Security

How the connection is protected

Your desktop generates its own certificate and shows you its fingerprint in the pairing code. Your phone accepts that key and no other.

This is stronger than ordinary HTTPS, not weaker. Normal web encryption trusts roughly 150 certificate authorities, any of which could vouch for an impostor. Hopli trusts exactly one key, and it reached your phone through your own camera.

Why you compare numbers

Someone who photographs your pairing code holds the same certificate fingerprint and the same token you do. They could reach your desktop.

So both devices generate a random value and combine them into eight digits unique to that connection. An impostor's screen shows different digits than the phone in your hand. If they don't match, deny it — that mismatch is the whole point.

Digits rather than pictures because emoji are drawn differently on Windows, Android and iPhone, which would make honest pairs look like mismatches.

Nothing moves without you

Every file is announced before it is sent. Nothing is written to either device until the receiving side agrees, and a prompt left unanswered is treated as no — silence is never consent.

Every completed transfer is checksummed on both ends. A file that arrives altered is discarded rather than saved, so a corrupted transfer cannot sit in your folder looking fine.

What Hopli does not protect against

Being honest about the limits, because a security page that only lists strengths is marketing.

This website could be tampered with. Hopli's phone side is a web page. Whoever controls the host serving it could serve different code — and that code would be doing your encrypting. Your browser caches the page after the first visit, which limits this to a single moment of trust rather than an ongoing one, but it does not remove it. Every browser-based encrypted product has this property; most do not mention it.

A compromised device. If something malicious is already running on your phone or desktop, it can read your files directly. No transfer tool can fix that.

Approving without looking. The prompts only work if you read them. Hopli tries to keep them rare so they stay meaningful.

Reporting a problem

If you find a vulnerability, please report it privately before publishing, and give a reasonable window for a fix. Serious findings are welcome; the full threat model lives with the source and goes into more detail than this page.