Manu Sporny: So I've got an exciting announcement let me go ahead and share my screen really quickly I can find it so the state of California has just released a very big pilot to California residents using verifiable credentials. ✪

Manu Sporny: And decentralized identifiers so this is the California DMV app the California DMV app allows you to hold mobile driver's licenses and it also lets you do digital age verification specifically it uses the true age program which uses verifiable credentials decentralized identifiers and data integrity and a bunch of other stuff that we're standardizing it w3c. ✪

Manu Sporny: This is a. ✪

Manu Sporny: Because the pilot includes 1.5 million people in the state of California this is a huge deployment of w3c Technology verifiable credentials this image you see over here on the left here that QR code is a verifiable credential it's a w3c encoded digitally signed verifiable credential using technologies that all of us here have been working on for many many years the. ✪

Manu Sporny: https://www.nbclosangeles.com/news/local/california-mobile-drivers-license-pilot-program/3216602/ ✪

Manu Sporny: That's huge right because because they're going to start out with the population of 1.5 million people and they're going to grow it to 24 million people anyone that drives in the state of California or has driver's license will have the ability to deliver verifiable credentials through the kaltura media be hap so that's item one that's you know a big huge pilot you can read more about it actually here let me go ahead and drop the links here into the chat Channel. ✪

Manu Sporny: You can read more about it. ✪

Manu Sporny: https://www.dmv.ca.gov/portal/ca-dmv-wallet/truage/ ✪

Manu Sporny: For Nia DMV webpage where they cover the true age program the true age program the other big news here is with the announcement that the California DMV app is live true age is also announcing that you know they are very much into production deployment at this point in fact true age has been in production since January of this year. ✪

Manu Sporny: But we were waiting on. ✪

Manu Sporny: The California announcement to note that so everyone in this you know this is a this is a huge kind of watershed moment I think for people in this community this is you know in production deployed real citizens are using it the true age program uses a very aggressive privacy stance meaning there's no personally identifiable information in the verifiable credential it's tokenized single use tokens much. ✪

Manu Sporny: Better than. ✪

Manu Sporny: This license which has 35 pieces of pii so there we go that's the announcement for this week. ✪

Manu Sporny: Yes so California is the first state to basically go we're just going to support multiple formats so there's support mdl and that's that you use that if you want to board an airplane and they support verifiable credentials for the age verification portion of this. ✪

Manu Sporny: Yeah so they're dual sorry they're very much multi multi issuance at this point they're basically saying we don't know which one of these formats are going to win in the end and we're just going to support all of them and and it's you know and it's possible to do so this is a example of it. ✪

Manu Sporny: Yeah well both issue right so the issuer's here interesting the the California DMV wallet is the wallet it's an app but it's got multiple issuers associated with State of California and then the National Association of convenience stores retailers that that Association issues the age credential so this is also an example of like multi-source credentials from a variety of different places being put into the. ✪

Manu Sporny: Wallet in being used for. ✪

Manu Sporny: So the the wallet is something that Spruce so you know when changing X chair for this group is the CEO of spruce so bringing Wayne in to talk about it would be good and then the true age folks that's us so we built architect and deployed the true age system in that's digital bizarre so we deployed that architecture in the in the u.s. so yeah happy too happy to chat more about it we should definitely have Wayne and them coming. ✪

Manu Sporny: And talk about it as well. ✪

Kaliya Young: We've got the internet identity Workshop coming up in two weeks on the morning of Monday There's a open Wallet Foundation event for developers and anyone can come but it's oriented towards developers I did post a link to the list but I will repost it here it's from 9 to noon. ✪

Kaliya Young: A tiger. ✪

Kaliya Young: Herman location but we'll figure that out and I also wanted to say I'm going to be at identity week America next week in DC and I actually have free tickets to give away if you want a free ticket if you're in the area or nearby I'm happy to send you a link to register if you want a back Channel me. ✪

Manu Sporny: Yeah I guess I don't know if anyone's got a report out from what happened at the w3c technical plenary two weeks ago but there is the other the other really interesting thing is that there was very heavy interest by the browser manufacturers Apple and Google in Microsoft's browser team and the Android Team all met up at the w3c technical plan area to talk about. ✪

