The document discusses the technical aspects of verifiable credentials (VCs) and their implementation, particularly in the context of the Covid-19 Credentials Initiative. It details the various data formats and cryptographic methods used for secure and privacy-respecting digital credentials, emphasizing the role of JSON-LD and zero-knowledge proofs in achieving selective disclosure. The initiative aims to create open standards and interoperability for vaccine credentials among public health authorities and commercial entities.

1. February 2021
Verifiable Credentials
Flavors Explained

2. Verifiable Credentials
Flavors Explained
by Kaliya Young “Identity Woman”
Ecosystems Director at Covid Credentials Initiative
Blog Post - PDF Document

3. The VCs Data Model, defined at the W3C, is a universal data format that lets any entity
express anything about another entity. It provides a common mechanism for the
interoperable implementation of digital credentials that are cryptographically secure,
tamper-evident, privacy respecting, and machine-verifiable.

4. ● JSON-LD family with LD Signatures
❖ or with BBS+ Signatures that enable Zero Knowledge
Proofs (ZKP or ZKPs)
● JSON with JSON Web Signatures, precisely in the form of
a JSON Web Token (JWT)
● ZKP with Camenisch-Lysyanskaya Signatures (ZKP-CL)

6. Data Formats for the Claims
+ Signing Mechanisms
JSON - Signed by JWT
JSON-LD - Signed with LD Signatures

7. JSON (JavaScript Object Notation).
open standard object and document format
used for data interchange and is human
readable. It consists of attribute-value pairs.
Number
○ Age 27
String: a sequence of zero or more Unicode characters.
○ firstName - “John”
Boolean: either of the values true or false
○ Is alive = true
null: an empty value, represented by the string null
○ No spouse
Array: an ordered list of zero or more values, each of which may be of any type.
○ phoneNumbers - represents an array
○ There is more than one phone number listed, so it is represented as an array
○ children - represents an empty array ●
Object: a collection of name-value pairs where the names (also called keys) are
strings. Objects are intended to represent associative arrays, where each key is unique
within an object. Objects are delimited with curly brackets and use commas to

8. What is JWT Claim?
JWT approach to determining the meaning of claim terms in credentials.
There is an IANA registry for JWT claims as a first place to look for JWT claim
definitions.
If the claim name isn’t in the IANA register, then the claim can be given a “give it a
public name (i.e., a URI), [or] a local name (i.e., any string)”. The meaning of the
terms is guessed at or decided between the issuers and verifiers.

9. JSON
Persistent DID
Name:Value Pairs
Name:Kaliya
Job:Ecosystems Director
Organization: CCI
}JWT
Signed by Issuer private key
Associated with Public key in DIDDoc

10. JSON-LD (JavaScript Object Notation) Linked-Data
JSON-LD supports an additional layer of context to map the
name part of the name-value pair to an RDF ontology.
What is an RDF ontology?
At the top in the @context field it references the
place where one can look up more about what
the terms below mean so in the schema.org
context there is a type called “Movie” and they
can then look up what are all the different terms
for this type.
JSON-LD supports disambiguation between
properties found in different credentials issued
by different issuers and so verifiers understand
what they are looking at.

11. In addition to all the features JSON provides, JSON-LD introduces:
● a universal identifier mechanism for JSON objects via the use of IRIs,
● a way to disambiguate keys shared among different JSON documents by
mapping them to IRIs via a context,
● a mechanism in which a value in a JSON object may refer to a resource on a
different site on the Web giving the ability to annotate strings with their
language,
● a way to associate data types with values such as dates and times,
● and a facility to express one or more directed graphs, such as a social
network, in a single document.
JSON-LD canonicalizes the attribute-value pairs in a predictable way
based on the information model being processed.

12. JSON-LD
Persistent DID
@Context: URL to find definitions
@Type: Job
Name:Value Pairs
Name:Kaliya
Job:Ecosystems Director
Organization: CCI
}LD-Signature
Signed by Issuer private key
Associated with Public key in DIDDoc
Look up the meaning of the terms in the credentials at a URL in RDF

13. Neither of these formats easily supports selective disclosure and
ZKPs, but both claim they can.
If an issuer puts each attribute in its own VC, then this is possible.
It isn’t possible for a holder to separate out VC claims when they
are bundled together within one VC.
Both JSON-JWT credentials and JSON-LD LD-Signature credentials
require that the holder share the whole credential with verifiers -
there is no partial share/show. This makes it harder to support
selective disclosure.

