticity; (2) Message encryption - message content encrypted in transit; (3) Non-repudiation - signed receipt cannot be repudiated; sender has evidence of delivery; (4) Duplicate detection - AS4 message IDs prevent duplicate processing; (5) Error signaling - standardized error codes and notifications when delivery fails; (6) Reliable messaging - acknowledgement-based delivery confirmation.
Frequently Asked Questions
- Is AS4 only used in Peppol?
- AS4 is used beyond Peppol. The EU's CEF (Connecting Europe Facility) specifies AS4 as a standard for government document exchange. Various industry standards bodies use AS4 for B2B document exchange including in energy, banking, and healthcare. The European e-Justice portal uses AS4. In some countries, the national e-invoicing clearing platform uses AS4. AS4 is a general-purpose secure B2B messaging standard; Peppol has adopted it as its mandated transport layer.
- What is the difference between AS4 and AS2?
- AS2 (Applicability Statement 2) is an older standard widely used for EDI exchange over HTTPS. AS4 is its successor, modernized for SOAP-based web services and with improved security features. AS4 uses SOAP with attachments; AS2 uses MIME with HTTP. Both provide signing and encryption, but AS4 has more sophisticated security and reliability mechanisms. Peppol mandated the transition to AS4 from AS2 in 2021. Many companies still use AS2 for legacy EDI; AS4 is the standard for modern e-invoicing networks.