Manu Sporny: How does. ✪

Manu Sporny: W3c verifiable credentials in Mobile driver's licenses through a browser API so this is all about you know open Wallet selection and invocation there some proposals that are kind of flying around from one you know one of them's from Apple the other ones from Google but the the outcome of those discussions was really positive in that the Google Chrome team at least has stated that there. ✪

Manu Sporny: Very interested in providing. ✪

Manu Sporny: Open Wallet selection in the web browser to deliver things like you know mobile driver's licenses or verifiable credentials they want to stay format agnostic protocol agnostic it's still a bit you know an active discussion you know whether or not the support both native apps and web apps is a you know as a part of the discussion but I mean they were like you know 3036 browser. ✪

Manu Sporny: Core people in the. ✪

Manu Sporny: You had program managers from Google and Android for Google Chrome and Android you know in Apple's browser in attendance so they are following and of course a number of us in this community have been talking with them directly they are following some of this stuff some of the groundwork that was laid with the credential Handler API chappie but they're also looking for inspiration from. ✪

Manu Sporny: Um you know the. ✪

Manu Sporny: Double driver's license stuff that Apple's been doing and the web payment stuff that has been done in the past so this is another kind of big movement where the browser vendors have kind of woken up and gone oh we need to be a part of this there now weekly meetings in the web incubator community group so this is another w3c community group called ycg that is usually where the browser vendors test. ✪

Manu Sporny: Test test. ✪

Manu Sporny: Is before they try to create working groups at w3c on it there is a plan for something called An Origin trial in the Google Chrome browser starting in probably about five months and An Origin trial in Google Chrome is where they build functionality in an only allowed to be accessed by certain you know people certain demographics or they hide it behind the browser invocation. ✪

Manu Sporny: Russian flag but at that. ✪

Manu Sporny: You know they have real running code able to move things like mobile driver's licenses and verifiable credentials they run those with the intent purpose of shutting them down but you know they run them to get like real world data back on how people are going to use the API and things of that nature so a number of us in this community are going to participate in that origin trial to ensure that at least the ccgs some of the ccgs in. ✪

Manu Sporny: Tourists are you know represented there. ✪

Manu Sporny: The verifiable credentials working groups interests are represented there that's it for that item. ✪

Anil John: Just if folks have not seen it I think there is a announcement from the open ID Foundation that they released a new white paper called human-centric digital identity for government officials I happened to read that and I found it to be really worthwhile read I think there's a lot of work that went into creating the paper getting a dip variety of different perspectives I. ✪

Anil John: No folks. ✪

Anil John: https://openid.net/human-centric-digital-identity-whitepaper/ ✪

Anil John: Dave Birch and many others in the community actively contribute to that paper so I would highly recommend reading it I found it to be really interesting and a very holistic look at the current state of identity across the globe and a very worthwhile read so I highly recommend I'll put a link in the chat for where people can find it. ✪

Manu Sporny: Awesome thank you Harrison let me go ahead and share my screen going to slide show mode can folks see that. ✪

Manu Sporny: Okay yeah thank you Harrison for inviting us to speak I've also got Dave Longley here who did an enormous amount of the technical work on this selective disclosure mechanism this approach for data Integrity just to give folks a bit of a background who might not know so the you know we are a part of the credentials community group here at the World Wide Web Consortium we incubate. ✪

Manu Sporny: Here in once we feel like that technology is ready to go standards track it w3c we kind of push it onto you know we work on a charter we push the technology kind of into an official working group at w3c most recently the the latest working group that we had a part meaning the credentials community group had a part in creating was the second iteration of the w3c verifiable. ✪

Manu Sporny: Churchill's working group. ✪

Manu Sporny: Um in scope for that working group were a couple of items the the first one was you know maintain verifiable credentials release a 20 version of it you know make it better that kind of thing and the other work item that went along with it was securing mechanisms for verifiable credentials so everyone knows the the verifiable credential the thing that makes it verifiable is that you've got some. ✪