14. The second main format JWT is a part
of the JOSE framework. It provides no
means to support semantic
disambiguation but has the benefit of
being simpler for assertion format
implementations. “JOSE is the rice and
beans of cryptography standards.
It’s got everything you need to survive
and is easy to make, but its
extensibility model guarantees you
will be eating rice (base64url) and
beans (JSON) forever. That might
make you “fat” because base64url
inflates JSON.

15. On the other hand, Linked Data Proofs, as seen in Verifiable Credentials and
Verifiable Presentations, are like a pharmaceutical drug - really hard to build, but
capable of solving all kinds of problems and formally described by an
informationtheoretic model (molecular formula ~= RDF). Linked Data Proofs are
capable of working with other bases, other structured data formats (base58,
CBOR), and the extensibility model is anything that you can model in RDF.
Context determines the relevance of either model. Most people don’t go to a
pharmaceutical lab to make lunch, but most people who make drugs in their
kitchen also eventually end up sick.” - Orie Steele

17. JSON & JSON-LD Verifiable Presentation
Persistent DID
@Context: URL to find definitions
@Type: Job
Name:Value Pairs
Name:Kaliya
Job:Ecosystems Director
Organization: CCI
}LD-Signature
Signed by Issuer private key
Associated with Public key in DIDDoc
Verifiable Presentation Signed by the Holder with a
Nonce from the Verifier so that it can’t be “replayed”

18. Where are the schemas for ZKP-CL?
The schemas are defined in a document and they are written to an Indy ledger where
they can’t be changed. To update a schema, a new version must be created and written
to the ledger for future use. This schema is fetched from the ledger by verifiers when
calculating the verification. The underlying cryptography allows for calculations on what
is signed sharing key aspects of some but not all of the information. One can use a birth
date in the credential to calculate that a person is over 18 or 21 or 65.
The credential is anchored to a link secret that is known only to the holder (stored in
the holder’s software), and when the holder is issued a credential, it packages up a
cryptographic commitment to the link secret within another long number that the
issuer uses for the credential ID.
Unlike non-ZKP methods, zero-knowledge methods generally do not share a
correlatable identifier (such as a persistent or public DID) and also do not reveal
actual signatures. Instead, they only reveal a cryptographic proof of a valid
signature.

19. ZKP-CL Verifiable Credential
LINK SECRET
SCHEMA DEFINITION
Name:Value Pairs
Name:Kaliya
Job:Ecosystems Director
Organization: CCI
Signed by Issuer private key
Associated with Public key in DIDDoc
Posted to an Indy Ledger
CL Signature
CL Signature
CL Signature

20. ZKP-CL Verifiable Presentation
LINK SECRET
SCHEMA DEFINITION
Name:Value Pairs
Name:Kaliya
Job:Ecosystems Director
Organization: CCI
Posted to an Indy Ledger
CL Signature
CL Signature
CL Signature
}
VP involves
presenting proofs of
the CL Signatures.
The Verifier uses the
Schema from the
ledger + the public
keys found in the DID
of the Issuer to do the
calculations needed
for verification
calculations.

21. JSON-LD ZKP with BBS+ Signatures
It is based on the usage of BBS+ JSON-LD Signatures, which is a subclass of LD
Signatures, in combination with a JSON-LD credential schema.
By leveraging the technology of JSON-LD with a specific set of cryptographic key types and
algorithms, this mechanism is able to produce a VC that can be used to generate proof
presentations and ZKPs that selectively disclose attributes of the credential.
Multi-message digital signature schemes (like BBS+ and CL-Signatures) are able to sign an array
of messages, rather than simply a single message.
now they have the flexibility to break a message up into its fundamental attributes.
ability to derive and verify a proof of the digital signature over a subset of credential attributes.
The benefit of using this approach is first and foremost that it is interoperable with
existing schema technologies and credentials using JSON-LD, and by extension, is fully
compliant with the VC specification as it exists today.

