2. Focused Research (1)Blockchain-based
Identity Management and Distribution
2.1 Introductions

Real-world entities are linked with digital-world entities, andEveryday, it seems, media reports about various services

a unique identifier (which we will denote “ID”) is assigned

based on blockchain technology appear. Among these are

to identify the digital-world entity. The notion of an ID as

many unfortunate ideas that merely use blockchains as a dis-an identifier must be kept conceptually separate from thetributed database, so much so that a number of flowcharts

various identity information that is bound to that ID. Further,for determining whether you really do need to use block-because realms (the scope within which the ID is valid andchains have been published*1. There are several methods

can be used to identify something) are separately defined forof classifying blockchains; broadly, they can be classified

each ID space, a single, unique entity in the real world caninto private-use blockchains and public blockchains thathave multiple IDs even within the same realm.

underpin the security of cryptographic assets. With publicblockchains, it is necessary to incentivize ongoing mining to

Now the reason IDs are assigned in the digital space is that

extend the chain; for cryptoassets such as Bitcoin, it is nec-

there is a need for third parties on the network to identify

essary to extend the chain based on predefined rules. With

the entities to which IDs are assigned. The act of authenti-

cryptoassets, the main reason for using blockchain is tocation accompanies all sorts of activities in the digital world.

transfer assets from one address to another, but efforts are

Authentication allows access to various resources and ser-also being made to use this blockchain-based value-transfer

vices, for instance.

platform for other applications. These are being called second layer or Layer 2 applications.

This act of authentication can be accomplished by using
pairs of tokens (secret information) and credentials (public

Here, we look at developments in ERCs (Ethereum Requests

information). According to the definition in NIST SP 800-

for Comment)*2 used for credentials (identity information) from63, a token contains a secret known to the user to which*3

among the second-layer services for the Ethereum blockchain .

the ID in question has been assigned, and credentials bind

We will also touch on use cases in which such credentials arevarious attributes to the ID. Cryptographic techniques are

stored in the blockchain, enabling public certifications, suchused to ensure the integrity of credentials. Credentials use

as student or employee IDs, to be verified digitally. Finally,

cryptographic techniques to ensure content integrity. When

we also go over why several vendors and consortiums havethe entity that holds the ID seeks verification of his or her

put forward concepts such as Decentralized Identifiers (DIDs)

attributes by a third party in the digital world, the token (se-and Self-Sovereign Identity (SSI), where the user is in control

cret information) can be used to verify that the holder of theof managing their own identity, and take a look at the focus

ID is the entity to which it was assigned.

on technology for managing credentials based on blockchains.
When a credential is presented together with an authentica-

2.2 IDs and Credentials as Identifiers

tion operation, a receiving third party can verify what sort ofIn focused research pieces back in 2015, we reported on

entity the ID is using the attributes given in the credential. In

trends in ID management technology at the time*4*5*6. Here,addition to authentication in this manner, credentials are also

we consider IDs in the narrow sense of identifiers.

used for authorization in some cases. An X.509 certificate is*1

NISTIR 8202, “Blockchain Technology Overview” (https://doi.org/10.6028/NIST.IR.8202), Figure 6: DHS Science & Technology Directorate Flowchart.

*2

Ethereum Improvement Proposals (http://eips.ethereum.org/).

*3

Ethereum Project, Developer Resources (https://www.ethereum.org/developers/). In this volume, we do not cover technology related to smart contracts, a key
feature of Ethereum.

*4*5Internet Infrastructure Review Vol. 26, “1.4.3 ID Management Technology” (https://www.iij.ad.jp/en/dev/iir/pdf/iir_vol26_EN.pdf).
Internet Infrastructure Review Vol. 27, “1.4.2 ID Management Technology: From a Convenience and Security Perspective” (https://www.iij.ad.jp/en/dev/iir/pdf/
iir_vol27_EN.pdf).

*6

Internet Infrastructure Review Vol. 28, “1.4.3 ID Management Technology: Online Authentication Methods Not Using Passwords” (https://www.iij.ad.jp/en/dev/iir/
pdf/iir_vol28_EN.pdf).