Manu Sporny: Kind of digital signature on it some kind of digital. ✪

Manu Sporny: Tells you who signed it who issued it who's making those statements so securing mechanisms were in scope and there are multiple ways of doing it there's the besiege odd stuff there's the SD jot stuff in there's a mechanism called Data Integrity so we're going to be looking at that data Integrity approach today and so and so all this to say that this is work that is actively being. ✪

Manu Sporny: Sized at w3c. ✪

Manu Sporny: See in an official working group feel free to interrupt at any point here I will definitely stop at certain points through here and see if there any questions the talk is this is largely kind of like a high-level introduction to selective disclosure with a very strong focus on specific mechanism but you know. ✪

Manu Sporny: For any form of selective disclosure I think is fair game to discuss here so if you have any questions on any of that stuff you know please let us know okay so let's get started one big disclaimer here is that all I'm trying to do here is just introduce data Integrity selective disclosure schemes in provide some benefits and drawbacks this is not meant to be like a. ✪

Manu Sporny: Closure mechanism is better than your selective disclosure mechanism you know let's have a big giant argument about it this is just kind of like information sharing I stayed away from a comparison because that tends to get people's kind of hackles up so this is meant to just be a you know here's here's what we have and here's what it does and a discussion around that just the set of things that we're going to cover today. ✪

Manu Sporny: Just a really brief. ✪

Manu Sporny: View of selective disclosure and what it is go over some selected disclosure use cases look at the life cycle for Selective disclosure so you know you know there's this three-party model that we have you know which party does what when selective disclosures done you know what are the things to look out for and then we'll go on a into a how it works from a conceptual standpoint so that's going to be like a really high level like no techno jargon. ✪

Manu Sporny: Jargon anything just like. ✪

Manu Sporny: He what are we doing here how does it work and then we will go into a deep dive if we have time or if people are interested so that's kind of what we're going to cover over the next 15 to 20 minutes I think is there anything on here that folks would like to cover of that I mean it's fine if it's out of left field but it was there anything you were hoping that would be covered and you're not seeing it on on here we're going to cover it. ✪

Manu Sporny: Okay all right all right then let's get started what is selective disclosure it's a it's a super simple straightforward concept right so the idea here is that got some document some data in you're going to hand that data over to a holder so you know someone that's going to hold on to that data and you want to empower them to only reveal specific information in that document. ✪

Manu Sporny: To a verifier the. ✪

Manu Sporny: Easiest way to think about this is like you've got a driver's license and if somebody you know if you're going to go rent a car they may not need to know your everything on that driver's license right or if you're trying to and I stay away from the proving age thing because I think that's a very complex use case if all you're trying to do is share some information. ✪

Manu Sporny: This license then handing all of it over is not what you want to do you want you want a way to select a bliss to disclose what's in that driver's license so that's all selective disclosure is is we're trying to empower people to not over share information and data like they do today and that's it in a nutshell that's all it's also like the disclosure is it certainly gets more complex from there. ✪

Manu Sporny: But you know that's kind. ✪

Manu Sporny: What we're dealing with today okay so what are some use cases that we can think of you know with respect to selective disclosure one of them is proving that you're a citizen of of a particular country without revealing your address so let's say you have something like a passport or a permanent resident card you may not want to share all the information like. ✪

Manu Sporny: Like what. ✪

Manu Sporny: Three was your height and weights or that kind of stuff if all you need to do is prove that you are a citizen of a particular country. ✪

Manu Sporny: Another use case is proving that you're an employee of a particular company without revealing your name and position so you know saying that you are an employee of Utopia Corp instead of revealing that you have a very sensitive position in that organization is a desirable thing to do if you have an employee ID card but you know selective disclosure does not. ✪

Manu Sporny: Apply to people or identity documents for people if you think of shipping manifests like the contents of a shipment so let's say that you need to you have a shipment and you need to reveal where the shipment is going without revealing the context contents of the shipment so and that has a you know pretty direct analogy to the way. ✪

