Length Extension Attack Demonstration

Prefer to watch/listen than read? There’s a vloggy/video version of this post in which I explain all the key concepts and demonstrate an SHA-1 length extension attack against an imaginary site.

I understood the concept of a length traversal attack and when/how I needed to mitigate them for a long time before I truly understood why they worked. It took until work provided me an opportunity to play with one in practice (plus reading Ron Bowes’ excellent article on the subject) before I really grokked it.

Would you like to learn? I’ve put together a practical demo that you can try for yourself!

Screenshot of vulnerable site with legitimate "download" link hovered.
For the demonstration, I’ve built a skeletal stock photography site whose download links are protected by a hash of the link parameters, salted using a secret string stored securely on the server. Maybe they let authorised people hotlink the images or something.

You can check out the code and run it using the instructions in the repository if you’d like to play along.

Using hashes as message signatures

The site “Images R Us” will let you download images you’ve purchased, but not ones you haven’t. Links to the images are protected by a SHA-1 hash1, generated as follows:

Diagram showing SHA1 being fed an unknown secret key and the URL params "download=free" and outputting a hash as a "download key".
The nature of hashing algorithms like SHA-1 mean that even a small modification to the inputs, e.g. changing one character in the word “free”, results in a completely different output hash which can be detected as invalid.

When a “download” link is generated for a legitimate user, the algorithm produces a hash which is appended to the link. When the download link is clicked, the same process is followed and the calculated hash compared to the provided hash. If they differ, the input must have been tampered with and the request is rejected.

Without knowing the secret key – stored only on the server – it’s not possible for an attacker to generate a valid hash for URL parameters of the attacker’s choice. Or is it?

Changing download=free to download=valuable invalidates the hash, and the request is denied.

Actually, it is possible for an attacker to manipulate the parameters. To understand how, you must first understand a little about how SHA-1 and its siblings actually work:

SHA-1‘s inner workings

  1. The message to be hashed (SECRET_KEY + URL_PARAMS) is cut into blocks of a fixed size.2
  2. The final block is padded to bring it up to the full size.3
  3. A series of operations are applied to the first block: the inputs to those operations are (a) the contents of the block itself, including any padding, and (b) an initialisation vector defined by the algorithm.4
  4. The same series of operations are applied to each subsequent block, but the inputs are (a) the contents of the block itself, as before, and (b) the output of the previous block. Each block is hashed, and the hash forms part of the input for the next.
  5. The output of running the operations on the final block is the output of the algorithm, i.e. the hash.
Diagram showing message cut into blocks, the last block padded, and then each block being fed into a function along with the output of the function for the previous block. The first function, not having a previous block, receives the IV as its secondary input. The final function outputs the hash.
SHA-1 operates on a single block at a time, but the output of processing each block acts as part of the input of the one that comes after it. Like a daisy chain, but with cryptography.

In SHA-1, blocks are 512 bits long and the padding is a 1, followed by as many 0s as is necessary, leaving 64 bits at the end in which to specify how many bits of the block were actually data.

Padding the final block

Looking at the final block in a given message, it’s apparent that there are two pieces of data that could produce exactly the same output for a given function:

  1. The original data, (which gets padded by the algorithm to make it 64 bytes), and
  2. A modified version of the data, which has be modified by padding it in advance with the same bytes the algorithm would; this must then be followed by an additional block
Illustration showing two blocks: one short and padded, one pre-padded with the same characters, receiving the same IV and producing the same output.
A “short” block with automatically-added padding produces the same output as a full-size block which has been pre-populated with the same data as the padding would add.5
In the case where we insert our own “fake” padding data, we can provide more message data after the padding and predict the overall hash. We can do this because we the output of the first block will be the same as the final, valid hash we already saw. That known value becomes one of the two inputs into the function for the block that follows it (the contents of that block will be the other input). Without knowing exactly what’s contained in the message – we don’t know the “secret key” used to salt it – we’re still able to add some padding to the end of the message, followed by any data we like, and generate a valid hash.

Therefore, if we can manipulate the input of the message, and we know the length of the message, we can append to it. Bear that in mind as we move on to the other half of what makes this attack possible.

Parameter overrides

“Images R Us” is implemented in PHP. In common with most server-side scripting languages, when PHP sees a HTTP query string full of key/value pairs, if a key is repeated then it overrides any earlier iterations of the same key.

Illustration showing variables in a query string: "?one=foo&two=bar&one=baz". When parsed by PHP, the second value of "one" ("baz") only is retained.
Many online sources say that this “last variable matters” behaviour is a fundamental part of HTTP, but it’s not: you can disprove is by examining $_SERVER['QUERY_STRING'] in PHP, where you’ll find the entire query string. You could even implement your own query string handler that instead makes the first instance of each key the canonical one, if you really wanted.6
It’d be tempting to simply override the download=free parameter in the query string at “Images R Us”, e.g. making it download=free&download=valuable! But we can’t: not without breaking the hash, which is calculated based on the entire query string (minus the &key=... bit).

But with our new knowledge about appending to the input for SHA-1 first a padding string, then an extra block containing our payload (the variable we want to override and its new value), and then calculating a hash for this new block using the known output of the old final block as the IV… we’ve got everything we need to put the attack together.

Putting it all together

We have a legitimate link with the query string download=free&key=ee1cce71179386ecd1f3784144c55bc5d763afcc. This tells us that somewhere on the server, this is what’s happening:

Generation of the legitimate hash for the (unknown) secret key a string download=free, with algorithmic padding shown.
I’ve drawn the secret key actual-size (and reflected this in the length at the bottom). In reality, you might not know this, and some trial-and-error might be necessary.7
If we pre-pad the string download=free with some special characters to replicate the padding that would otherwise be added to this final8 block, we can add a second block containing an overriding value of download, specifically &download=valuable. The first value of download=, which will be the word free followed by a stack of garbage padding characters, will be discarded.

And we can calculate the hash for this new block, and therefore the entire string, by using the known output from the previous block, like this:

The previous diagram, but with the padding character manually-added and a second block containing "&download=valuable". The hash is calculated using the known output from the first block as the IV to the function run over the new block, producing a new hash value.
The URL will, of course, be pretty hideous with all of those special characters – which will require percent-encoding – on the end of the word ‘free’.

Doing it for real

Of course, you’re not going to want to do all this by hand! But an understanding of why it works is important to being able to execute it properly. In the wild, exploitable implementations are rarely as tidy as this, and a solid comprehension of exactly what’s happening behind the scenes is far more-valuable than simply knowing which tool to run and what options to pass.

That said: you’ll want to find a tool you can run and know what options to pass to it! There are plenty of choices, but I’ve bundled one called hash_extender into my example, which will do the job pretty nicely:

$ docker exec hash_extender hash_extender \
    --format=sha1 \
    --data="download=free" \
    --secret=16 \
    --signature=ee1cce71179386ecd1f3784144c55bc5d763afcc \
    --append="&download=valuable" \
    --out-data-format=html
Type: sha1
Secret length: 16
New signature: 7b315dfdbebc98ebe696a5f62430070a1651631b
New string: download%3dfree%80%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%e8%26download%3dvaluable

I’m telling hash_extender:

  1. which algorithm to use (sha1), which can usually be derived from the hash length,
  2. the existing data (download=free), so it can determine the length,
  3. the length of the secret (16 bytes), which I’ve guessed but could brute-force,
  4. the existing, valid signature (ee1cce71179386ecd1f3784144c55bc5d763afcc),
  5. the data I’d like to append to the string (&download=valuable), and
  6. the format I’d like the output in: I find html the most-useful generally, but it’s got some encoding quirks that you need to be aware of!

hash_extender outputs the new signature, which we can put into the key=... parameter, and the new string that replaces download=free, including the necessary padding to push into the next block and your new payload that follows.

Unfortunately it does over-encode a little: it’s encoded all the& and = (as %26 and %3d respectively), which isn’t what we wanted, so you need to convert them back. But eventually you end up with the URL: http://localhost:8818/?download=free%80%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%e8&download=valuable&key=7b315dfdbebc98ebe696a5f62430070a1651631b.

