This abstract was submitted to and presented at CCRC International Conference 2022.

Dependency among Data, Code, Governance, andOperation in Trust
Shigeya Suzuki*1, Tatsuya Kurosaka*1, Jun Murai*2*1 Graduate School of Media and Governance, Keio University*2 Keio University

In this extended abstract, we discuss the chain of the trust model in terms of Data, Code,Governance, and Operation to reveal the issues around the scheme to establish the chain oftrusts in a holistic view.
Online Services, Digital Identity, and Privacy
People capable of working with information technology typically have multiple Internetservice accounts. In the beginning, Internet service providers just allowed users to create theiridentities within their system. This identity information typically includes login identifier andpassword. But nowadays, the service providers often require users to bind their real identities
with the account for the system. These "Digital Identities" consist of the Person Identifiable
Information such as name, day of birth, postal addresses, mobile phone numbers, etc.
Technically, these pieces of information are called "Attributes of Identity [REF-Attribute]."Some services require our Digital Identity for our sake. Banking services require ourdetailed information because they maintain our essential assets, identify us for later necessarycommunication, and for regulations. In other words, the reason why they need our identity is
to correctly bind our information with the assets they're maintaining for us. Banking services
don't need to use the customer's identity outside their services.
On the contrary, some businesses want our Digital Identity for their own businessmerits. Social networking service providers often want detailed information to provide better
results. The results may or may not provide good values for the users. In other words, theyneed our identity because they want to profile us from our activities on the Internet as muchas possible. Thus, to achieve their purpose, they want to track and consolidate our activities
on the Internet.
Internet services are evolving quickly, and sometimes, we need to reveal our Digital
Identities in specific contexts — at least partially. Since we live in a digitalized world, once
we reveal part of the attribute, it is usually tough to revert the disclosure of the attribute later.
Due to this fact, it is always safer to provide a minimum amount of information. For example,
if we want to buy alcohol, we may need to prove that we can purchase alcohol or above. Wewill use identification cards with photos in the Physical World, such as driver's licenses.
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While you only need to prove that you are at a certain age, we reveal the actual age
unnecessarily. From this point of view, current physical identification card-based proof is notideal. Suppose we need to reveal a digital identification card to somebody since the person
who checks the age can easily copy the entire information. In that case, it might be more
severe than the Physical World case. Thus, there is an intense desire for attribute-based proof
with minimum disclosure of the person's attributes.
Trust and Authentication work
Trust is a complex concept. Let us introduce a definition of "Trust" in this paper: When wetrust a subject, we do not need to rely on other entities to judge the trustworthiness —assumption that the subject acts as expected. But, before taking action based on trust, youneed to be sure the entity you're acting on really is the subject you believe to be with; Before
the action, you need to judge the entity's authenticity. You may need to rely on other entities
with trust to verify authenticity.
The following section discusses the authentication model and the relationship to Trustin each Physical World and the Cyber World.
Authenticating Subjects in Physical World
Trust in the physical world is a blurred concept. Most of us request banks to keep our assets
safely. One of the possible reasons we opt to do this is that keeping money at a banking
service is secure than keeping money in our residence. Why do we trust these banks? Maybe,
it is a major bank, has a long business history, owns multiple bank locations, or possibly yourparents using the service.
Besides trusting a subject, you also need to be sure about the subject’s authenticity.
Some documents help you judge the subject's authenticity in Physical World. You can use
certificates (including identification cards), physical confirmation of existence, or otherattribute-like information as a basis for making judgments on the authenticity of the subject.
Unfortunately, the authenticities of these certificates are weak. The certificates may
have physically unique characteristics, but it is hard to judge whether the certificate is valid
without the help of devices or other schemes that can judge the certificates' authenticity. Suchdevices or schemes are not common; thus, people need to decide only with a visual inspection
which might be not good enough or inefficient.
Authenticating subjects in Cyber World
Trust in the Cyber World is modeled based on the Physical World; due to that, the model has
both strengths and weaknesses. When creating a user service on the Internet, the systemarchitect must choose an authentication mechanism that resolves the user-provided
information into the user's Digital Identity. Depending on the authentication mechanism, themechanism itself requires the trust of the entities involved. For example, suppose the system
requires a user-specified delivery-verifiable email address which the user owns. In that case,the system relies on the email delivery mechanism, which depends on multiple components,
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including mail servers, domain name system, etc. The fundamental component ofauthenticating a subject in the Cyber World depends on Public Key Cryptography. With
Public Key Cryptography, the owner of a particular key can prove the ownership of theprivate key by providing the signature of some information to the verifier by using its private
key. Assuming each entity in the system owns Public Key Cryptography key pairs, the entity
holds complete control of the private key. One entity — issuer — can describe another entity— subject — as relationship data with a signature using the issuer's key. The relationshipdata consists of information of the subject, including the subject's public key, related
metadata, information of the issuer, which includes the public key of the issuer, signed withthe issuer's private key. The relationship data is often called the "Public Key certificate of thesubject." X.509 Public Key Infrastructure (PKI)[PKI] is the standard widely deployed on theInternet.
Single Public Key Certificate only describes a single issuer-to-subject relationship.
When connecting a client to a server using PKI certificates, it is possible to verify the publickey in use if the verifying entity owns the peer's PKI certificate before connecting. But themost cases, the client does not know the server's certificate before the connection. Also, sincea self-issued certificate is not trustworthy, a certificate issued by a trusted third party isnecessary. Thus, PKI provides the model to create a hierarchy of relationships of certificates.
Entities named "Certificate Authorities" (CAs) issue a certificate for a subject. Byhierarchically organizing CAs, when verifying the peer's public key, the verifier only needs toknow "root" CA, then traversing tree hierarchy towards the peer's certificate to verify. This
traversed path creates a chain of certificates starting from the "root" CA towards the peer's(leaf) certificate. We call this "chain of trust." The chain of trust provides the way to prove apublic key in the certificate is owned by the subject described in the certificate. Thecertificate only verifies the integrity of the public key certificate. That means only thesubject's relationship with the public key and nothing beyond that. The PKI does not provide
the "Trust" similar to the "Trust in the Physical World" described in the prior section. It
merely provides the information that the peer is the peer the program wants to connect.
The Root of Trust and its variation
The PKI system provides a distributed trust architecture. Each piece of the "chain" of trust
can be separately issued and verified. The chains of trust are helpful if and only if theparticipating parties share the list of roots. Thus, how these root CAs operates is extremelyimportant. The operation of the CAs, especially CAs in closer to the root, needs special care.
Also, it is essential to understand how the software system trusts and refers to the Root CAs.
Each of the major operating systems and some Web Browsers maintains Trust Stores for thesoftware. Each software vendor maintains each of the Trust Store according to its policies.
Their policies, including Certificate Authority Policy, are documented [MS][APPLE][CAB]
publicly.
Other than relying on Trust Stores, a number of the Root of Trust discovery
mechanisms have been proposed and deployed recently. One way is to specify Root of Trustby a well-known URL scheme to retrieve JWKS[JWKS]. The Smart Health CardPage 3 of 5

