Overview
ISO 26430-3:2008 - "Digital cinema (D-cinema) operations - Part 3: Generic extra-theater message format" specifies a secure, generic XML-based message wrapper called the Extra-Theatre Message (ETM) for use over unidirectional channels in D‑cinema security communications. Developed from SMPTE 430-3-2008 and aligned with W3C XML security primitives, the ETM defines a three-part message structure (authenticated public data, authenticated private/encrypted data, and signature/trust information) that can be extended for application-specific needs such as Key Delivery Messages (KDMs).
Key topics and technical requirements
- XML-based wrapper: ETM uses W3C Extensible Markup Language to represent payloads and extensions (see normative XML Schema included in the standard).
- Three-segment structure:
- AuthenticatedPublic - header fields, message identifiers, signer identity and optional extension elements that are readable by any recipient.
- AuthenticatedPrivate - encrypted blocks (EncryptedKey using RSA and optional EncryptedData using symmetric encryption) intended only for specified recipients.
- Signature/Trust - XML Signature elements that authenticate the ETM and include KeyInfo certificate chain details.
- Security primitives: The ETM relies on standard XML Encryption and XML Signature primitives and references established crypto standards (e.g., RSA, AES, SHA family, HMAC) as normative references for interoperability.
- Extensibility: Fields such as RequiredExtensions and NonCriticalExtensions allow vendors and applications to add structured, interoperable metadata without breaking baseline security.
- Unidirectional channel focus: Designed specifically for producer→distributor→exhibitor flows where messages are pushed and return channels are unavailable or constrained.
Applications and who uses it
- Key use cases:
- Distributing KDMs (Key Delivery Messages) to exhibitors’ projection systems.
- Sending security-related commands, annotations, or rights information from Distributors or Studios to Exhibitors.
- Any extra-theater security messaging where integrity, provenance and selective confidentiality are required over one-way links.
- Primary users:
- Theater Management System (TMS) developers and integrators
- Digital cinema security engineers and architects
- Content distributors, studios, and exhibitors implementing secure delivery chains
- Vendors of link encrypters/decrypters and media decrypters (SE, LE, LD, MD)
Related standards
- ISO 26430 (other parts): Part 1 (Key delivery message), Part 2 (Digital certificate)
- SMPTE 430 series (origin of ETM)
- W3C XML Encryption and XML Signature
- Cryptography references: FIPS-197 (AES), PKCS#1 (RSA), FIPS-180 (SHA)
ISO 26430-3:2008 provides a portable, interoperable foundation for secure D‑cinema message exchange, emphasizing XML security, extensibility, and compatibility with established cryptographic standards.
Open preview (PDF)Digital cinema (D-cinema) operations — Part 3: Generic extra-theater message format