Browser at the resulting URL, showing the "valuable" image (a pile of money).
Disclaimer: the image you get when you successfully exploit the test site might not actually be valuable.

And that’s how you can manipulate a hash-protected string without access to its salt (in some circumstances).

Mitigating the attack

The correct way to fix the problem is by using a HMAC in place of a simple hash signature. Instead of calling sha1( SECRET_KEY . urldecode( $params ) ), the code should call hash_hmac( 'sha1', urldecode( $params ), SECRET_KEY ). HMACs are theoretically-immune to length extension attacks, so long as the output of the hash function used is functionally-random9.

Ideally, it should also use hash_equals( $validDownloadKey, $_GET['key'] ) rather than ===, to mitigate the possibility of a timing attack. But that’s another story.

Footnotes

1 This attack isn’t SHA1-specific: it works just as well on many other popular hashing algorithms too.

2 SHA-1‘s blocks are 64 bytes long; other algorithms vary.

3 For SHA-1, the padding bits consist of a 1 followed by 0s, except the final 8-bytes are a big-endian number representing the length of the message.

4 SHA-1‘s IV is 67452301 EFCDAB89 98BADCFE 10325476 C3D2E1F0, which you’ll observe is little-endian counting from 0 to F, then back from F to 0, then alternating between counting from 3 to 0 and C to F. It’s considered good practice when developing a new cryptographic system to ensure that the hard-coded cryptographic primitives are simple, logical, independently-discoverable numbers like simple sequences and well-known mathematical constants. This helps to prove that the inventor isn’t “hiding” something in there, e.g. a mathematical weakness that depends on a specific primitive for which they alone (they hope!) have pre-calculated an exploit. If that sounds paranoid, it’s worth knowing that there’s plenty of evidence that various spy agencies have deliberately done this, at various points: consider the widespread exposure of the BULLRUN programme and its likely influence on Dual EC DRBG.

5 The padding characters I’ve used aren’t accurate, just representative. But there’s the right number of them!

6 You shouldn’t do this: you’ll cause yourself many headaches in the long run. But you could.

7 It’s also not always obvious which inputs are included in hash generation and how they’re manipulated: if you’re actually using this technique adversarily, be prepared to do a little experimentation.

8 In this example, the hash operates over a single block, but the exact same principle applies regardless of the number of blocks.

9 Imagining the implementation of a nontrivial hashing algorithm, the predictability of whose output makes their HMAC vulnerable to a length extension attack, is left as an exercise for the reader.

Screenshot of vulnerable site with legitimate "download" link hovered.× Browser at the resulting URL, showing the "valuable" image (a pile of money).×

Emoji Reactions

I added a stupid feature to my blog.

On some posts, including this one, you can now send an “emoji reaction”. Y’know, for if you’re too lazy to write a comment.

The available reactions vary by post.

That is all.

The Frosted Pane

Pagan Wanderer Lu‘s new album Planets In The Wires dropped today, and I just cried my eyes out at track 5 (The Frosted Pane).

It opens almost apologetically, like an explanation for the gap in new releases for most of the twenty-teens. But it quickly becomes a poetic exploration of a detached depression of a man trapped under the weight of the world. It’s sad, and beautiful, and relatable.

It Takes Two

Lately, Ruth and I have been learning to dance Argentine Tango.

In a church hall, its walls decorated with colourful cloths, Dan and Ruth stand in a large circle of people, watching a man and a woman preparing to demonstrate some tango steps.
Stand with both feet together on the floor? Sure, I can do that one.

Let me tell you everything I know about tango1:

  1. It takes two to tango.
  2. I am not very good at tango.
Dan, wearing a black t-shirt and holding a glass of wine, looks sceptically at the camera as he stands in front of a television screen showing a couple dancing, with the title frame "La Caminata: Introduction to Walking in Tango (Core Steps)".
Our lessons started online, in our own living room, with videos from Tango Stream‘s “Tango Basics” series. It was a really good introduction and I’d recommend it, but it’s no substitute for practice!

This adventure began, in theory at least, on my birthday in January. I’ve long expressed an interest in taking a dance class together, and so when Ruth pitched me a few options for a birthday gift, I jumped on the opportunity to learn tango. My knowledge of the dance was basically limited to what I’d seen in films and television, but it had always looked like such an amazing dance: careful, controlled… synchronised, sexy.

After shopping around for a bit, Ruth decided that the best approach was for us to do a “beginners” video course in the comfort of our living room, and then take a weekend getaway to do an “improvers” class.

After all, we’d definitely have time to complete the beginners’ course and get a lot of practice in before we had to take to the dance floor with a group of other “improvers”, right?2

Dan and Ruth sat on opposite sides of a table on a train, with darkness outside the window behind, raising tumbler glasses full of prosecco and smiling.
By the time we were riding the train up to Edinburgh, we’d watched all the videos in our beginners’ course, and tried all of the steps in isolation… but we’d had barely any opportunity to combine them into an actual dance.

Okay, let me try again to enumerate you everything I actually know about tango3:

  1. Essentials. A leader and follower4 hold one another’s upper torso closely enough that, with practice, each can intuit from body position where the other’s feet are without looking. While learning, you will not manage to do this, and you will tread on one another’s toes.
  2. The embrace. In the embrace, one side – usually the leader’s left – is “open”, with the dancers’ hands held; the other side is “closed”, with the dancers holding one another’s bodies. Generally, you should be looking at one another or towards the open side. But stop looking at your feet: you should know where your own feet are by proprioception, and you know where your partners’ feet are by guesswork and prayer.
  3. The walk. You walk together, (usually) with opposite feet moving in-sync so that you can be close and not tread on one another’s toes, typically forward (from the leader’s perspective) but sometimes sideways or even backwards (though not usually for long, because it increases the already-inevitable chance that you’ll collide embarrassingly with other couples).
  4. Movement. Through magic and telepathy a good connection with one another, the pair will, under the leader’s direction, open opportunities to perform more advanced (but still apparently beginner-level) steps and therefore entirely new ways to mess things up. These steps include:
    • Forward ochos. The follower stepping through a figure-eight (ocho) on the closed side, or possibly the open side, but they probably forget which way they were supposed to turn when they get there, come out on the wrong foot, and treat on the leader’s toes.
    • Backwards ochos. The follower moves from side to side or in reverse through a series of ochos, until the leader gets confused which way they’re supposed to pivot to end the maneuver and both people become completely confused and unstuck.
    • The cross. The leader walks alongside the follower, and when the leader steps back the follower chooses to assume that the leader intended for them to cross their legs, which opens the gateway to many other steps. If the follower guesses incorrectly, they probably fall over during that step. If the follower guesses correctly but forgets which way around their feet ought to be, they probably fall over on the very next step. Either way, the leader gets confused and does the wrong thing next.
    • Giros. One or both partners perform a forwards step, then a sideways step, then a backwards step, then another sideways step, starting on the inside leg and pivoting up to 270° with each step such that the entire move rotates them some portion of a complete circle. In-sync with one another, of course.
    • Sacadas. Because none of the above are hard enough to get right together, you should start putting your leg out between your partner’s leg and try and trip them up as they go. They ought to know you’re going to do this, because they’ve got perfect predictive capabilities about where your feet are going to end, remember? Also remember to use the correct leg, which might not be the one you expect, or you’ll make a mess of the step you’ll be doing in three beats’ time. Good luck!
    • Barridas and mordidas. What, you finished the beginners’ course? Too smart to get tripped up by your partner’s sacada any more? Well now it’s time to start kicking your partner’s feet out from directly underneath them. That’ll show ’em.
  5. Style. All of the above should be done gracefully, elegantly, with perfect synchronicity and in time with the music… oh, and did I mention you should be able to improve the whole thing on the fly, without pre-communication with your partner. 😅
Photograph of a small laminated instruction sheet on a golden tablecloth. Titled "Norteña Tango", it reads: Let's make this an amazing weekend. We are all here to dance, so let's look around us and try to make sure that everyone is dancing. We'd love it if you would follow the lines of dance by moving around the floor steadily, try using the cabeceo, leave space between you and the couple in front, make use of the corners of the dance floor, stay in the same lane where possible, take care when entering the dance floor, clear the floor and change partners during the cortinas. It would be great if you could avoid overtaking other couples on the floor, walking (other than when dancing) on the floor.
Just when you think you’ve worked out the basic rules of tango, you find a leaflet on your table with some rules of the dancefloor to learn, too!