Manu Sporny: Shipping or. ✪

Manu Sporny: You put an address on the outside of the of the of the package in whoever shipping it really doesn't see inside the Box they just send it to where it's going right so if we want to take that thing digital but use you know a single document selective disclosure helps their if we look at payments revealing the sender and receiver of a payment to make sure that they're not on the sanction list. ✪

Manu Sporny: Or something of that nature. ✪

Manu Sporny: Feeling exactly what's being paid for so sending and receiving payment without understanding you know what the goods that are being exchanged our are you know is another legitimate selective disclosure use case and then of course this this proving that you're over a certain age and are licensed to drive without sharing your Pi I so the use case here is like a car rental or temporary car rental or even golf cart rental. ✪

Manu Sporny: You know. ✪

Manu Sporny: Was that you can operate over a certain age and all you really need to do is prove that you are a license to operate the motor vehicle Without Really revealing anything else so these are you know some fairly straightforward examples of selective disclosure again what we're trying to do is protect protect people's privacy and it's not just people right it's protect people's privacy. ✪

Manu Sporny: To see protect an. ✪

Manu Sporny: To see when they're interacting in a transaction Christopher Allen had or had this you know interesting thing about Progressive disclosure the idea here being that you know when you start out in a transaction you probably want to share the absolute minimum necessary to get to the next level with you know more and more disclosure happening as you feel more and more comfortable. ✪

Manu Sporny: Edible with the entity that your. ✪

Manu Sporny: Acting with there are also just you know I know everyone in this community like understands like gdpr and the Privacy you know California consumer Privacy Act and all that kind of stuff there's regulation now that is pushing organizations to collect less and less information to only collect the information that is necessary for the transaction you know if regulations require the collection of certain information. ✪

Manu Sporny: Don't over collect information so selective disclosure helps with all those use cases did I miss a use case that folks are interested in is there. ✪

Manu Sporny: Do you disagree with any of these use cases hold for a couple of beats. ✪

Manu Sporny: That you're in the queue. ✪

Manu Sporny: Yeah absolutely yeah that's that's that's yeah that's a great that's a great point the other thing I that is somewhat related to that that's come up in the past is use use of data for you know training AI which is you know it's a touchy it's a touchy subject right now right I mean nobody wants to have their data be used to train an AI without their consent and even then you may want to only selectively disclosed some parts of what. ✪

Manu Sporny: R doing or you might want to Blind. ✪

Manu Sporny: The data that you're sending over entirely to make sure that only the only the data that you want to you know be used to train it is being used so research studies and in sharing of information certainly. ✪

Manu Sporny: Any other use cases that folks. ✪

Manu Sporny: All right I'm going to I'm going to go on but yeah this is so hopefully this gives you know everyone in understanding of like why why people are so interested in selective disclosure it's not you know who cool whiz-bang you know new technology cryptography its data privacy regulation I think is driving a lot of this stuff and people are starting to understand how their data is being used and don't necessarily like like how it's being used in many cases. ✪

Manu Sporny: Okay so how does Selective disclosure work with verifiable credentials this is this three-party model that we keep talking about and have worked on for many years standardized you've got an issue or a holder and a verifier the issue or issues of verifiable credential to a holder who then stores that in like a digital wallet and then they go to another party with some which is a verifier who asks for some variation of that information. ✪

Manu Sporny: From the issue. ✪

Manu Sporny: And then the whole represents something to the verifier so the using selective disclosure doesn't change that model at all and it doesn't change the flow of information at all the only difference largely is in the cryptography that is used to secure the verifiable credential the issuer has to knowingly use a selective disclosure scheme when they handed over to the holder the holder then sees that the issuer has given. ✪

Manu Sporny: Them something that they can. ✪

Manu Sporny: It's close and so when the verifier requests something the verifier also has to request it in a way that says I am okay with a selective disclosure selectively disclosed a piece of information that thing to understand here is that the issuer in the verifier have to buy into this ecosystem and that can be challenging right sometimes issuers are unknown you know they don't know any better and they just. ✪