22. JSON-LD ZKP with BBS+ Signatures Verifiable Credential
LINK SECRET or BLS Sig
@Context: URL to find definitions
@Type: Job
Name:Value Pairs
Name:Kaliya
Job:Ecosystems Director
Organization: CCI
Signed by Issuer private key
Associated with Public key in DIDDoc
BBS+ Signature
BBS+ Signature
BBS+ Signature
Look up meaning of the terms in the credentials at a URL in RDF

23. JSON-LD ZKP with BBS+ Signatures Verifiable Presentation
LINK SECRET or BLS Sig
SCHEMA DEFINITION
Name:Value Pairs
Name:Kaliya
Job:Ecosystems Director
Organization: CCI
BBS+ Signature
BBS+ Signature
BBS+ Signature
}
VP involves
presenting proofs of
the BBS+ Signatures
The Verifier JSON-LD
schema + the public
keys found in the
DIDDoc of the Issuer
to do the calculations
needed for
verification
calculations.
Look up meaning of the terms in the credentials at a URL in RDF

24. Lucy Yang
Community Director
John Walker
Community Architect
Kaliya Young
Ecosystems Director

25. The COVID-19 Credentials Initiative (CCI) is an open global community
whose purpose is to help deploy and help deploy privacy-preserving
verifiable credential projects in order to mitigate the spread of COVID-19
and strengthen our societies and economies.
● Formed in April 2020
● 400 participants who are active in standardizing and productizing VCs
● representing over 100 companies from all over the world.

26. CCI joined Linux Foundation Public Health (LFPH) in December 2020.
LFPH builds, secures, and sustains open source software to help public
health authorities (PHAs) combat COVID-19 and future epidemics. LFPH
has developed a relationship with a range of public health authorities as a
trusted partner in discerning emerging technology.

27. CCI/LPFH’s Goals and Activities
Open-Source Development
Understand existing landscape, define minimal viable
components for open-source development, and
develop/repurpose codebases.
Open Standards
Understand existing landscape, align interoperability efforts,
and facilitate the development of a common, open standards
for vaccine and test credentials.
Communications
● Public Health Authorities: Helping them understand the underlying tech, where the standards are going, and what's the
minimum-viable way to get something implemented that doesn't create interoperability headaches later.
Commercial Entities: Working with LFPH members and CCI participants towards a list of potential vendors as a start
● General Public: Mainstream media (e.g. NBC, CNN Business, CNBC etc.)
Use Case Implementation
Workstream
Rules & Governance
Workstream
Vaccine Credentials Focus
Group

28. CCI/LPFH’s Goals and Activities
Use Case Implementation
Workstream
This workstream identifies
verifiable credentials (VCs) that
are most useful to the COVID-19
response and provides a forum
and platform for those who are
implementing COVID-19 VCs to
present their projects/solutions
and get community input.
Rules & Governance
Workstream
This workstream defines rules
and guidelines for general or
particular COVID-19 verifiable
credential use cases and
develops MVP governance
frameworks to enable solutions
to be deployed at speed.
(Working under ToIP)
Vaccine Credentials Focus
Group
The goal is to start with forming
geography-focused subgroups
under this group to bring together
key stakeholders, especially
public health authorities, to
identify trusted and scalable
ways of rolling out vaccine
credentials.
(Formed)
United States
Focused
Additional
Geographies
(forthcoming)
CCI Governance Framework V2.0
14
Use-Cases
Explored
Demo’s from 20+ VC
Implementations/POC

29. CCI/LPFH’s Goals and Activities: Open Standards
A Unified Verifiable Credentials
Data Format
Standardized VC Exchange
Protocols
WHO assembled a panel of
experts to work on Smart
Vaccination Certificate.
Kaliya Young, our
Ecosystems Director, is on
two of the three
workstreams.
Verifiable Credentials Flavors Explained

30. CCI/LPFH’s Goals and Activities: Open-Source Development
Verifiable Data Registry
Universal Wallet?
Basic Verifier App?
Basic Issuer App?
Minimal Viable User Experience for individuals and businesses
to start fast, secure and at little to no cost.
Minimal Viable Components for PHAs and business to work
with their solution providers to contextualize easily,
cost-effectively without interoperability headaches.

31. Community Venues
CCI Main E-mail Group - To receive regular CCI-wide announcements and news
CCI Sub-Groups - To receive regular activity notifications and start/join group discussions
● Use Case Implementation Workstream
● Rules & Governance Workstream
● Vaccine Credentials Focus Group
● Future groups...
Bi-weekly Community Newsletter - To receive high-level CCI updates and related news
(Automatic subscription if you join the above groups)
Social Media presence : Twitter, Linkedin, Medium
LFPH Slack Ongoing activity: Relevant channels #cci #vaccines #cci-vaccinecredentialsfg-us

36. Extra Slides Below

37. Implementation Challenges
Emerging Standards &
Technology
Communications to the
Public & Public Trust
Existing Infrastructure and
Workflows
Ecosystem Building and
Governance