Ultimately, it was entirely our own fault we felt out-of-our-depth up in Edinburgh at the weekend. We tried to run before we could walk, or – to put it another way – to milonga before we could caminar.

A somewhat-rushed video course and a little practice on carpet in your living room is not a substitute for a more-thorough práctica on a proper-sized dance floor, no matter how often you and your partner use any excuse of coming together (in the kitchen, in an elevator, etc.) to embrace and walk a couple of steps! Getting a hang of the fluid connections and movement of tango requires time, and practice, and discipline.

Photograph of paving slabs: a glyph of a walking person, signifying "walk here", has been painted onto the flagstones, but the stones have since been lifted and replaced in slightly different locations, making the person appear "scrambled".
Got the feeling that your body and your feet aren’t moving in the same direction? That’s tango!

But, not least because of our inexperience, we did learn a lot during our weekend’s deep-dive. We got to watch (and, briefly, partner with) some much better dancers and learned some advanced lessons that we’ll doubtless reflect back upon when we’re at the point of being ready for them. Because yes: we are continuing! Our next step is a Zoom-based lesson, and then we’re going to try to find a more-local group.

Also, we enjoyed the benefits of some one-on-one time with Jenny and Ricardo, the amazingly friendly and supportive teachers whose video course got us started and whose in-person event made us feel out of our depth (again: entirely our own fault).

If you’ve any interest whatsoever in learning to dance tango, I can wholeheartedly recommend Ricardo and Jenny Oria as teachers. They run courses in Edinburgh and occasionally elsewhere in the UK as well as providing online resources, and they’re the most amazingly supportive, friendly, and approachable pair imaginable!

Just… learn from my mistake and start with a beginner course if you’re a beginner, okay? 😬

Footnotes

1 I’m exaggerating how little I know for effect. But it might not be as much of an exaggeration as you’d hope.

2 We did not.

3 Still with a hint of sarcasm, though.

4 Tango’s progressive enough that it’s come to reject describing the roles in binary gendered terms, using “leader” and “follower” in place of what was once described as “man” and “woman”, respectively. This is great for improving access to pairs of dancers who don’t consist of a man and a woman, as well as those who simply don’t want to take dance roles imposed by their gender.

In a church hall, its walls decorated with colourful cloths, Dan and Ruth stand in a large circle of people, watching a man and a woman preparing to demonstrate some tango steps.× Dan, wearing a black t-shirt and holding a glass of wine, looks sceptically at the camera as he stands in front of a television screen showing a couple dancing, with the title frame "La Caminata: Introduction to Walking in Tango (Core Steps)".× Dan and Ruth sat on opposite sides of a table on a train, with darkness outside the window behind, raising tumbler glasses full of prosecco and smiling.× Photograph of a small laminated instruction sheet on a golden tablecloth. Titled "Norteña Tango", it reads: Let's make this an amazing weekend. We are all here to dance, so let's look around us and try to make sure that everyone is dancing. We'd love it if you would follow the lines of dance by moving around the floor steadily, try using the cabeceo, leave space between you and the couple in front, make use of the corners of the dance floor, stay in the same lane where possible, take care when entering the dance floor, clear the floor and change partners during the cortinas. It would be great if you could avoid overtaking other couples on the floor, walking (other than when dancing) on the floor.× Photograph of paving slabs: a glyph of a walking person, signifying "walk here", has been painted onto the flagstones, but the stones have since been lifted and replaced in slightly different locations, making the person appear "scrambled".×

Household Finances Revisited

Almost a decade ago I shared a process that my domestic polyfamily and I had been using (by then, for around four years) to manage our household finances. That post isn’t really accurate any more, so it’s time for an update (there’s a link if you just want the updated spreadsheet):

Dan, wearing a WordPress Pride "rainbow flag on black" t-shirt, sits on a park bench alongside a French Bulldog (with her tongue sticking out) and a young boy (throwing a peace sign, wearing a pink cycle helmet and a blue school uniform).
Our household costs have increased considerably over the last decade, not least because children and pets are expensive (who knew?).

Sample data

For my examples below, assume a three-person family. I’m using unrealistic numbers for easy arithmetic.

  • Alice earns £2,000, Bob earns £1,000, and Chris earns £500, for a total household income of £3,500.
  • Alice spends £1,450, Bob £800, and Chris £250, for a total household expenditure of £2,500.

Model #1: Straight Split

We’ve never done things this way, but for completeness sake I’ll mention it: the simplest way that households can split their costs is by dividing them between the participants equally: if the family make a £60 shopping trip, £20 should be paid by each of Alice, Bob, and Chris.

My example above shows exactly why this might not be a smart choice: this model would have each participant contribute £833.33 over the course of the month, which is more than Chris earned. If this month is representative, then Chris will gradually burn through their savings and go broke, while Alice will put over a grand into her savings account every month!

Photograph of the Statue of Lenin in Independence Square, Minsk: Government House #1 stands behind a large metal statue of Vladimir Lenin, looking to his right.
“Land, Bread, Peace… and Spreadsheets!”

Model #2: Income-Assessed

We’re a bunch of leftie socialist types, and wanted to reflect our political outlook in our household finances, too. So rather than just splitting our costs equally between us, we initially implemented a means-assessment system based on the relative differences between our incomes. The thinking was that somebody that earns twice as much should contribute twice as much towards the costs of running the household.

Using our example family above, here’s how that might look:

  • Alice earned 57% of the household income, so she should have contributed 57% of the household costs: £1,425. She overpaid by £25.
  • Bob earned 29% of the household income, so he should have contributed 29% of the household costs: £725. He overpaid by £75.
  • Chris earned 14% of the household income, so they should have contributed 14% of the household costs: £350. They underpaid by £100.
  • Therefore, at the end of the month Chris should settle up by giving £25 to Alice and £75 to Bob.

By analogy: The “Income-Assessed” model is functionally equivalent to splitting each and every expense according to the participants income – e.g. if a £100 bill landed on their doormat, Alice would pay £57, Bob £29, and Chris £14 of it – but has the convenience that everybody just pays for things “as they go along” and then square everything up when their paycheques come in.

Photograph showing a detached white house clad in scaffolding, under a clear blue sky.
You know what else is surprisingly expensive? Having the roof of your house taken off.

Over time, our expenditures grew and changed and our incomes grew, but they didn’t do so in an entirely simple fashion, and we needed to make some tweaks to our income-assessed model of household finance contributions. For example:

  • Gross vs Net Income: For a while, some of our incomes were split into a mixture of employed income (on which income tax was paid as-we-earned) and self-employed income (for which income tax would be calculated later), making things challenging. We agreed that net income (i.e. take-home pay) was the correct measure for us to use for the income-based part of the calculation, which also helped keep things fair as some of us began to cross into and out of the higher earner tax bracket.
  • Personal Threshold: At times, a subset of us earned a disproportionate portion of the household income (there were short periods where one of us earned over 50% of the household income; at several other times two family members each earned thrice that of the third). Our costs increased too, but this imposed an regressive burden on the lower-earner(s), for whom those costs represented a greater proportion of their total income. To attempt to mitigate this, we introduced a personal threshold somewhat analogous to the income tax “personal allowance” (the policy that means that you don’t pay tax on your first £12,570 of income).

Eventually, we came to see that what we were doing was trying to patch a partially-broken system, and tried something new!

