Building Proof of Work for Developers: How I Used Hash Chaining to Make Skill Verification Tamper-Proof

Brayan Tematio — Thu, 23 Jul 2026 08:41:26 +0000

Building Proof of Work for Developers: How I Used Hash Chaining to Make Skill Verification Tamper-Proof

The problem

Anyone can write "Expert in Python" on a resume. Recruiters know this,
which is why technical interviews exist — but they're slow, expensive,
and don't scale, especially in markets where trust signals (LinkedIn
endorsements, GitHub stars, alumni networks) are thinner than in the
US/EU tech hubs.

I'm building Hokay, a platform for French-speaking African developers,
around a different idea: instead of claiming skills, you prove them —
and that proof is cryptographically verifiable, not just a badge someone
could have faked or bought.

The core mechanic: hash chaining

Every time a developer solves a challenge on Hokay, their submission
gets recorded as a snapshot. Every few minutes, snapshots get chained
together using SHA-256 — each new hash includes the previous one, the
same principle blockchains use for tamper-evidence, minus the
distributed consensus overhead (I don't need a blockchain, I need
verifiability).

The result: if anyone — including me, as the platform owner — tried to
retroactively edit someone's history (inflate a score, backdate a
submission), the hash chain breaks and it's detectable. Every developer
gets a public certificate they can share, and anyone can verify it
wasn't tampered with.

The stack

Django + Django REST Framework for the API
Django Channels + Daphne for real-time features (chat, live challenge status)
Celery + Redis for async processing (challenge evaluation, notifications, snapshotting)
PostgreSQL as the source of truth
Firebase Cloud Messaging for push notifications
A custom code evaluator supporting 18+ languages, sandboxed with firejail, with AI-assisted scoring (Groq) for challenges that aren't pure input/output matching

What I learned building this solo

The hard part isn't the crypto, it's the plumbing. Hash chaining
itself is maybe 100 lines of code. Making sure every notification
path actually fires (push notifications on Android turned out to
have three separate silent-failure modes — I wrote about debugging
that separately) took a full evening of systematic debugging.
Trust infrastructure is worthless without users. I can build
the most cryptographically sound verification system in the world —
if nobody's solving challenges, there's nothing to verify. Retention
is now my only real metric that matters.
Building for an underserved market means building the whole
stack yourself. There's no local Stripe-equivalent trust
infrastructure, no established dev-certification culture to plug
into — you're building the primitives, not just the app.

What's next

Hokay is free and live at hokay.site. I'd love
feedback from other developers — especially anyone who's tackled
skill-verification or reputation systems before. What would make you
trust a platform's "proof" claim?

DEV Community: Brayan Tematio

Building Proof of Work for Developers: How I Used Hash Chaining to Make Skill Verification Tamper-Proof

Building Proof of Work for Developers: How I Used Hash Chaining to Make Skill Verification Tamper-Proof

The problem

The core mechanic: hash chaining

The stack

What I learned building this solo

What's next