That is correct and s3 are in 3 different regions with object lifetime of maximum 10 days, it is backed by s3, the idea is to have the simplest code for anyone to review what it does (encrypt in browser and send encrypted blob to s3, key never leave browser)
This was my half day covid project to share file... inspired by firefoxsend a while back...
https://www.relaysecret.com/
the infra is super lightweight and you can deploy yourself with aws account, it costed me nothing to run and quite useful when needed :)