TSP100IV: CA Certificate upload appears to succeed but does not persist

[ZoeyJones]

Problem Summary

When configuring MQTTS (MQTT over TLS) on the TSP100IV printer, CA certificate uploads appear to succeed but the certificate does not persist after saving. This prevents using custom CA certificates for TLS verification.

Environment

• Printer Model: TSP100IV
• Connection Type: MQTTS (MQTT over TLS)
• Firmware: (latest available as of January 2025)

Steps to Reproduce

1. Generate a CA certificate (tested with both 2048-bit and 4096-bit RSA keys)
2. Access the printer's web configuration interface
3. Navigate to either:
   • CloudPRNT settings page, OR
   • SSL/TLS settings page
4. Upload the CA certificate
5. Interface shows "succeeded" message
6. Save settings
7. Return to the settings page - certificate is not saved

What We Tried

Approach	Result
4096-bit CA certificate	Upload shows success, but certificate not saved
2048-bit CA certificate	Upload shows success, but certificate not saved
Upload via CloudPRNT configuration page	Says "succeeded" but doesn't persist
Upload via SSL/TLS configuration page	Same result - doesn't persist

Expected Behavior

After uploading a CA certificate and saving settings, the certificate should persist and be used for TLS verification when connecting to MQTT brokers.

Actual Behavior

The web interface indicates the upload succeeded, but upon returning to the settings page or rebooting the printer, the certificate is not present.

Current Workaround

We are currently using the "Accept all" certificate validation option. While this still provides:

• ✅ TLS encryption (all traffic is encrypted)
• ✅ Authentication (username/password required for MQTT)

It does mean:

• ⚠️ No certificate validation (theoretical MITM risk)

Questions

1. Is there a specific certificate format requirement (PEM, DER, chain format)?
2. Are there file size limitations for the CA certificate?
3. Is there a known issue with certificate persistence on TSP100IV?
4. Are there specific firmware versions that address this?

Additional Context

This issue was encountered while setting up the printer to connect to a self-hosted MQTT broker with self-signed certificates. We would prefer to use proper certificate validation rather than "Accept all" for production deployments.

Any guidance on successfully uploading and persisting CA certificates would be appreciated.

[SMJ-Asuka]

The CA certificate format appears to be the root cause. Here are the responses to your questions:

1. PEM format
2. Status: Under investigation; please allow me a moment to confirm.
3. There are no known issues with the certificate.
4. This is the first report of this issue, so, unfortunately, there aren’t any specific firmware versions addressing it yet. Note that MQTT support starts from firmware version 2.2 and later.

[SMJ-Asuka]

For Question 2, the CA certificate upload has size limits per file and total count:

• Maximum size per file: 4 KB
• Maximum number of files: 15 certificates can be registered