# certs/

## bambu_ca2.pem

Bambu Lab's shared root CA ("BBL CA2 RSA") used to verify a printer's LAN-mode
MQTTS (port 8883) certificate. Current-generation Bambu printers present a
certificate signed by (a chain rooted at) this CA - trust this one file
instead of fetching/pinning a certificate per printer.

- Source: https://github.com/bambulab/BambuStudio/blob/master/resources/cert/printer.cer
- Fetched: 2026-08-28
- SHA-256 fingerprint: `E9:8F:19:57:8B:3F:12:4A:CE:6B:8A:24:7F:FE:DA:52:DC:99:C8:9F:D4:E7:D2:0C:82:82:99:77:B7:F3:35:02`
- Verified with `openssl x509 -noout -text`: self-signed (`Issuer == Subject`),
  `Basic Constraints: CA:TRUE`, `Key Usage: Certificate Sign, CRL Sign` - a
  genuine root CA, not a per-device leaf certificate. Valid until 2050.

The "CA2" name implies there was a CA1 generation before it, and at least
one current model - P1P - doesn't chain to this root either: BambuStudio's
`resources/cert/` only has this one file (plus an unrelated
`*.bambulab.com` leaf cert for their cloud API), so there's no second
bundled file to grab for P1P. That means it's a genuine per-device
certificate, the same "download it from the printer" case as the older
units. `CONTINUUM_BAMBU_CA_CERT_OVERRIDES` (see `.env.example`) is a
per-printer-id map for exactly this - there's no single fleet-wide
override, because different printers can legitimately need different
certificates at the same time.

If a printer's connection ever fails certificate verification against this
file, re-fetch from the source URL above (BambuStudio ships whatever the
current fleet needs) and update the fingerprint here.

## `pinned/`

Not checked in (gitignored) - where `BambuPrinter::ensure_trusted` saves a
certificate it auto-pinned via trust-on-first-connect, one file per
printer, named `<serial number>.pem`. This only happens for a printer
whose certificate doesn't verify against `bambu_ca2.pem` above (P1P, at
least) and that doesn't already have an explicit `ca_cert_path` set in
`printers.toml` - see that method's doc comment in `src/printer/bambu.rs`
for the full trust-on-first-connect flow, and the SSH-host-key analogy it's
built on. Delete a printer's file here to force it to re-pin (a real
error, not silent, if the certificate it captures the second time still
doesn't verify) the next time it connects.