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What if I told you... that you could run a website from behind Cloudflare and only have 385 daily requests miss their cache and go through to the origin service?
No biggy, unless... that was out of a total of more than 166M requests in the same period:
Yep, we just hit "five nines" of cache hit ratio on Pwned Passwords being 99.999%. Actually, it was 99.9998% but we're at the point now where that's just splitting hairs, let's talk about how we've managed to only have two requests in a million hit the origin, beginning with a bit of history:
Optimising Caching on Pwned Passwords (with Workers)- @troyhunt - https://t.co/KjBtCwmhmT pic.twitter.com/BSfJbWyxMy
— Cloudflare (@Cloudflare) August 9, 2018
Ah, memories 😊 Back then, Pwned Passwords was serving way fewer requests in a month than what we do in a day now and the cache hit ratio was somewhere around 92%. Put another way, instead of 2 in every million requests hitting the origin it was 85k. And we were happy with that! As the years progressed, the traffic grew and the caching model was optimised so our stats improved:
There it is - Pwned Passwords is now doing north of 2 *billion* requests a month, peaking at 91.59M in a day with a cache-hit ratio of 99.52%. All free, open source and out there for the community to do good with 😊 pic.twitter.com/DSJOjb2CxZ
— Troy Hunt (@troyhunt) May 24, 2022
And that's pretty much where we levelled out, at about the 99-and-a-bit percent mark. We were really happy with that as it was now only 5k requests per million hitting the origin. There was bound to be a number somewhere around that mark due to the transient nature of cache and eviction criteria inevitably meaning a Cloudflare edge node somewhere would need to reach back to the origin website and pull a new copy of the data. But what if Cloudflare never had to do that unless explicitly instructed to do so? I mean, what if it just stayed in their cache unless we actually changed the source file and told them to update their version? Welcome to Cloudflare Cache Reserve:
Ok, so I may have annotated the important bit but that's what it feels like - magic - because you just turn it on and... that's it. You still serve your content the same way, you still need the appropriate cache headers and you still have the same tiered caching as before, but now there's a "cache reserve" sitting between that and your origin. It's backed by R2 which is their persistent data store and you can keep your cached things there for as long as you want. However, per the earlier link, it's not free:
You pay based on how much you store for how long, how much you write and how much you read. Let's put that in real terms and just as a brief refresher (longer version here), remember that Pwned Passwords is essentially just 16^5 (just over 1 million) text files of about 30kb each for the SHA-1 hashes and a similar number for the NTLM ones (albeit slight smaller file sizes). Here are the Cache Reserve usage stats for the last 9 days:
We can now do some pretty simple maths with that and working on the assumption of 9 days, here's what we get:
2 bucks a day 😲 But this has taken nearly 16M requests off my origin service over this period of time so I haven't paid for the Azure Function execution (which is cheap) nor the egress bandwidth (which is not cheap). But why are there only 16M read operations over 9 days when earlier we saw 167M requests to the API in a single day? Because if you scroll back up to the "insert magic here" diagram, Cache Reserve is only a fallback position and most requests (i.e. 99.52% of them) are still served from the edge caches.
Note also that there are nearly 1M write operations and there are 2 reasons for this:
An untold number of businesses rely on Pwned Passwords as an integral part of their registration, login and password reset flows. Seriously, the number is "untold" because we have no idea who's actually using it, we just know the service got hit three and a quarter billion times in the last 30 days:
Giving consumers of the service confidence that not only is it highly resilient, but also massively fast is essential to adoption. In turn, more adoption helps drive better password practices, less account takeovers and more smiles all round 😊
As those remaining hash prefixes populate Cache Reserve, keep an eye on the "cf-cache-status" response header. If you ever see a value of "MISS" then congratulations, you're literally one in a million!
Full disclosure: Cloudflare provides services to HIBP for free and they helped in getting Cache Reserve up and running. However, they had no idea I was writing this blog post and reading it live in its entirety is the first anyone there has seen it. Surprise! 👋
I think I've pretty much captured it all in the title of this post but as of about a day ago, Pwned Passwords now has full parity between the SHA-1 hashes that have been there since day 1 and NTLM hashes. We always had both as a downloadable corpus but as of just over a year ago with the introduction of the FBI data feed, we stopped maintaining downloadable behemoths of data.
A little later, we added the downloader to make it easy to pull down the latest and greatest complete data set directly from the same API that so many of you have integrated into your own apps. But because we only had an API for SHA-1 hashes, the downloader couldn't grab the NTLM versions and increasingly, we had 2 corpuses well out of parity.
I don't know exactly why, but just over the last few weeks we've had a marked uptick in requests for an updated NTLM corpus. Obviously there's still a demand to run this against local Active Directory environments and clearly, the more up to date the hashes are the more effective they are at blocking the use of poor passwords.
So, Chief Pwned Passwords Wrangler Stefán Jökull Sigurðarson got to work and just went ahead and built it all for you. For free. In his spare time. As a community contribution. Seriously, have a look through the public GitHub repos and it's all his work ranging from the API to the Cloudflare Worker to the downloader so if you happen to come across him say, at NDC Oslo in a few months' time, show your appreciation and buy the guy a beer 🍺
Lastly, every time I look at how much this tool is being used, I'm a bit shocked at how big the numbers are getting:
That's well more than double the number of monthly requests from when I wrote the blog post about the FBI and NCA only just over a year ago, and I imagine that will only continue to increase, especially with today's announcement about NTLM hashes. Thank you to everyone that has taken this data and done great things with it, we're grateful that it's been put to good use and has undoubtedly helped an untold number of people to make better password choices 😊
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