38. Communications to the
Public & Public Trust
Existing Infrastructure and
Workflows
Ecosystem Building and
Governance
Implementation Challenges
Emerging Standards &
Technology
W3C Verifiable
Credentials Data Model
VC-Related Technical
Specifications
Vaccine Credential
Related Standards

39. Communications to the
Public & Public Trust
Ecosystem Building and
Governance
Implementation Challenges
Existing Infrastructure and
Workflows
Issuer/Sourcing
Information Flow
Vaccine Record
Registries
Compatibility with
Healthcare Systems
Emerging Standards &
Technology

40. Existing Infrastructure and
Workflows
Emerging Standards &
Technology
Ecosystem Building and
Governance
Implementation Challenges
Communications to the
Public & Public Trust
The WHAT The WHY The HOW

41. Existing Infrastructure and
Workflows
Emerging Standards &
Technology
Implementation & Challenges
Communications to the
Public & Public Trust
Ecosystem Building and
Governance
Governance Authority
Trust
Publishes
Governance
Frameworks
● Who define which issuers have the authority to
issue vaccine credentials?
● How is Sarah supposed to know if the verifier
has the authority to check her credential?
● What if Sarah doesn’t have a smartphone?

42. Thank you! Questions?

43. Vaccine confirmation in a
Verifiable Credential
Verifiable
Presentation
Primary Areas of Group Focus - US Jurisdiction example
Credential Acquisition Claim Presentation
Interoperability

44. Existing (as example) US Covid-19 Information Systems Data
Flow

45. Why Verifiable Credentials: VCs vs. Paper Credentials
Verifiable Credentials (VCs) have the potential to provide the closest
experience to paper credentials while offering additional benefits.
“I need to see your photo ID as
well”
“This is your only legitimate
proof of vaccination, so
please keep it safe.”
Sarah

46. • What if Sarah lost her only card?
• What if Sarah fabricated her card? How was the verifier supposed to know?
• What if Sarah accidentally dropped the card in the water and the text went blurry?
• Did Sarah want the verifier to see all her information on the driver’s license and
vaccination record card?
Verifiable Credentials (VCs) have the potential to provide the closest
experience to paper credentials while offering additional benefits.
Why Verifiable Credentials: VCs vs. Paper Credentials

47. Vaccine Credential
in VC
Verifiable
Presentation
Verifiable Credentials (VCs) have the potential to provide the closest
experience to paper credentials while offering additional benefits.
Why Verifiable Credentials: VCs vs. Paper Credentials

48. • The vaccine credential comes from a place which has the authority to issue it.
• The vaccination actually happened
• The vaccination happened to the person who presents this piece of credential
• The credential hasn’t expired if there is an expiry date
Verifiable Credentials (VCs) have the potential to provide the closest
experience to paper credentials while offering additional benefits.
Why Verifiable Credentials: VCs vs. Paper Credentials

49. No direct integration or third-party intermediary
Vaccine Credential
in VC
Verifiable
Presentation
Trust
Verifiable Credentials (VCs) have the potential to provide the closest
experience to paper credentials while offering additional benefits.
Why Verifiable Credentials: VCs vs. Paper Credentials

50. Vaccine Credential
in VC
Verifiable
Presentation
Public Utility
Why Verifiable Credentials: VCs vs. Paper Credentials
Verifiable Credentials (VCs) have the potential to provide the closest
experience to paper credentials while offering additional benefits.

51. User Control
Interoperability Privacy-Preserving
Tamper-Evident Durability
Portability
Why Verifiable Credentials: VCs vs. Paper Credentials
Verifiable Credentials (VCs) have the potential to provide the closest
experience to paper credentials while offering additional benefits.
Binding
No Single Point of
Failure

52. PDF Document Proprietary Software Network/Platform
PDF is easier to store and has
more durability, but the key
drawback is it is not
tamper-evident and not
privacy-preserving.
Proprietary software that is not
built on open standards will
create silos and monopolies. And
it won’t meet the interoperability
vaccine credential needs.
Network/Platforms that are not
built on open standards will
create similar silos and won’t
meet the interoperability need
either.
Why Verifiable Credentials: VCs vs. Other Digital Alternatives

53. CCI Vaccine Credentials Focus Group Positioning
Open-Source Development
Document existing landscape, define minimal viable
components for open-source development, and
develop/repurpose codebases.
Open Standards
Understand existing landscape, align interoperability efforts,
and facilitate the development of a common, open standard
for vaccine credentials.
CCI Community
●
Use Case Implementation
Workstream
Rules & Governance
Workstream
Vaccine Credentials Focus
Group