Model #3: Same-Residual

In 2022, we transitioned to a same-residual system that attempts to share out out money in an even-more egalitarian way. Instead of each person contributing in accordance with their income, the model attempts to leave each person with the same average amount of disposable personal income at the end. The difference is most-profound where the relative incomes are most-diverse.

With the example family above, that would mean:

  • The household earned £3,500 and spent £2,500, leaving £1,000. Dividing by 3 tells us that each person should have £333.33 after settling up.
  • Alice earned earned £2,000 and spent £1,450, so she has £550 left. That’s £216.67 too much.
  • Bob earned earned £1,000 and spent £800, so she has £200 left. That’s £133.33 too little.
  • Chris earned earned £500 and spent £250, so she has £250 left. That’s £83.33 too little.
  • Therefore, at the end of the month Alice should settle up by giving £133.33 to Bob and £83.33 to Chris (note there’s a 1p rounding error).

That’s a very different result than the Income-Assessed calculation came up with for the same family! Instead of Chris giving money to Alice and Bob, because those two contributed to household costs disproportionately highly for their relative incomes, Alice gives money to Bob and Chris, because their incomes (and expenditures) were much lower. Ignoring any non-household costs, all three would expect to have the same bank balance at the start of the month as at the end, after settlement.

By analogy: The “Same-Residual” model is functionally equivalent to having everybody’s salary paid into a shared bank account, out of which all household expenditures are paid, and at the end of the month everything that’s left in the bank account gets split equally between the participants.

Screenshot showing a sample filled verison of the spreadsheet.
Our version of the spreadsheet has inherited a lot of hacky edges, many for now-unused functionality.

We’ve made tweaks to this model, too, of course. For example: we’ve set a “target” residual and, where we spend little enough in a month that we would each be eligible for more than that, we instead sweep the excess into our family savings account. It’s a nice approach to help build up a savings reserve without feeling a pinch.

I’m sure our model will continue to evolve, as it has for the last decade and a half, but for now it seems stable, fair, and reasonable. Maybe it’ll work for your household too (whether or not you’re also a polyamorous family!): take a look at the spreadsheet in Google Drive and give it a go.

Dan, wearing a WordPress Pride "rainbow flag on black" t-shirt, sits on a park bench alongside a French Bulldog (with her tongue sticking out) and a young boy (throwing a peace sign, wearing a pink cycle helmet and a blue school uniform).× Photograph of the Statue of Lenin in Independence Square, Minsk: Government House #1 stands behind a large metal statue of Vladimir Lenin, looking to his right.× Photograph showing a detached white house clad in scaffolding, under a clear blue sky.× Screenshot showing a sample filled verison of the spreadsheet.×

Pen Pals Wanted

Semi-inspired by a similar project by Kev Quirk, I’ve got a project I want to run on my blog in 2024.

I want you to be my pen pal for a month. Get in touch by emailing penpals@danq.me or any other way you like and let’s do this!

Traditional inkwell and pen, the latter held in an inkstained finger grip, being used to write a letter on unbleached paper atop a wooden desk.
We’ll use email, though, not paper.

I don’t know much about the people who read my blog, whether they’re ad-hoc visitors or regular followers1.

Dan, wearing a black t-shirt and jeans, sits hunched over a keyboard with Pride-coloured keys, looking thoughtfully at a widescreen monitor. On the monitor is a mocked-up screenshot showing site analytics for DanQ.me, but with question marks for every datapoint.
I’m not interested in collecting statistics about people reading this post. I’m interested in meeting them.

So here’s the plan: I’m looking to do is to fill a “dance card” of interesting people each of with whom I’ll “pen pal” for a month.

The following month, I’ll blog about the experience: who I met, what I learned about them, what I learned about myself. Have a look below and see if there’s a slot for you: I’d love to chat to you about, well – anything!

My goals:

    • Get inspired to blog about new/different things (and hopefully help inspire others to do the same).
    • Connect with a dozen folks on a more-interpersonal level than I normally do via my blog.
  • Maybe even make, or deepen, some friendships!

The “rules”:

  • Aiming for at least 3 email exchanges over a month. Maybe more.2
  • Email is the medium.3
  • There’s no specific agenda: I promise to bring what I’ve been thinking about and working on, and possibly a spicy conversation-starter from LetsLifeChat.com. You bring whatever you like. No topic is explicitly off the table unless somebody says it is (which anybody can do at any time, for any or no reason).
  • I’ll blog a summary of my experience the month afterwards, but I won’t share anything without permission. I’ll happily share an unpublished draft with each penpal first so they can veto any bits they don’t like. I’ll refer to you by whatever name, link etc. suits you best.
  • If you have a blog/digital garden/social presence of any kind, you’re welcome to blog about it too. Or not: entirely up to you!

Who’s in so far?

Want in? Leave a comment, at-me on the Fediverse @dan@danq.me, fill my contact form, or just email penpals@danq.me. Okay; looks like I’ve got a full year of people to meet! Awesome!

Penpal with… …during… …and blog in: Notes:
Colin Walker December 2023 January 2024 Colin’s announcement
Thom Denholm January 2024 February 2024
Ru February 2024 March 2024
Dr. Alex Bowyer March 2024 April 2024 Agreement via LinkedIn
Roslyn Cook April 2024 May 2024
Garrett Coakley May 2024 June 2024
Derek Kedziora June 2024 July 2024
Aarón Fas July 2024 August 2024
Cal Desmond-Pearson August 2024 September 2024
Tyoma September 2024 October 2024
Farai October 2024 November 2024
Katie November 2024 December 2024 Katie’s comment

I’ll update this table as people get in touch.

Who do I want to meet?

You! If you’re reading this, you’re probably somebody I want to meet! But I’d be especially interested in penpalling with people who tick one or more of the following boxes:

  • Personal bloggers at the edges of or just outside my usual social circles. Maybe you’re an IndieWebRSS Club, or Geminispace explorer?
  • Regular readers, whether you just skim the post titles and dive in once in a blue moon or read every post and comment on the things you care about.
  • Automatticians from parts of the company I don’t get to interact with. Let’s build some bridges!
  • People whose interests overlap with mine in any way, large or small. That overlap might be technology (web standards, accessibility, security, blogging, open source…), hobbies (GPS sports, board games, magic, murder mysteries, science fiction, getting lost on Wikipedia…), volunteering (third sector support, tech for good, diversity in tech…), social (queer issues, polyamory, socialism…), or something else entirely.
  • Missed connections. Did we meet briefly or in-passing (conferences, meetups, friends-of-friends, overlapping volunteering circles) but not develop anything further? I’d love to pick up where we left off!
  • Distant- and nearly-friends. Did we drift apart long ago, or never quite move into one another’s orbit in the first place? This could be your excuse to touch bases!

If you read this far and didn’t email penpals@danq.me yet, go do that. I’m looking forward to hearing from you!

Footnotes

1 Not-knowing who reads my blog might come at least in part from the fact that I actively sabotage any plugin that might give me any analytics! One might say I’ve shot myself in the foot, there.

2 If we stay in touch afterwards that’s fine too, but it’s not essential.

3 I’m looking for longer-form, but slower, communication than you get via e.g. instant messengers and whatnot: a more “penpal” experience.

Traditional inkwell and pen, the latter held in an inkstained finger grip, being used to write a letter on unbleached paper atop a wooden desk.× Dan, wearing a black t-shirt and jeans, sits hunched over a keyboard with Pride-coloured keys, looking thoughtfully at a widescreen monitor. On the monitor is a mocked-up screenshot showing site analytics for DanQ.me, but with question marks for every datapoint.×

My Default Apps at the End of 2023

Kev Quirk, Colin Walker, and other cool kids I follow online made it sound fun to share your “lifestack” as we approach the end of 2023.

