Gregory's ServerAnd so, it is TEA TIME
Go get yourself a hot beverage. Put honey or agave in it, if you like. Dairy, or perhaps, non-dairy, if you prefer.
=== BREAK TIME! Time for tea! ===
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251 comments
 @mlemweb Thank you for corroborating my story  Okay, I am back and I am back with tea! I made "black tea with ginger" and I put some whipped honey in it. I also made tea for my spouse I am drinking out of an oversized mug from @baconandcoconut that says "I'm that person who likes to serve on open source program committees", which is not actually accurate but I do anyway I am also sad about the US House of Representatives being shitty to trans people who work there and are just trying to make it through the day I used to do data modeling contracting for the US HoR on our legal system, true story, which sends me back to a time when I did a lot of data modeling  The house should ditch men's and women's restrooms and switch to republican & democrat restrooms. A lot of data modeling I did in that time was in the W3C Verifiable Credentials group that was working on Verifiable Credentials, zcap-ld (my spec), and, oh hey, Decentralized Identifiers (DIDs, the name is not my fault) So actually I was pretty excited when I heard that Bluesky was gonna use DIDs! Back in 2017 I wrote a whitepaper: "ActivityPub: from decentralized to distributed social networks" and it also suggested using DIDs https://github.com/WebOfTrustInfo/rwot5-boston/blob/master/final-documents/activitypub-decentralized-distributed.md I no longer think DIDs are necessary to solve this, but then and now I think *decentralized identity is important* In that sense, I am really glad Bluesky is taking on decentralized identity, as a concept! And DIDs, in a way, are a good signal. But there are several problems, the first of which is: Bluesky supports two kinds of Decentralized Identifiers and they're both -- you guessed it -- centralized! Before we get there, let's talk about what the DID spec was and what DIDs are. The core DID spec is an *abstract interface* for key management which provides a way of representing keys (and some other metadata) which can be created, retrieved, and updated/rotated. So far so good... The other requirement you would expect, based on the name, is that Decentralized Identifiers are *actually decentralized*. When I got involved in DID work, that was actually the expectation of everyone. Then it was loosened. What? Why on earth?! The reason actually stems from the first centralized DID method that Bluesky supports: did:web. did:web is centralized, and kinda useless. It just works by a regex rewrite of the DID's name to an https URI and then it's retrieved. Anywhere you use did:web, you could have just used an https: URI "Now wait Christine, didn't you say earlier that the web is decentralized and open? So therefore, did:web is decentralized and open" Yeah but the naming system of the web is CENTRALIZED We use DNS and ICANN (and then we add another centralization layer with TLS/SSL CAs)! Everyone in the DID standards space KNEW that did:web was centralized, so why on earth was a centralized identifier permitted for something named "Decentralized Identifiers"? The answer is easy. did:web is easy to implement, many DID methods were not. did:web existed for test suites. I was kind of exiting that particular area of standards when this happened but colleagues will tell you that I, and some others, were deeply upset and troubled by this "Sure having a nearly no-op DID to pass the test suite is helpful but it shouldn't be labeled as a DID, people will get confused!" Confusion, on its own, is one thing. But the problem is when confusion turns into decentralization-washing. "This is going to turn into decentralization-washing!" "It's just to pass the test suite!" [... time passes ...] "Actually we like did:web now, it's a DID method everyone can implement!" And of course once the door was open to did:web, the door was open to everything! Decentralization is now no longer a requirement for DIDs. You can make a centralized DID method and call it a "Decentralized Identifier" and you're right because it implements a spec named "Decentralized identifiers" But it's ONLY EXPERTS IN DIDs WHO UNDERSTOOD THIS Most users hear "Decentralized Identifiers" and they think they know what's being delivered, the distinction between the *spec* being called that and the *mechanism used* being centralized... you have to go digging to find that out So did:web is not only useless, it misleads people about the problem domain entirely, but hey it's now the most broadly deployed DID method in the world, congrats everyone! Speaking of centralized Decentralized Identifiers, did I mention that did:plc is centralized? For that matter, where did the term did:plc come from? Early versions of "did:plc" documentation called it the "Placeholder" DID method, that's what it stands for, to motivate changing it later Well the docs no longer say that, it now says "Public Ledger of Credentials" Good backronymn, but... did:plc is centralized, and that bothers me because once again, users think something is more decentralized than it is, because they're being *told* it's decentralized The particular way in which did:plc is centralized doesn't bug me too much but once