Key Delivery Message – encrypted XML file containing cryptographic keys required to decrypt and play a specific DCP on a specific cinema server, linking content access to authorized hardware and time windows.
What is a KDM?
A KDM (Key Delivery Message) is an encrypted XML file that contains the cryptographic keys to decrypt and play a DCP (Digital Cinema Package) on a specific cinema server. Without a valid KDM, the film cannot be played.
Basic Principle
| Aspect | Description |
|---|---|
| Purpose | Content decryption |
| Format | XML (encrypted) |
| Binding | Server-specific |
| Time Window | Period of validity |
Security Concept
| Element | Function |
|---|---|
| Encryption | AES-128 |
| Certificate | Server certificate |
| Unique Key | Per server |
| Time Lock | Start/End |
KDM Contents
| Information | Description |
|---|---|
| Content Key | Decryption key |
| Validity | Period of validity |
| Target | Server certificate |
| Content ID | DCP reference |
Workflow
| Step | Description |
|---|---|
| 1 | DCP created (encrypted) |
| 2 | Cinema certificate obtained |
| 3 | KDM generated |
| 4 | KDM delivered to cinema |
KDM Generation
| Element | Requirement |
|---|---|
| DKDM | Distribution Master Key |
| Certificate | From the target server |
| Time Window | Playback period |
| Software | KDM generator |
Server Certificates
| Component | Description |
|---|---|
| Public Key | For encryption |
| Server ID | Unique identifier |
| Chain | Certificate chain |
| Trusted | DCI-compliant |
Period of Validity
| Aspect | Typical |
|---|---|
| Start | Premiere date |
| End | Evaluation end |
| Flexibility | Daily precision |
| Extension | New KDM required |
KDM Types
| Type | Application |
|---|---|
| Feature | Main film |
| Trailer | Promotional content |
| Test | Technical check |
| Forensic | With watermark |
DKDM
| Aspect | Description |
|---|---|
| Distribution KDM | Master key |
| Function | Generate KDMs |
| Security | Strictly guarded |
| Issuance | From mastering |
Delivery Methods
| Method | Description |
|---|---|
| Standard | |
| Portal | Online systems |
| USB | Manual |
| Automated | TMS integration |
TMS Integration
| Function | Description |
|---|---|
| Theatre Management | Centralized management |
| Auto-Ingest | Automatic ingestion |
| Monitoring | Status monitoring |
| Alerts | Expiration warnings |
Common Problems
| Problem | Cause |
|---|---|
| Invalid Certificate | Incorrect certificate |
| Time Window | Outside validity period |
| Wrong Server | KDM for a different server |
| Corrupt File | Transmission error |
Troubleshooting
| Issue | Solution |
|---|---|
| Not playable | Check certificate |
| Expired | New KDM |
| Incorrect time | Check server clock |
| Unreadable | Re-transfer |
Time Zone Handling
| Aspect | Standard |
|---|---|
| UTC | Often used |
| Local | Some systems |
| Documentation | Important |
| Buffer | Schedule time buffer |
Distribution Services
| Provider | Service |
|---|---|
| Deluxe | KDM management |
| Cinedigm | Distribution |
| Arts Alliance | KDM delivery |
| DCM | Booking integration |
Costs
| Aspect | Factor |
|---|---|
| Per KDM | Usually minimal |
| Service | Distribution fee |
| Volume | Discounts possible |
| Rush | Surcharge |
Security Aspects
| Measure | Description |
|---|---|
| Encryption | 2048-bit RSA |
| Unique Keys | Per server/content |
| Audit Trail | Traceable |
| Revocation | Not possible |
Forensic Marking
| Function | Description |
|---|---|
| Watermark | In image/audio |
| Unique | Per cinema |
| Invisible | Not visible |
| Tracking | For piracy |
Standards
| Standard | Description |
|---|---|
| SMPTE | ST 430-1 |
| DCI | Compliance |
| Interop/SMPTE | Both formats |
| Certificate | X.509 |
Best Practices
| Practice | Reason |
|---|---|
| Early ordering | Time for QC |
| Certificate list | Keep up-to-date |
| Buffer time | Plan buffer time |
| Documentation | Track all KDMs |
Today
KDMs are the backbone of secure digital cinema distribution. Every DCP screening requires a valid, server-specific key. The system protects content rights and allows precise control over exhibition windows – essential for the modern film industry.