So here’s mine: my digital “everyday carry” list of the tools and services I routinely use:

  • 📨 Mail Service: Proton Mail
  • 📮 Mail Client: Thunderbird (Desktop), Proton Mail App (Android), Proton Mail webmail (anywhere else)
  • 📝 Notes: Obsidian, Syncthing (for cross-device sync)
  • To-Do: Obsidian, physical notepad [not happy with this; want something more productive]
  • 📆 Calendar: Google Calendar (via Thunderbird on Desktop) [not happy with this; want something not-Google – still waiting on Proton Calendar getting good!]
  • 🙍🏻‍♂️ Contacts: Proton Mail
  • 📖 RSS Service: FreshRSS, selfhosted
  • 🗞️ RSS Client: FreshRSS (Desktop), FeedMe (Android)
  • ⌨️ Launcher: RayCast (MacOS), PowerToys Run (Windows)
  • ☁️ Cloud storage: ownCloud (selfhosted)
  • 🌅 Photo library: plain old directories! [would like: something selfhosted, mostly filesystem-driven, with Web interface]
  • 🌐 Web Browser: Firefox (everywhere)
  • 💬 Chat: Slack, WhatsApp, Signal, Telegram
  • 🔖 Bookmarks: Firefox (easy access), Wallabag (selfhosted, for long-term archiving)
  • 📚 Reading: dead tree format [my Kindle v2 died and I’m seeking a non-Amazon replacement; suggestions welcome], Calibre
  • 📜 Word Processing: Microsoft Word, Google Docs
  • 📈 Spreadsheets: Microsoft Excel, Google Sheets
  • 📊 Presentations: reveal.js
  • 🛒 Shopping Lists: pen and paper
  • 💰 Personal Finance: Google Sheets
  • 🎵 Music: YouTube Music [not entirely happy with it; considering replacement]
  • 🎤 Podcasts: FreshRSS; experimenting with Pocket Casts
  • 🔐 Password Management: KeePassXC, Syncthing (for cross-device sync)
  • 🤦‍♂️ Social Media: Mastodon, selfhosted
  • 🔎 Search: DuckDuckGo
  • 🧮 Code Editor: Sublime Text
  • ⌨️ KVM: Barrier
  • 🗺️ Navigation: OpenStreetMap, Google Maps, Talkietoaster (Garmin Montana)
  • 📍 Location Tracking: uLogger
  • 🔗 Blog: WordPress, selfhosted

ET App

Travelling around Edinburgh by tram this weekend, I kept being advertised the “ET app”.

Print advertisement for the "ET App", stating: Download the et app to purchase your mobile tickets including bundle deals.

I didn’t install the app, in case it was bundled with spyware.

After all, everybody my age knows: ET phones home.

Print advertisement for the "ET App", stating: Download the et app to purchase your mobile tickets including bundle deals.×

Bramble

Fresh D&D campaign with some Abnib folks! I’m playing a Harengon Barbarian.

I’m a fierce bunny rabbit!

Composite photo showing on the left a render of large anthropomorphic rabbit with chestnut-coloured fur, brandishing a shield and a warhammer; on the right Dan, wearing a rabbit ear headband and with a nose and whiskers painted on his face, looking threatening (insofar as it's possible to do so while looking like a bunny).

Composite photo showing on the left a render of large anthropomorphic rabbit with chestnut-coloured fur, brandishing a shield and a warhammer; on the right Dan, wearing a rabbit ear headband and with a nose and whiskers painted on his face, looking threatening (insofar as it's possible to do so while looking like a bunny).×

Gemini Squared

How did I never think of accessing Gemini (the protocol) on my Gemini (portable computer) before today?

Of course, I recently rehomed my Gemini so instead I had to access Gemini on my Cosmo (Gemini’s successor), which isn’t nearly as cool.1

Dan's recent article, "Gemini and Spartan without a browser", displayed over Gemini on the screen of a Planet Computers Cosmo palmtop.

Footnotes

1 Still pretty cool though. Reminds me of using Lynx on my Psion 5mx last millenium…

Dan's recent article, "Gemini and Spartan without a browser", displayed over Gemini on the screen of a Planet Computers Cosmo palmtop.×

Gemini and Spartan without a browser

A particular joy of the Gemini and Spartan protocols – and the Markdown-like syntax of Gemtext – is their simplicity.

Screenshot showing this blog post as viewed over the Gemini protocol in the Lagrange browser
The best way to explore Geminispace is with a browser like Lagrange browser, of course.

Even without a browser, you can usually use everyday command-line tools that you might have installed already to access relatively human-readable content.

Here are a few different command-line options that should show you a copy of this blog post (made available via CapsulePress, of course):

Gemini

Gemini communicates over a TLS-encrypted channel (like HTTPS), so we need a to use a tool that speaks the language. Luckily: unless you’re on Windows you’ve probably got one installed already1.

Using OpenSSL

This command takes the full gemini:// URL you’re looking for and the domain name it’s at. 1965 refers to the port number on which Gemini typically runs –

printf "gemini://danq.me/posts/gemini-without-a-browser\r\n" | \
  openssl s_client -ign_eof -connect danq.me:1965

Using GnuTLS

GnuTLS closes the connection when STDIN closes, so we use cat to keep it open. Note inclusion of --no-ca-verification to allow self-signed certificates (optionally add --tofu for trust-on-first-use support, per the spec).

{ printf "gemini://danq.me/posts/gemini-without-a-browser\r\n"; cat -; } | \
  gnutls-cli --no-ca-verification danq.me:1965

Using Ncat

Netcat reimplementation Ncat makes Gemini requests easy:

printf "gemini://danq.me/posts/gemini-without-a-browser\r\n" | \
  ncat --ssl danq.me 1965

Spartan

Spartan is a little like “Gemini without TLS“, but it sports an even-more-lightweight request format which makes it especially easy to fudge requests2.

Using Telnet

Note the use of cat to keep the connection open long enough to get a response, as we did for Gemini over GnuTLS.

{ printf "danq.me /posts/gemini-without-a-browser 0\r\n"; cat -; } | \
  telnet danq.me 300

Using cURL

cURL supports the telnet protocol too, which means that it can be easily coerced into talking Spartan:

printf "danq.me /posts/gemini-without-a-browser 0\r\n" | \
  curl telnet://danq.me:300

Using Ncat/Netcat

Because TLS support isn’t needed, this also works perfectly well with Netcat – just substitute nc/netcat or whatever your platform calls it in place of ncat:

printf "danq.me /posts/gemini-without-a-browser 0\r\n" | \
  ncat danq.me 300

I hope these examples are useful to somebody debugging their capsule, someday.

Footnotes

1 You can still install one on Windows, of course, it’s just less-likely that your operating system came with such a command-line tool built-in

2 Note that the domain and path are separated in a Spartan request and followed by the size of the request payload body: zero in all of my examples

Screenshot showing this blog post as viewed over the Gemini protocol in the Lagrange browser×

Making WordPress Fast (The Hard Way)

This isn’t the guide for you

The Internet is full of guides on easily making your WordPress installation run fast. If you’re looking to speed up your WordPress site, you should go read those, not this.

Those guides often boil down to the same old tips:

  1. uninstall unnecessary plugins,
  2. optimise caching (both on the server and, via your headers, on clients/proxies),
  3. resize your images properly and/or ensure WordPress is doing this for you,
  4. use a CDN (and use DNS prefetch hints)1,
  5. tune your PHP installation so it’s got enough memory, keeps a process alive, etc.,
  6. ensure your server is minifying2 and compressing files, and
  7. run it on a faster server/behind a faster connection3
You’ve heard those tips before, right? Today, let’s try something different.

The hard way

This article is for people who aren’t afraid to go tinkering in their WordPress codebase to squeeze a little extra (real world!) performance.

It’s for people whose neverending quest for perfection is already well beyond the point of diminishing returns.

But mostly, it’s for people who want to gawp at me, the freak who actually did this stuff just to make his personal blog a tiny bit nippier without spending an extra penny on hosting.

You shouldn’t use Lighthouse as your only measure of your site’s performance. But it’s still reassuring when you get to see those fireworks!