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2. Focused Research (1)an example of a credential because it binds a public key with

Smart contracts, a method for automatically executing

one or more IDs. And in fact, SSL/TLS client authentication

contracts and performing services, are a new concept put

is one case of this. Deploying a personal X.509 certificate

forward by Nick Szabo in 1997 and thus predate Bitcoin. A

on the browser side allows a user to log in to a server, andcommonly cited example of a smart contract is the vending

this is used in applications like corporate online banking.

machine. When certain conditions are met by two processes,

A specification for X.509 Attribute Certificatesprovidesnamely that the user inserts payment for the desired bever-a method that is closer to credential-like usage. Attributeage into the machine and the user subsequently presses thecertificates differ from ordinary X.509 certificates in that

button corresponding to that beverage, a sale is automaticallythey do not contain a public key. A serial number used toinitiated. As well as being used for cryptoassets, Ethereum

identify the certificate is placed in an area for storing identi-

is also being viewed as a distributed application platform

fiers called the Holder so as to specify the X.509 certificate,enabling the creation and execution of smart contracts*11.

and attributes bound to the certificate holder (subject) are

ERC-725 defines a Solidity interface for the behavior of athen stored. Here the realm can be understood to be theproxy account. Solidity is a language used to write distributed

certificates issued by the certification authority, the ID toapplications. ERC-725 refers to ERC-735*12 and ERC-780*13

be the serial number, and the credentials to be the attributeand provides a framework for distributing credentials on thecertificate. Credentials can be written to X.509 Attribute

Ethereum blockchain based on these specifications. In theCertificates, but they are not actually implemented in appli-

ERC-725 document, credentials are called claims. ERC-735

cations that general users are likely to encounter, such as

describes the format of claims, and ERC-780 describes anbrowsers, so there are hardly any cases of them being used

Ethereum Claims Registry (ECR). Under the framework spec-

at present.

ified in the Ethereum blockchain realm, an ID (identifier) is
​​ an

*7

Ethereum address (note that it is not a contract address), and2.3 Overview of ERC-725

the identity information of the identity holder bound to the

ERC-725*8 was proposed in October 2017 by software

address is certified by credentials, called claims. The claim

engineer Fabian Vogelsteller*9, known for developing theissuer can issue a claim to any entity on the Ethereum block-ERC-20 token standard and web3.js. Like the IETF’s RFCs,

chain using a private key in the claim issuer’s possession. The

ERCs (Ethereum Requests for Comment) are documented

identity holder passes the claim to be verified to the claim

proposals for improvements that anyone can author; thechecker via some method, and the claim checker can verify

format and writing guidelines are given in ERC-1. A major

the claim’s veracity by verifying the digital signature. It isfeature worth noting is that authors are asked to keep theirenvisioned that this series of verification tasks can be per-proposals compact. A similar class of documents exists informed both online and offline*14.

the Bitcoin community, known as BIPs (Bitcoin Improvement
Proposals)*10. The method for reducing transaction data

Claims as specified in ERC-735 have the following simple

known as SegWit, for instance, is defined in BIP-141.

data structure.

*7

RFC 5755, “An Internet Attribute Certificate Profile for Authorization” (https://datatracker.ietf.org/doc/rfc5755/).

*8

ERC-725 version 2: Proxy Account (https://github.com/ethereum/EIPs/issues/725) (http://eips.ethereum.org/EIPS/eip-725).

*9

Fabian Vogelsteller (http://frozeman.de/blog/).

*10

BIP (Bitcoin Improvement Proposals) (https://github.com/bitcoin/bips).

*11

Ethereum Project white paper (https://github.com/ethereum/wiki/wiki/White-Paper).

*12

ERC-735: Claim Holder (https://github.com/ethereum/EIPs/issues/735).

*13

ERC-780: Ethereum Claims Registry (https://github.com/ethereum/EIPs/issues/780).

*14

Fabian Vogelsteller, ERC Identity (https://www.slideshare.net/FabianVogelsteller/erc-725-identity).

