Authenticate as the service account given then use GCP KMS key with GCP Secrets manager encrypted blob to get flag:

Writeup: [https://ctf.rip/write-ups/cloud/downunderctf-lost-n-found/](https://ctf.rip/write-ups/cloud/downunderctf-lost-n-found/)

Original writeup (https://ctf.rip/write-ups/cloud/downunderctf-lost-n-found/).