Don’t start with the hard way. Exhaust all the easy solutions – or at least, make a conscious effort which easy solutions to enact or reject – first. Only if you really want to get into the weeds should you actually try doing the things I propose here. They’re not for most sites, and they’re not the for faint of heart.

Performance is a tradeoff. Every performance improvement costs you something else: time, money, DX, UX, etc. What you choose to trade for performance gains depends on your priority of constituencies, which may differ from mine.4

This is not a recipe book. This won’t tell you what code to change or what commands to run. The right answers for your content will be different than the right answers for mine. Also: you shouldn’t change what you don’t understand! But I hope these tips will help you think about what questions you need to ask to make your site blazing fast.

Okay, let’s get started…

1. Backstab the plugins you can’t live without

If there are plugins you can’t remove because you depend upon their functionality, and those plugins inject content (especially JavaScript) on the front-end… backstab them to undermine that functionality.

For example, if you want Jetpack‘s backup and downtime monitoring features, but you don’t want it injecting random <link rel='stylesheet' id='...-jetpack-css' href='...' media='all' />‘s (an extra stylesheet to download and parse) into your pages: find the add_filter hook it uses and remove_filter it in your theme5.

Screenshot of a code editor showing a typical WordPress theme's header.php, but with the wp_head() line commented out.
Alternatively, entirely remove the wp_head() and manually reimplement the functionality you actually need. Insert your own joke about “Headless WordPress” here.

Better yet, remove wp_head() from your theme entirely6. Now, instead of blocking the hooks you don’t want polluting your <head>, you’re specifically allowing only those you want. You’ll want to take care to get some semi-essential ones like <link rel="canonical" href="...">7.

Now most of your plugins are broken, but in exchange, your theme has reclaimed complete control over what gets sent to the user. You can select what content you actually want delivered, and deliver no more than that. It’s harder work for you, but your site becomes so much lighter.

Animated GIF from The Simpsons. Leonard Nimoy says "Well, my work is done here." Barney says "What do you mean? You didn't do anything?" Nimoy laughs and replies "Didn't I?" before disappearing as if transported away by a Star Trek teleporter.
Your site is faster now. It doesn’t work, but it’s quick about it!

2. Throw away 100% of your render-blocking JavaScript (and as much as you can of the rest)

The single biggest bottleneck to the user viewing a modern WordPress website is the JavaScript that needs to be downloaded, compiled, and executed before the page can be rendered. Most of that’s plugins, but even on a nearly-vanilla installation you might find a copy of jQuery (eww!) and some other files.

In step 1 you threw it all away, which is great… but I’m betting you were depending on some of that to make your site work? Let’s put it back, carefully and selectively, while minimising the impact on load time.

That means scripts should be loaded (a) low-down, and/or (b) marked defer (or, better yet, async), so they don’t block page rendering.

If you haven’t already, you might like to View Source on this page. Count my <script> tags. You’ll probably find just two of them: one external file marked async, and a second block right at the bottom.

Screenshot showing source code of <script> tags on danq.me. There's one <script async> that loads instant.js, and an inline script with three sections: one that adds Web Share API functionality, one that manages VR360 images, and one that loads a service worker.
The only third-party script routinely loaded on danq.me is Instant.Page, which specifically exists to improve perceived performance. It preloads links when you hover over or start-to-touch them.

The inline <script> in my footer.php wraps a single line of PHP: which looks a little like this: <?php echo implode("\n\n", apply_filters( 'danq_footer_js', [] ) ); ?>. For each item in an initially-empty array, it appends to the script tag. When I render anything that requires JavaScript, e.g. for 360° photography, I can just add to that (keyed, to prevent duplicates when viewing an archive page) array. Thus, the relevant script gets added exclusively to the pages where it’s needed, not to the entire site.

The only inline script added to every page loads my service worker, which itself aims to optimise caching as well as providing limited “offline” functionality.

While you’re tweaking your JavaScript anyway, you might like to check that any suitable addEventListeners are set to passive mode. Especially if you’re doing anything with touch or mousewheel events, you can often increase the perceived performance of these interactions by not letting your custom code block the default browser behaviour.

I promise you; most of your blog’s front-end JavaScript is either (a) garbage nobody wants, (b) polyfills for platforms nobody uses, or (c) huge libraries you’ve imported so you can use just one or two functions form them. Trash them.

3. Don’t use a CDN

Wait, what? That’s the opposite of what everybody else recommends. To understand why, you have to think about why people recommend a CDN in the first place. Their reasons are usually threefold:

  1. Proximity
    Claim:
    A CDN delivers content geographically-closer to the user.
    Retort:
    Often true. But in step 4 we’re going to make sure that everything critical comes within the first TCP sliding window anyway, so there’s little benefit, and there’s a cost to that extra DNS lookup and fresh handshake. Edge caching your own content may have value, but for most sites it’ll have a much smaller impact than almost everything else on this list.
  2. Precaching
    Claim:
    A CDN improves the chance resources are precached in the user’s browser.
    Retort: Possibly true, especially with fonts (although see step 6) but less than you’d think with JS libraries because there are so many different versions/hosts of each. Yours may well be the only site in the user’s circuit that uses a particular one!
  3. Power
    Claim: A CDN has more resources than you and so can better-withstand spikes of traffic.
    Retort: Maybe, but they also introduce an additional single-point-of-failure. CDNs aren’t magically immune to downtime nor content-blocking, and if you depend on one you’ve just doubled the number of potential failure points that can make your site instantly useless. Furthermore: in exchange for those resources you’re trading away your users’ privacy and security: if a CDN gets hacked, every site that uses it gets hacked too.

Consider edge-caching your own content only if you think you need it, but ditch jsDeliver, cdnjs, Google Hosted Libraries etc.

Screenshot showing a waterfall representation of downloading and rendering the danq.me homepage. DCL (Dom Content Loaded) occurs at 20.62ms.
Despite having no edge cache and being hosted in a different country to me, I can open a completely fresh browser and reach DOMContentLoaded on the my homepage in ~20ms. You should learn how to read a waterfall performance chart just so you can enjoy how “flat” mine is.

Hell: if you can, ditch all JavaScript served from third-parties and slap a Content-Security-Policy: script-src 'self' header on your domain to dramatically reduce the entire attack surface of your site!8

4. Reduce your HTML and CSS size to <12kb compressed

There’s a magic number you need to know: 12kb. Because of some complicated but fascinating maths (and depending on how your hosting is configured), it can be significantly faster to initially load a web resource of up to 12kb than it is to load one of, say, 15kb. Also, for the same reason, loading a web resource of much less than 12kb might not be significantly faster than loading one only a little less than 12kb.

Exploit this by:

  1. Making your pages as light as possible9, then
  2. Inlining as much essential content as possible (CSS, SVGs, JavaScript etc.) to bring you back up to close-to that magic number again!
$ curl --compressed -so /dev/null -w "%{size_download}\n" https://danq.me/
10416
Note that this is the compressed, over-the-wire size. Last I checked, my homepage weighed-in at about 10.4kb compressed, which includes the entirety of its HTML and CSS, most of its JS, and a couple of its SVG images.

Again, this probably flies in the face of everything you were taught about performance. I’m sure you were told that you should <link> to your stylesheets so that they can be cached across page loads. But it turns out that if you can make your HTML and CSS small enough, the opposite is true and you should inline the stylesheet again: caching styles becomes almost irrelevant if you get all the content in a single round-trip anyway!

For extra credit, consider optimising your homepage’s CSS so it’s even smaller by excluding directives that only apply to non-homepage pages, and vice-versa. Assuming you’re using a preprocessor, this shouldn’t be too hard: at simplest, you can have a homepage.css and main.css, each derived from a set of source files some of which they share (reset/normalisation, typography, colours, whatever) and the rest which is specific only to that part of the site.

Most web pages should fit entirely onto a floppy disk. This one doesn’t, mostly because of all the Simpsons clips, but most should.