again, few users have read into this If you read the documentation of did:plc, they're actually quite upfront about did:plc's centralization being non-ideal. That's good, I appreciate that. Again, you gotta dig though, and the name misleads (which is, to be fair, the original sin of the DID Working Group) (aside: wow my eyes are getting tired from staring at my monitor while I recap of what was a 24 page blogpost, why do I do this to myself) Aside from being irritated about the name misleading, I don't mind the centralization of did:plc too much (other things, I am more concerned about, we'll get there) There's one organization that can be queried via their API that keeps a definitive list of certificate and their updates In theory, once a DID is registered with Bluesky, it cannot be altered by Bluesky, because a cryptographic update from the original key is necessary; it's a certificate chain, a good design Bluesky can refuse to share did:plc documents or their updates, but it can't manufacture updates This is pretty good tbh, it lowers the stakes a lot to have certificate chains I love certificate chains, certificate chains are great Honestly, having a centralized registry for them, it's not the best but it's not the worst (aside from that damn naming thing) However... There are some strange, strange things about did:plc that heightens the centralization concerns and, well I'm not a cryptographer, but some of my good friends are cryptographers, etc etc. I got some... reactions to what is to follow The first strange thing to me is that did:plc uses sha256 and, AFAICT, not sha256d (which is really just running sha256 again over the hash). Unless I am missing something? Am I wrong? Maybe it's not a concern because of doc parsing but it's best practice to protect against length extension attacks The next concerning thing is that did:plc truncates the hash to just *15 bytes* of entropy. I'm... again I'm not a cryptographer, but why throw away all that delicious entropy? So the did fits in 32 characters? Weird choice, and it means collisions are cheaper  @cwebber is trashing some entropy useful to provide some of the properties @soatok mentions in his post from yesterday? https://soatok.blog/2024/11/21/key-transparency-and-the-right-to-be-forgotten/  This is public information, I don't need to file a CVE to tell you about the truncation of entropy. I am, again, not a cryptographer. Maybe it's fine? I do remember the Debian short IDs fiasco tho https://gwolf.org/2016/06/stop-it-with-those-short-pgp-key-ids.html Why not hold onto all the entropy you can get? DIDs weren't meant to be seen by the user; cryptographic identifiers in general *shouldn't be*, they should be encapsulated in the UI. We'll get to UI stuff in a bit. I just don't understand this decision though, it just seems weird to me but maybe a cryptographer will tell me it's fine, actually At any rate, I continue to not understand it, maybe it's fine, but it did play a part in that "Hijacking Bluesky Identities with a Malleable Deputy" blogpost, which is fascinating and, unlike me, is written by a Real Cryptographer (TM) https://www.da.vidbuchanan.co.uk/blog/hacking-bluesky.html Good post btw One way in which the truncation shows up in that blogpost which I thought was curious is that the attack involved generating a *longer* truncated hash The fix ended up resulting in codifying the hash length: 24 characters, and no longer https://github.com/did-method-plc/did-method-plc/pull/31 There's another thing about that blogpost that caught my attention. I will just quote it: > However, there's one other factor that raises this from "a curiosity" to "a big problem": bsky.social uses the same rotationKeys for every account. > This is an eyebrow-raising decision on its own; apparently the cloud HSM product they use does billing per key, so it would be prohibitively expensive to give each user their own. (I hear they're planning on transitioning from "cloud" to on-premise hosting, so maybe they'll get the chance to give each user their own keypair then?)  Shouldn't this be 20 bytes? There are 32 characters, and each character is base32, or 5 bits. So 160 bits? Edit: nope, wrong. I don't *think* there's a huge concern over this, because while maybe you could do a birthday collision attack in 80 bits, this wouldn't really get you much and wouldn't let you take over someone else's account. For that you'd need a pre-image attack on the whole 160 bits. Edit: 120 bits pre-image, but I think the point stands? *Also not a cryptographer!!* @fontenot no because the 32 characters includes the "did:plc:" @cwebber Hey Christine, big fan of your work, but holy yapfest. World record for longest fedi thread??  @cwebber I remember reading about DIDs a few years ago, even did a Norwegian language podcast episode talking about it @cwebber I'm so glad that you continue to enjoy that mug. And I'm also grateful that you do serve on open source program committees.  @cwebber @baconandcoconut vandalize it to say "I'm that person who open source program committees" :3 @cwebber break time? :shibalaugh: I think you invented a new thing there, but understandable  @cwebber thank you for reminding me that it is TEA TIME! Took me a minute because my water boiler needed refilling... |
I can confirm, @cwebber is currently making us both tea :)