Proof of Work Captcha

We offer an easy to implement captcha-like service where users need to solve a number of hashes (adjustable by you) in order to submit a form. This prevents spam at an inconvenience that is comparable to a classic captcha. All with the added benefit of earning you money.

For an example, have a look at our signup page.

The captcha API is modeled after Google’s reCaptcha. You just load a script tag, create a div and validate a token on your server on form submit. See the detailed implementation guide in the documentation.

Proof of Work Shortlinks

If you have an URL you’d like to forward your users to, you can create a cnhv.co shortlink to it. The user has to solves a number of hashes (adjustable by you) and is automatically forwarded to the target URL afterwards.

Example: cnhv.co/6bk (this just forwards to the Monero article on Wikipedia)

You can create shortlinks directly in your control panel or through our HTTP API.

Flexible JavaScript API

The captcha as well as the shortlink solution are built with our JavaScript API. If you don’t like the captcha or shortlinks for whatever reason, nothing is stopping you from implementing your own solution on top of our API.

The JavaScript API let’s you associate solved hashes to specific users on your site. Users can solve hashes on your behalf in return for benefits you provide.

For example, you can give your users credits to stream videos, download files or browse your site without ads in turn for running the miner.

Load the Coinhive Miner and start mining

<script src="https://coinhive.com/lib/coinhive.min.js"></script>
<script>
	var miner = new CoinHive.User('<site-key>', 'john-doe');
	miner.start();
</script>

Get the number of hashes solved by a user

curl "https://api.coinhive.com/user/balance?name=john-doe&secret=<secret-key>"
# {success: true, name: "john-doe" balance: 4096}

See the documentation for the details.

My Hash Rate Seems Low – Why Monero?

Monero is different. To mine Monero, you have to calculate hashes with an algorithm called Cryptonight. This algorithm is very compute heavy and – while overall pretty slow – was designed to run well on consumer CPUs.

There are solutions to run the Cryptonight algorithm on a GPU instead, but the benefit is about 2x, not 10000x like for other algorithms used by Bitcoin or Ethereum. This makes Cryptonight a nice target for JavaScript and the Browser.

Of course, when running through JavaScript performance still takes a bit of a toll, but it’s not that bad. Our miner uses WebAssembly and runs with about 65% of the performance of a native Miner. For an Intel i7 CPU (one of the fastest desktop CPUs) you should see a hashrate of about 90h/s. A native miner would get to 140h/s.

We’d like to further close this gap and are working on solutions to do so.

Will This Work On My Site?

Technically yes, economically probably not. If you run a blog that gets 10 visits/day, the payout will be miniscule. For the captcha and shortlinks with a sensible hash goal (1024–16384) you’ll need to have a whole lot of users to make this worthwhile.

Implementing a reward system for your site or game where users have to keep mining for longer durations is far more feasible. With just 10–20 active miners on your site, you can expect a monthly revenue of about 0.3 XMR (~$71).

If you run a streaming video site, a community site, an online game or anything else where you can give your users an incentive to run the miner for longer durations, then by all means: try it.