Can’t manage to get your HTML and CSS down below the magic number? Then at least ensure that your HTML alone weighs in at <12kb compressed and you’ll still get some of the benefits. If you’ve got the headroom, you can selectively include a <style> block containing only the most-crucial CSS, with a particular focus on any that results in layout shifts (e.g. anything that specifies the height: of otherwise dynamically-sized block elements, or that declares an element position: absolute or position: fixed). These kinds of changes are relatively computationally-expensive because they cause content to re-flow, so provide hints as soon as possible so that the browser can accommodate for them.

5. Make the first load awesome

We don’t really talk about content being “above the fold” like we used to, because the modern Web has such a diverse array of screen sizes and resolutions that doing so doesn’t make much sense.

But if loading your full page is still going to take multiple HTTP requests (scripts, images, fonts, whatever), you should still try to deliver the maximum possible value in the first round-trip. That means:

  • Making sure all your textual content loads immediately! Unless you’re delivering a huge amount of text, there’s absolutely no excuse for lazy-loading text: it’s usually tiny, compresses well, and it’s fast to parse. It’s also the most-important content of most pages. Get it delivered to the browser so it can be rendered rightaway.
  • Lazy-loading images that are “expected” to be below the fold, using the proper HTML mechanism for this (never a JavaScript approach).
  • Reserving space for blocks by sizing images appropriately, e.g. using <img width="..." height="..." ...> or having them load as a background with background-size: cover or contain in a block sized with CSS delivered in the initial payload. This reduces layout shift, which mitigates the need for computationally-expensive content reflows.
  • If possible (see point 4), move vector images that support basic site functionality, like logos, inline. This might also apply to icons, if they’re “as important” as text content.
  • Marking everything up with standard semantic HTML. There’s a trend for component-driven design to go much too far, resulting in JavaScript components being used in place of standard elements like links, buttons, and images, resulting in highly-fragile websites: when those scripts fail (or are very slow to load), the page becomes unusable.
Screenshot of danq.me's homepage with all external resources and all CSS disabled. It's plain-text, but it's still entirely useable.
If you want to be sure you’re prioritising your content first and foremost, try disabling all CSS, JavaScript, and external resources (or just access your site in a browser that ignores those things, like Lynx), and check that it’s still usable. As a bonus, this helps you check for several accessibility issues.

6. Reduce your dependence on downloaded fonts

Fonts are lovely and can be an important part of your brand identity, but they can also add a lot of weight to your web pages.

If you’re ready and able to drop your webfonts and appreciate the beauty and flexibility of a system font stack (I get it: I’m not there quite yet!), you can at least make smarter use of your fonts:

  • Every modern browser supports WOFF2, so you can ditch those chunky old formats you’re clinging onto.
  • If you’re only using the Latin alphabet, minify your fonts further by dropping the characters you don’t need: tools like Google Webfonts Helper can help with this, as well as making it easier to selfhost fonts from the most-popular library (is a smart idea for the reasons described under point 3, above!). There are tools available to further minify fonts if e.g. you only need the capital letters for your title font or something.
      • Browsers are pretty clever and will work-around it if you make a mistake. Didn’t include an emoji or some obscure mathematical symbol, and then accidentally used them in a post? Browsers will switch to a system font that can fill in the gap, for you.
  • Make the most-liberal use of the font-display: CSS directive that you can tolerate!
    • Don’t use font-display: block, which is functionally the default in most browsers, unless you absolutely have to.
    • font-display: fallback is good if you’re too cowardly/think your font is too important for you to try font-display: optional.
    • font-display: optional is an excellent choice for body text: if the browser thinks it’s worthwhile to download the font (it might choose not to if the operating system indicates that it’s using a metered or low-bandwidth connection, for example), it’ll try to download it, but it won’t let doing so slow things down too much and it’ll fall-back to whatever backup (system) font you specify.
    • font-display: swap is also worth considering: this will render any text immediately, even if the right font hasn’t downloaded yet, with no blocking time whatsoever, and then swap it for the right font when it appears. It’s probably better for headings, because large paragraphs of text can be a little disorienting if they change font while a user is looking at them!
If writing is for nerds, then typography must be doubly-so. But you’ve read this far, so I’m confident that you qualify…

7. Cache pre-compressed static files

It’s possible that by this point you’re saying “if I had to do this much work, I might as well just use a static site generator”. Well good news: that’s what you’re about to do!

Obviously you should make sure all your regular caching improvements (appropriate HTTP headers for caching, a service worker that further improves on that logic based on your content’s update schedule, etc.) first. Again: everything in this guide presupposes that you’ve already done the things that normal people do.

By aggressively caching pre-compressed copies of all your pages, you’re effectively getting the best of both worlds: a website that, for anonymous visitors, is served directly from .html.gz files on a hard disk or even straight from RAM in memcached10, but which still maintains all the necessary server-side interactivity to allow it to be used as a conventional Web-based CMS (including accepting comments if that’s your jam).

WP Super Cache can do the heavy lifting for you for a filesystem-based solution so long as you put it into “Expert” mode and amending your webserver configuration. I’m using Nginx, so I needed a try_files directive like this:

location / {
  try_files /wp-content/cache/supercache/$http_host/$wp_super_cache_path/index-https.html $uri $uri/ /index.php?$args;
}

8. Optimise image formats

I’m sure your favourite performance testing tool has already complained at you about your failure to use the best formats possible when serving images to your users. But how can you fix it?

There are some great plugins for improving your images automatically and/or in bulk – I use EWWW Image Optimizer – but to really make the most of them you’ll want to reconfigure your webserver to detect clients that Accept: image/webp and attempt to dynamically serve them .webp variants, for example. Or if you’re ready to give up on legacy formats and replace all your .pngs with .webps, that’s probably fine too!

Image containing the text
The image you see at https://danq.me/_q23u/2023/11/dynamic.png is probably an image/webp. But if your browser doesn’t support WebP, you’ll get an image/png instead!

Assuming you’ve got curl and Imagemagick‘s identify, you can see this in action:

  • curl -s https://danq.me/_q23u/2023/11/dynamic.png -H "Accept: image/webp" | identify -
    (Will give you a WebP image)
  • curl -s https://danq.me/_q23u/2023/11/dynamic.png -H "Accept: image/png" | identify -
    (Will give you a PNG image, even though the URL is the same)

9. Simplify, simplify, simplify

The single biggest impact you can have upon the performance of your WordPress pages is to make them less complex.

I’m not necessarily saying that everybody should follow in my lead and co-publish their WordPress sites on the Gemini protocol. But you’ve got to admit: the simplicity of the Gemini protocol and the associated Gemtext format makes both lightning fast.

Screenshot showing this blog post as viewed via Gemini, in the Lagrange browser.
You don’t have to go as light as Gemtext – like this page on Gemini does – to see benefits.

Writing my templates and posts so that they’re compatible with CapsulePress helps keep my code necessarily-simple. You don’t have to do that, though, but you should be asking yourself:

  • Does my DOM need to cascade so deeply? Could I achieve the same with less?
  • Am I pre-emptively creating content, e.g. adding a hidden <dialog> directly to the markup in the anticipation that it might be triggered later using JavaScript, rather than having that JavaScript run document.createElement the element after the page becomes readable?
  • Have I created unnecessarily-long chains of CSS selectors11 when what I really want is a simple class name, or perhaps even a semantic element name?

10. Add a Service Worker

A service worker isn’t magic. In particular, it can’t help you with those new visitors hitting your site for the first time12.

A service worker lets you do smart things on behalf of the user’s network connection, so that by the time they ask for a resource, you already fetched it for them.

But a suitable service worker can do a few things that can help with performance. In particular, you might consider:

  • Precaching assets that you anticipate they’re likely to need (e.g. if you use different stylesheets for the homepage and other pages, you can preload both so no matter where a user lands they’ve already got the CSS they’ll need for the entire site).
  • Preloading popular pages like the homepage and recent articles, allowing them to load quickly.
  • Caching a fallback pages – and other resources as-they’re-accessed – to support a full experience for users even if they (or your site!) disconnect from the Internet (or even embedding “save for offline” functionality!).