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So under the ERC-725 framework, anyone can issue a claim.

struct Claim {uint256 topic;
uint256 scheme;
address issuer;
bytes signature;bytes data;
string uri;}

In other words, anyone can be a claim issuer, so you canissue a claim to anyone as long as you know their Ethereum
address. A key issue, therefore, is how to establish trust fora claim issuer and how to value the claims issued by thatissuer. There also appears to be functionality to allow, for

ERC-735 claims should be implemented to enable the iden-

example, claims to be revoked and the Ethereum address totity holder to present them to the claim checker, and a key

be swapped out, but the specification is still incomplete incharacteristic is that the data are portable. ERC-735 provides

this regard. It also seems that discussion over what reputa-

a zone for writing URIs to an area that is not ToBeSigned,tion system to use for issuers has only just begun.

and it is here that data pointing to the identity informationis shared via a distributed file system such as IPFS*15. The

So we are straddled with a problem of reputation, and we

ERC-725 Alliance*16 has an open-source project related towill probably need to work through a few stages before we

ERC-725. Also, a number of samples are available on

are ultimately able to distribute claims the way we would

sites*18 built using this demo implementation, showing how

like. My view is that the notion of claims will gradually gain

the veracity of claims can be verified in the browser. It is

traction via the following three steps. In the first stage, ac-worth noting that the specification allows you to sign yourquaintances in closed networks, such as SNS, will casuallyown identity information and thus make your own claims

issue claims to one another. This phase will determine scal-

about yourself.

ability. The next stage will see the formation of a framework*17

Table 1: Elements of the ERC-735 Claim Structure

14

Topic

Currently marked as ToBeDefined. A 256-bit space expected
to contain information on the topic (or type) of claim.

SchemeToBeDefined. A 256-bit space to hold the processing
method or signature algorithm to use, which would refer toseparately defined schemes.

IssuerA contract address or the Ethereum address of the key
used to sign the signature.

Signature

Note that the signed data needs to be of the following
structure: {identity holder’s Ethereum address, topic, data}

Data

The hash of the identity information (claim data). The identity
information itself is not written here, so sensitive information
is not being written to the blockchain.

Uri

A URI pointing to the identity information. HTTP link, IPFS
URI, or such like.

*15

IPFS (InterPlanetary File System) (https://docs.ipfs.io/introduction/).

*16

ERC-725 Alliance (https://erc725alliance.org/).

*17

ERC-725 Alliance, “Repository for code and discussion around ERC725 and related standards” (https://github.com/ERC725Alliance/erc725/tree/master/contracts/contracts).

*18

ERC 725: Demo implementation by Origin Protocol (https://erc725.originprotocol.com/); Origin Protocol, Inc. (https://www.originprotocol.com/).

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2. Focused Research (1)for ranking issuers using existing user evaluation/reportingon the scene, so when selecting a platform, the businesssystems to assess whether they have issued incorrect

continuity prospects need to be taken into account.

claims or not. And finally, this will develop into a completely
distributed, automated reputation system (Figure 1).

As discussed so far here, claims embody a simple mechanism, but if the Issuer is trustworthy and the second-layer

The Blockcerts

project is another example of the use of

specification works properly, it is understood they can be

portable claims in a vein similar to ERC-725; there are open-

used on a semipermanent basis so long as the reliability ofsource code

*19

available as well.

the Ethereum blockchain remains intact. So the digital issu-

Blockcerts is based on prototypes developed at the MITance of diplomas is one application apt for making good use

Media Lab and Learning Machine. Work is ongoing to extendof blockchain technology, and indeed, some such services

Blockcerts to implement multiple blockchain types, including

have appeared in Japan. Once trusted organizations do not

Bitcoin and Ethereum. A smartphone app called Blockcerts

persist indefinitely, as attested by the closure of private

Wallet has also been implemented and released, and MIT

schools in regional areas and the discontinuation of certi-

is now using the Blockcerts technology to write students’fying exams by local governments. There are even cases

diplomas to the blockchain*22. And a Spanish university hasof physical certificates issued by such organizations no lon-

also announced that when issuing degree certificates, it will

ger being validatable. Hopefully, we are bound for an era

use the SmartDegrees platform so that they can be man-in which claims distributed via an open framework, as dis-

aged on the Ethereum blockchain*23. The situation is a tadcussed here, provide an alternative to physical certificates.