specification [SHC] uses this scheme. The Smart Health Card is one of the formats selected
for the Digital Agency of Japanese Government [JVC] vaccine certificate. The issuer of thescheme is an URL. There is a standardized step to translate the URL into a JSON file with thehelp of DNS, HTTP, and TLS protocols.
Governance of the Elements of TrustThe establishment of the Chain of Trust is related to managing two data objects. The firstdata objects are the Public Key or the Public Key relationship data (a piece or a part of achain). The second data objects are the data related to the discovery mechanism of the firstobject.
For a typical X.509 based PKI deployment, CAs handle the first data objects. All dataobjects are ready when the verification process starts without relying on anything. On
building the chain of trust, usually, the software retrieves the subject's certificates alongside
the certificates of intermediate CAs. Then, find the root of trust matches with the justretrieved chain of trust in the Trust Store.
For the Smart Health Card (SHC) style JWKS chain of trust deployment, multiple
configurations among various parties are necessary: configuration of a domain name, a serverthat holds the JWKS, and the generation of the public key X.509 chain of trust is necessary.
For the retrieval, the verifier synthesizes the URL for the JWKS JSON from the issuer URLvalue. Then verifier retrieves the file using HTTP with the help of DNS, possibly with TLS.
After parsing the JWKS JSON object, the verifier finds either public keys or a set of X.509
certificates. Some small but influential data is involved in resolving the process of the chainof trust. The entity that controls the data manages the data according to a predeterminedpolicy, and governance is in place.
What is important here is whether the subject certificate owner influences these
influential data. For the X.509 case, each Trust Store for the software is such data controlled
by the software owner; the subject certificate owner, alongside with intermediate CA owner,needs to follow the Trust Store's policy. For the SHC case, the subject certificate owner canfully control the certificate's existence and resolve as expected, as far as dependency on DNS
and the server's ownership stays intact.
Conclusion
Verification of the authenticity of Digital Identity is an essential mechanism for providing
services in Cyber World. As we discussed, Public Key Cryptography is the key toestablishing the chain of trusts. While X.509 PKI-based mechanism with Trust Store in theoperating system is the most prevalent way to establish the chain of the trust, the ownershipand control of the Trust Store are sometimes unfavorable.
The mechanisms introduced in Smart Health Cards and related standards such as
Verifiable Credentials [VC] and Decentralized Identifier allow establishing the chain oftrusts. Since these new alternative schemes possibly provide less restriction of establishing achain of trust, we may apply the scheme with a detailed study on the different, possiblycomplex governance model.

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References[REF-Attribute] International Organization for Standardization. (2019). IT Security andPrivacy — A framework for identity management — Part 1: Terminology and concepts (ISOStandard No. 24760-1:2019). https://www.iso.org/standard/77582.html[PKI] Internet Engineering Task Force. (2008). Internet X.509 Public Key Infrastructure
Certificate and Certificate Revocation List (CRL) Profile (Internet RFC No. 5280).
https://www.rfc-editor.org/rfc/rfc5280[MS] Program Requirements - Microsoft Trusted Root Program.
https://docs.microsoft.com/en-us/security/trusted-root/program-requirements[APPLE] Apple PKI. https://www.apple.com/certificateauthority/[CAB] CA/Browser Forum. https://cabforum.org/[JWKS] Internet Engineering Task Force. (2008). JSON Web Key (JWKS) (Internet RFC7517). https://datatracker.ietf.org/doc/html/rfc7517[SHC] Smart Health Cards. https://smarthealth.cards[JVC] Ministry of Health, Labor and Welfare, Japan. (2021). New Coronavirus Infection
Vaccination Certificate (Vaccination Certificate).
https://www.mhlw.go.jp/stf/seisakunitsuite/bunya/vaccine_certificate.html[VC] World Wide Web Consortium. (2021). Verifiable Credentials Data Model 1.1. W3C
Recommendation. https://www.w3.org/TR/vc-data-model/[DID] World Wide Web Consortium. (2021). Decentralized Identifier (DIDs) v1.0, Proposed
Recommendation. https://www.w3.org/TR/2021/PR-did-core-20210803/

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