Chapters 7 and 8 of Going Offline by Jeremy Keith are especially good for explaining how this can be achieved, and it’s all much easier than everything else I just described.

Anything else?

Did I miss anything? If you’ve got a tip about ramping up WordPress performance that isn’t one of the “typical seven” – probably because it’s too hard to be worthwhile for most people – I’d love to hear it!

Footnotes

1 You’ll sometimes see guides that suggest that using a CDN is to be recommended specifically because it splits your assets among multiple domains/subdomains, which mitigates browsers’ limitation on the number of files they can download simultaneously. This is terrible advice, because such limitations essentially don’t exist any more, but DNS lookups and TLS handshakes still have a bandwidth and computational cost. There are good things about CDNs, sometimes, but this has not been one of them for some time now.

2 I’m not sure why guides keep stressing the importance of minifying code, because by the time you’re compressing them too it’s almost pointless. I guess it’s helpful if your compression fails?

3 “Use a faster server” is a “just throw money/the environment at it” solution. I’d like to think we can do better.

4 For my personal blog, I choose to prioritise user experience, privacy, accessibility, resilience, and standards compliance above almost everything else.

5 If you prefer to keep your backstab code separate, you can put it in a custom plugin, but you might find that you have to name it something late in the alphabet – I’ve previously used names like zzz-danq-anti-plugin-hacks – to ensure that they load after the plugins whose functionality you intend to unhook: broadly-speaking, WordPress loads plugins in alphabetical order.

6 I’ve assumed you’re using a classic, not block, theme. If you’re using a block theme, you get a whole different set of performance challenges to think about. Don’t get me wrong: I love block themes and think they’re a great way to put more people in control of their site’s design! But if you’re at the point where you’re comfortable digging this deep into your site’s PHP code, you probably don’t need that feature anyway, right?

7 WordPress is really good at serving functionally-duplicate content, so search engines appreciate it if you declare a proper canonical URL.

8 Before you choose to block all third-party JavaScript, you might have to whitelist Google Analytics if you’re the kind of person who doesn’t mind selling their visitor data to the world’s biggest harvester of personal information in exchange for some pretty graphs. I’m not that kind of person.

9 You were looking to join me in 512kb club anyway, right?

10 I’ve experimented with mounting a ramdisk and storing the WP Super Cache directory there, but it didn’t make a huge difference, probably because my files are so small that the parse/render time on the browser side dominates the total cascade, and they’re already being served from an SSD. I imagine in my case memcached would provide similarly-small benefits.

11 I really love the power of CSS preprocessors like Sass, but they do make it deceptively easy to create many more – and longer – selectors than you intended in your final compiled stylesheet.

12 Tools like Lighthouse usually simulate first-time visitors, which can be a little unfair to sites with great performance for established visitors. But everybody is a first-time visitor at least once (and probably more times, as caches expire or are cleared), so they’re still a metric you should consider.

Screenshot of a code editor showing a typical WordPress theme's header.php, but with the wp_head() line commented out.× Animated GIF from The Simpsons. Leonard Nimoy says "Well, my work is done here." Barney says "What do you mean? You didn't do anything?" Nimoy laughs and replies "Didn't I?" before disappearing as if transported away by a Star Trek teleporter.× Screenshot showing source code of <script> tags on danq.me. There's one <script async> that loads instant.js, and an inline script with three sections: one that adds Web Share API functionality, one that manages VR360 images, and one that loads a service worker.× Screenshot showing a waterfall representation of downloading and rendering the danq.me homepage. DCL (Dom Content Loaded) occurs at 20.62ms.× Screenshot of danq.me's homepage with all external resources and all CSS disabled. It's plain-text, but it's still entirely useable.× Screenshot showing this blog post as viewed via Gemini, in the Lagrange browser.×

Incredible Doom

I just finished reading Incredible Doom volumes 1 and 2, by Matthew Bogart and Jesse Holden, and man… that was a heartwarming and nostalgic tale!

Softcover bound copies of volumes 1 and 2 of Incredible Doom, on a wooden surface.
Conveniently just-over-A5 sized, each of the two volumes is light enough to read in bed without uncomfortably clonking yourself in the face.

Set in the early-to-mid-1990s world in which the BBS is still alive and kicking, and the Internet’s gaining traction but still lacks the “killer app” that will someday be the Web (which is still new and not widely-available), the story follows a handful of teenagers trying to find their place in the world. Meeting one another in the 90s explosion of cyberspace, they find online communities that provide connections that they’re unable to make out in meatspace.

A "Geek Code Block", printed in a dot-matrix style font, light-blue on black, reads: GU D-- -P+ C+L? U E M+ S-/+ N--- H-- F--(+) !G W++ T R? X?
I loved some of the contemporary nerdy references, like the fact that each chapter page sports the “Geek Code” of the character upon which that chapter focusses.1
So yeah: the whole thing feels like a trip back into the naivety of the online world of the last millenium, where small, disparate (and often local) communities flourished and early netiquette found its feet. Reading Incredible Doom provides the same kind of nostalgia as, say, an afternoon spent on textfiles.com. But it’s got more than that, too.
Partial scan from a page of Incredible Doom, showing a character typing about "needing a solution", with fragments of an IRC chat room visible in background panels.
The user interfaces of IRC, Pine, ASCII-art-laden BBS menus etc. are all produced with a good eye for accuracy, but don’t be fooled: this is a story about humans, not computers. My 9-year-old loved it too, and she’s never even heard of IRC (I hope!).

It touches on experiences of 90s cyberspace that, for many of us, were very definitely real. And while my online “scene” at around the time that the story is set might have been different from that of the protagonists, there’s enough of an overlap that it felt startlingly real and believable. The online world in which I – like the characters in the story – hung out… but which occupied a strange limbo-space: both anonymous and separate from the real world but also interpersonal and authentic; a frontier in which we were still working out the rules but within which we still found common bonds and ideals.

A humorous comic scene from Incredible Doom in which a male character wearing glasses walks with a female character he's recently met and is somewhat intimidated by, playing-out in his mind the possibility that she might be about to stab him. Or kiss him. Or kiss him THEN stab him.
Having had times in the 90s that I met up offline with relative strangers whom I first met online, I can confirm that… yeah, the fear is real!

Anyway, this is all a long-winded way of saying that Incredible Doom is a lot of fun and if it sounds like your cup of tea, you should read it.

Also: shortly after putting the second volume down, I ended up updating my Geek Code for the first time in… ooh, well over a decade. The standards have moved on a little (not entirely in a good way, I feel; also they’ve diverged somewhat), but here’s my attempt:

----- BEGIN GEEK CODE VERSION 6.0 -----
GCS^$/SS^/FS^>AT A++ B+:+:_:+:_ C-(--) D:+ CM+++ MW+++>++
ULD++ MC+ LRu+>++/js+/php+/sql+/bash/go/j/P/py-/!vb PGP++
G:Dan-Q E H+ PS++ PE++ TBG/FF+/RM+ RPG++ BK+>++ K!D/X+ R@ he/him!
----- END GEEK CODE VERSION 6.0 -----

Footnotes

1 I was amazed to discover that I could still remember most of my Geek Code syntax and only had to look up a few components to refresh my memory.

Softcover bound copies of volumes 1 and 2 of Incredible Doom, on a wooden surface.× A "Geek Code Block", printed in a dot-matrix style font, light-blue on black, reads: GU D-- -P+ C+L? U E M+ S-/+ N--- H-- F--(+) !G W++ T R? X?× Partial scan from a page of Incredible Doom, showing a character typing about "needing a solution", with fragments of an IRC chat room visible in background panels.× A humorous comic scene from Incredible Doom in which a male character wearing glasses walks with a female character he's recently met and is somewhat intimidated by, playing-out in his mind the possibility that she might be about to stab him. Or kiss him. Or kiss him THEN stab him.×