Manu Sporny: Issue a base. ✪

Manu Sporny: Thing sometimes they can't you know don't have the technological capabilities to issue a verifiable credential as a selectively disclosed thing and sometimes the verifier and this is what people are you know a bit concerned about and this is why we're you know doing work on trust Frameworks and verifiable verifiers sometimes the verifier won't give you the option they'll say no I want all this information I'm do. ✪

Manu Sporny: Don't support selective disclosure. ✪

Manu Sporny: That's the thing to keep in mind here is that it will require a good bit of pressure on issuers and verifiers to make sure that they do the right thing in largely again regulation is driving a lot of that you know the consumer privacy acts gdpr is is trying to really put pressure on organizations to. ✪

Manu Sporny: Do the right thing and. ✪

Manu Sporny: Like more than what you need Okay so let's see I'm going to yeah there was a performance slide in here I've taken that out just because that raises people's hackles let's start talking about data integrity and selected disclosure specifically the the scheme that's being worked on in the verifiable credential working group there were a couple of requirements there one of them is we had to provide a mechanism that supported nist approved cryptography so there's. ✪

Manu Sporny: Other selective disclosure mechanisms like BBS that is not recognized directly by nist and you know people don't feel like it's mature enough so if you want to really you know say hey look we're using this to prove cryptography. This selective disclosure mechanism for data Integrity is something we wanted to we we needed to be able to say that right so that governments could adopt. ✪

Manu Sporny: Up this. ✪

Manu Sporny: We needed to support mandatory disclosure of specific properties so when an issue or issues something let's say that there's a revocation list associated with the credential well you shouldn't allow a holder to selectively disclosed that whether or not the credential is revoked so you from a mandatory standpoint have to disclose you know whether or not the credentials revoked or not we wanted really small initial proof sizes between 7000. ✪

Manu Sporny: 4000 Bytes to store in the digital wallet so. ✪

Manu Sporny: To make it so that you know what's stored in a digital wallet is reasonable from a proof size perspective and then for disclosure we wanted really small as small as we could get them disclosure slot sizes because there are some use cases that are data constrained in some of the selective disclosure schemes are have really big signatures so we optimized for really small disclosure proof sizes. ✪

Manu Sporny: In disclosure proof size. ✪

Manu Sporny: Let's start small so the less you share the smaller the signature size the more you share the more the signature size grows so about 128 bytes per claim that you're expressing this is an example we tried to take like what a driver's license or a permanent resident card would look like under this disclosure scheme so the lines are showing how big the signature size is. ✪

Manu Sporny: A selectively disclosed scheme so as you can see here with one claim revealed we're down at like 270 to 300 bytes and as each new claim is revealed your signature size grows but it never gets you know super crazy big or anything like that so anyway there's a you know pretty standard linear curve to how big this. ✪

Manu Sporny: Signature sizes are. ✪

Manu Sporny: Let's talk about how it works at a super high level again this is kind of the journey here the issuer has to digitally sign something using the selective disclosure scheme they handed over the holder which understands that they're holding onto a verifiable credential and selective disclosure scheme and then the verifier has to ask for a subset of that credential like I want to see your driver's license but the only thing I want to see on it is whether or not you have a driver's license at all I don't want to see the driver's license number I don't want to see you. ✪

Manu Sporny: In States but I don't want to see where you live for example and so that then there's a you know protocol where the holder selectively discloses that stuff to the verifier in the verifier can check the signature just the properties it asked for okay so how does it work let's look at a pretty simple credential this is an employee use case so this is an employee credential the employee credential is valid from June 2020 3 2 Jun. ✪

Manu Sporny: The subject is Jane Doe and Jane Doe has some information in here Jane's employee ID is this number here Jane's job title is a comptroller she works in the accounting division in her employers name is example Corporation right so this is a verifiable you can this is a verifiable credential the types of claims you'd see in a verifiable credential and we want to make this selectively disclosable so how do we do. ✪

Manu Sporny: Do that well the. ✪

Manu Sporny: Step at least with data Integrity is we canonicalize so we have to take these statements and put them in a certain order so that we know you know which field where when we reveal the certain Fields the same field you know is understood to be revealed at the verifier thing so so this green thing happening over here on the left is we have just kind of sorted the data right using you know. ✪

