I tried to build a “trustless” file sharing app (browser-only)

I tried to build a “trustless” file sharing app (browser-only)

I build Figma plugins, but recently I ran into a problem:

I needed to share files (PDF / PPT / assets),
and I realized I don’t actually trust any file sharing service.

Not because they’re bad — but because:

they can technically read your files.

So I tried something different

I’m building a file sharing flow where:

everything happens in the browser
files are encrypted before upload
server stores only opaque blobs
the decryption key is in the URL (#key=...)

Meaning:

if you don’t have the link, you literally can’t read the file
even I (the developer) can’t access it

The interesting parts

1. Client-side processing is painful

Users upload anything:

PDF / PPT / Word / images

Trying to normalize formats inside the browser is way harder than expected
(WASM helps, but still messy)

1. Encryption is the easy part

Web Crypto API works great.

The real issues are:

large files (100MB+)
memory spikes
blocking UI

→ solution: chunking + Web Workers

1. UX is the hardest problem

Users don’t care about encryption.

They want:

drag & drop
click “create link”
done

Making something secure feel this simple is the real challenge.

Why I’m sharing this

I’m starting to think:

“trustless apps” might be a real category

Where you don’t need to trust:

the platform
the backend
even the developer

Curious if anyone here has built:

browser-only file processing
large file encryption pipelines
WASM-heavy apps

Would love to hear how you handled performance.