Il Sistema di Interscambio, or SdI, is the official Italian gateway that receives, checks, and routes electronic invoices in the public-administration workflow. In practice, it acts as a controlled message broker between suppliers and public entities, verifying format and required data before forwarding the document or returning an acceptance or rejection notice.
From a cyber-security perspective, SdI is important because it sits at a trust boundary. If invoice messages, receipts, or status codes are altered, misrouted, or forged, organizations can lose integrity in their accounting and audit records even without malware. Defenders therefore treat SdI traffic as sensitive business data: they preserve transmission logs, validate signatures and receipts, correlate each invoice with its outcome, and monitor for abnormal rejections, resubmissions, or duplicate records. Good controls around SdI help prove what was sent, what was accepted, and what must be corrected.