Manu Sporny: So that's step one is you put it in order put it in a list in order step two is you sign every single statement so you put the put the data in order and then for each line here you sign it there's a bit of a hand wave going on there you know some of these statements you're going to group together and say you must disclose these things group them all together sign them once and then you can select ones to be selectively disclosed. ✪

Manu Sporny: So for example the validity dates mandatory Lee disclosed right you want to make sure that the validity of the credential is well-known but you may want to hide their employer ID or make that selectively disclosable okay so step one is you cannot Collide Step 2 is you sign all the statements step three is you hand though that whole. ✪

Manu Sporny: Sign credential over to the holder. ✪

Manu Sporny: Receives this it's digitally signed by the issuer and they see that it's a selectively disclosable credential and then the verifier asks for specific claims so the verifier goes hey I need an employee credential from you stating your employer's name I just want to know who your employer is and whether or not you know it's current just give me that information I don't need to know your employer ID number I don't need to know your I don't even know need to know your name right so you. ✪

Manu Sporny: Can think of this as like for building access is your employer in the. ✪

Manu Sporny: You know use an employee credential guess with your employees name to get access to the building so when the holder creates this disclosure the selectively disclosed verifiable credential that's the only two things that includes in there it says this VC is an employee credential in my employers example Corporation and that's it that's all they share right so that's a that's a subset of what was originally created okay and and that's that's pretty much it. ✪

Manu Sporny: At a high-level let me pause to see if. ✪

Manu Sporny: Questions here and then we can get deep into the weeds if folks want. ✪

Manu Sporny: That's a great question so canonicalization allows us so do you need it do you need it it depends on your use case so SD jot it well it's arguable whether or not SD jot actually canonicalize has so some people will argue like it doesn't canonicalize at all and you don't need it other people will argue that it's got a canonicalization mechanism in there so so most of these schemes do some. ✪

Manu Sporny: And of canonical. ✪

Manu Sporny: And some of them are more complex than than the other the reason that we canonicalize in data Integrity is because it allows us to use the same signature when the verifiable credential is expressed in a variety of different formats so Jason versus C boar versus yeah Mille when we use canonicalization in the way that we do we can make sure that the same signature applies across multiple different data formats we. ✪

Manu Sporny: An also stack signatures one on top. ✪

Manu Sporny: We can do a signature that uses standard Miss cryptography that's not selectively disclosable and then we can add another signature that allows selective disclosure and then we can add another signature that allows unlink Bill signatures and then we could in the future add another so you had another signature that does post Quantum signatures that's a Quantum safe signature so canonicalization is this. ✪

Manu Sporny: Mechanism that we can use that gives us some advantage. ✪

Manu Sporny: With with a drawback being that it's more cannot it's more complicated to do than you know come alkalization I know that yeah go ahead go ahead. ✪

Manu Sporny: Technically it's more than that but conceptually it's not any different than that I like a canonicalizing a list and putting it in alphabetical order that's canonicalization right so if you had a bunch of items and you just sorted by where you know by alphabetical order that is an example of canonicalization and and the type of canonicalization we do. ✪

Manu Sporny: For Selective. ✪

Manu Sporny: Closure is not really all that different from from doing that. ✪

Manu Sporny: Is that is that that is really fantastic news Claire one of the things I wanted to point out here is this selective disclosure mechanism works with nist approved crypto in in we are working with the EBS as well there's a mechanism that allows this selective disclosure stuff to work with the BBS mechanism that you were talking about Claire and we're pretty excited about that as well so it's great news on the progress. ✪

Manu Sporny: There yeah that's a great question Matt the short answer to that is no that's not solving the the same issue I think that one has to do and you'll have to forgive me fire you know I am familiar with the firework but not following it closely the what one of the big big issues there was being able to just identify entities at all the that that class of problem is like decentralized identifiers uuids for specific people and entities and. ✪

Manu Sporny: Things of that. ✪

Manu Sporny: Am I misreading kind of what you were saying that. ✪

Manu Sporny: That's really interesting yeah and if you don't mind if you could send that to the mailing list I think that would be great to look at. ✪

Manu Sporny: Awesome thanks man. ✪

Manu Sporny: That's a great question I'm Paul good to good to hear you on the call so it's not I wouldn't call it an atomic credential I'd call it you know a bunch of atomic claims in your right you do need another signature to tie them all together so I can get into that here in a bit once we go through the kind of the excruciating detail part of it and kind of show you how that works there. ✪

Manu Sporny: Just to kind of respond to your question the claims subset of the claims are Atomic their single you know claims each those are the selectively disclosable B and then there's a chunk of claims that are mandatory you must always reveal these statements and then there is a signature that goes over all of it that basically digitally signs all of it. ✪

Manu Sporny: And again I'm hand-waving a bit over the details. ✪

Manu Sporny: I'll get into the details here in a bit did that at least answer your question at a high level Paul. ✪

Manu Sporny: All right are you do we have a clear Q Harrison. ✪

Manu Sporny: All right okay I'll try to run through the excruciating detail here quickly so this is a verifiable credential this is this is a version two verifiable credential it's the employee credential so we're just doing the same credential here sorry the same example in the in the conceptual example this is what the verifiable credential would look like so this is Jane Doe who has a certain employee ID number job title. ✪

Manu Sporny: Foyer is example Corporation so we take this bear verifiable credential we canonicalize it and we Bunch those statements into two sets of statements one of them are the mandatory disclosure claims up here at the top these are the things that Jane is always going to have to reveal because the issuer feels that this is must be revealed in the issuer here has basically said you must always reveal me the issuer. ✪

Manu Sporny: Verifier can't trust the PC without that and then the validity dates and then the type of credential right but your selectively disclosed claims and Paul this is where it's like every single one of these lines is a separate statement with the separate signature your selective disclosure mechanisms sorry your claims is this list here right in these are these are both canonicalize these lists are canonicalized and so we're going to sign all these mandatory disclosure claims and one blob in. ✪

Manu Sporny: And then each one of these selective disclosure claims it's going to get it so. ✪

Manu Sporny: So one signature for all the mandatory disclosure disclosure claims here at the top and then one signature / statement down here at the bottom and that allows Jane to selectively disclose each one of these items here the signature itself that we hand over to the holder has what we call a base signature and that base Signature Signs over everything else here so Paul this is the. ✪

Manu Sporny: You know the. ✪

Manu Sporny: Thing that you were I think alluding to there is an ephemeral public key that's used just to do the selective selective signatures in the ephemeral key is signed over with the base signature so this is the issuer's signature here there's an hmac key that we use to do some privacy preserving computations on blank note identifiers this is a complex topic that I'm going to not get into today but the idea here is that we. ✪

Manu Sporny: We want to. ✪

Manu Sporny: Blind some of the information in the graph so that so it doesn't reveal information like for example the number of family members that you might have the number of items in a shipment that kind of thing so that's what this hmac keys for and then there's a list of fields that you have to mandatorily disclosed so these are Jason pointers that point to specific Fields so you have to reveal the issuer the time. ✪

Manu Sporny: Up the validity. ✪

Manu Sporny: It's here and then we have a whole bunch of selective signatures so this is for each one of those claims we want to selectively sign there's a signature there for it and the final signature size using nist approved P 256 key is 643 B so pretty small and compact there when in this is what the fully signed verifiable credential with a selective disclosure scheme looks like this is the proof down here so all that information. ✪

Manu Sporny: Fashion is contained in this digital signature down here. ✪

Manu Sporny: It just looks like a standard you know verifiable credential secured using data Integrity now we go to the verifier so what does the verifier ask for when they ask for a verifiable credential so this is using verifiable presentation request query by Example The credential query that they're sending over is we need to we need you to verify your employee that's what they want and then the example query based. ✪

Manu Sporny: The type of credential they want to receive so the verifier says I want you to give me a credential and it needs to take this kind of form and we can see here is that you know they say the type has to be an employee credential you've got to have an identifier for the credential subject and employer identifier in a name and then they provide a challenge and a domain just to make sure that the thing can't be replayed what. ✪

Manu Sporny: The holder. ✪

Manu Sporny: Is then they derive a new verifiable credential with a limited set of fields so here what they're doing is they are taking that original credential which had a whole bunch of more fields in it and they're minimizing the information and they're generating a new proof this is the signature that they're generating and then they're going to send that over to the verifier and when the verifier checks this you know there's an algorithm that's. ✪

Manu Sporny: Find in a in a specification. ✪

Manu Sporny: If I were credential working group in they will check you know this information in either get a thumbs up or thumbs down on the credential so the credential that's handed over just looks like a you know minimized version with only certain Fields exposed to the verifier okay that's it for the presentation I think we've got like maybe a couple of minutes left for Q&A. ✪

Manu Sporny: No it's there's a there's verifiable presentation request which is a work item in the ccg that's using query by example but I want to be clear like the the query language is separate from the selective disclosure mechanism you could use multiple different types of query languages so you don't have to use this one this is just the one that we've implemented and used. ✪

Manu Sporny: It's not required it was a design choice and Dave you're here I don't know if you want to kind of weigh in on that. ✪

Dave Longley: So the main reason for doing that is it reduces the disclosure proof sizes by considerable amount if you use the hash based approach approach you must disclose all of the hashes every time you do a disclosure proof If you do the atomic signature approach you only disclose the signatures that you that go along with the data that you are disclosing so the sizes go down and enable use cases for when your when your data. ✪

Manu Sporny: Yeah for example like we have use cases where we have to express this stuff in like a QR code and you have to get it in you know the idea behind selective disclosure is you're trying to minimize the amount of information you're sharing so we were like well if we have to share less than five claims then we need to make sure that the signature sizes are small enough that we can fit them in a QR code or they can go over you know a single data Block in an NFC. ✪

Manu Sporny: So we were optimizing for disclosure size versus you know the other mechanism now with that said there is nothing preventing another data Integrity crypto sweet to take the approach that SD job took right so if what we want to do is the you know the route reveal of hashes approach we could fairly easily do that with with data integrity. ✪

Manu Sporny: We were just optimizing for. ✪

Manu Sporny: Or I think a different set of use cases then SD job was optimizing for did that answer your question Paul. ✪

Manu Sporny: Yes you're absolutely right there are certainly trade-offs there remember that with the SD jawed approach you always have to reveal the full signature you know as well as all the hash it's oh so this is where we get into kind of compare contrast between the two what we found out is that that you know having run some tests with SD jot your signature sizes are usually really big your veal sizes or like to k 2 4 kilobytes in size for thing. ✪

Manu Sporny: NG the size of like a driver's license and and there's. ✪

Manu Sporny: Online or that doesn't matter but they are constrained use cases that we're dealing with where that does you no matter so these things you know it's a collection of trade-offs right in certain formats optimized for certain approaches one of the other you know trade-offs with the data Integrity approach this one specifically is that you have to do multiple signatures whereas with SDG&E you'll need to do one signature in you know there are trade-offs there. ✪

Manu Sporny: Meaning that you know you have to do multiple signatures with the selected disclosure data Integrity mechanism whereas with SDG&E you don't have to and so if you you know if your HSM such you're using or expensive then their cost considerations that you might want to take into account but you know we've again done cost analysis on it and tends to be really like a rounding error doing multiple signatures versus single one. ✪

Manu Sporny: All right I know. ✪

Manu Sporny: We're at the top of the hour and fortunately I think Phil you had a you had a question no. ✪

Phil Long: Yeah but the top of the hour I was just going to ask with the holders experiences and all this. ✪

Phil Long: We can we can leave that. ✪

Manu Sporny: Yeah well you want to simplify it as much as possible until the holder that you know you're only releasing this information right there a couple of good demos that are out there of mobile wallets doing selective disclosure but you want to keep things as simple as possible for the individual tell them that you know hey you're sharing your driver's license but you're only sharing these three fields and just let them you know communicate that to them in the street. ✪

Phil Long: Got great presentation and thank you. ✪

Manu Sporny: Thanks Phil. ✪