*20

and verification demos*21

chaotic at present with multiple such second-layer platforms

A framework whereby Reputators evaluate
the Claim Issuer is needed

Trust
Claim Issuer

Can the Claim’s veracity be determined?
Certified

Claim

Claim

Claim

Claim

Claim

Claim

Claim

Identity Holder

Claim Checker

Figure 1: Framework for Issuing and Valuing Claims*19

Blockcerts (https://www.blockcerts.org/).

*20

Repositories of the Blockcerts project (https://github.com/blockchain-certificates).

*21

Example Blockcerts (https://www.learningmachine.com/new-product/examples/).

*22

MIT News, Digital Diploma debuts at MIT (http://news.mit.edu/2017/mit-debuts-secure-digital-diploma-using-bitcoin-blockchain-technology-1017).

*23

Universidad Carlos III de Madrid is issuing degree certificates with blockchain (https://www.uc3m.es/ss/Satellite/UC3MInstitucional/en/Detalle/Comunicacion_C/1371252827656/1371215537949/Universidad_Carlos_III_de_Madrid_is_issuing_degree_certificates_with_blockchain).

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2.4 Decentralized Identifiers, DIDs

The notion of Decentralized Identifiers (DIDs) emerges from

As identifiers, IDs are assigned within a specific realm. When

this backdrop. A feature of DIDs is that they are not valid

it comes to authenticating across realm boundaries, the no-

IDs only in one specific realm and there is no centralized

tion of the ID Federation comes into play and often appears

presence that manages the IDs. This is seen as highly com-in a single sign-on context. Credentials such as the X.509

patible with the notion of Self-Sovereign Identity (SSI)*24

Attribute Certificates and ERC-735 claims we have discussed

proposed by the nonprofit Sovrin Foundation*25. SSI is simi-

only circulate within the realm in which they were issued.

lar to the idea that individuals have the right to control their

In reality, identity providers, whose role is also to issue IDs,

own information. The term is used in recognition of the need

do not exist in isolation. To enable the login functionality offor individuals to own and manage their own identities with-service providers, such as SNSs, to be used from external

out going through a central managing authority. Credentials

services, that functionality is split off into the identity pro-such as ERC-735 claims, as discussed above, can be passed

vider role. As such, in cases where ID linking functionality isaround without the identity holder intending it. Not so withused to log in to separate services, there is a risk that the ID

SSI; instead, the idea is that the identity holder has sover-will suddenly stop working because it is operated by a partic-

eignty over the distribution of his or her credentials.

ular company or organization. Thus, the deactivation of one
ID could result in an inability to use several other services.

The nonprofit ID2020 Alliance*26 is an organization that

The deactivation—or in the worst case, deletion—of an ID

seeks to achieve privacy protection and portable, user-cen-because an SNS operator decided that inappropriate content

tric identity management. There is also a project*27 that

had been posted can have negative impacts, and indeed there

looks to use claims written to a blockchain as an alterna-

have been various real-world cases of this.

tive to passports, analogous to the way people seek to use*24

The Sovrin Alliance, “Sovrin: A Protocol and Token for Self-Sovereign Identity and Decentralized Trust” (white paper, version 1.0, January 2018) (https://sovrin.
org/wp-content/uploads/Sovrin-Protocol-and-Token-White-Paper.pdf).

16

*25

The Sovrin Alliance (https://sovrin.org/library/rise-of-self-sovereign-identity/).

*26

ID2020 Alliance, The Alliance Manifesto (https://id2020.org/manifesto).

*27

Taqanu (https://www.taqanu.com/impact).

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2. Focused Research (1)cryptoassets rather than legal currency in cases where the

distributed ledger technology or other form of decentralized

reliability of nationally issued currencies has diminished.

network*32. ERC-735 claims use Ethereum addresses as the

The idea can be interpreted as follows: data correspond-

ID space, but a method has also been proposed for wrappinging to claims that everyone recognizes and that are issued

Ethereum addresses in the W3C DID format instead of using

by credible institutions can provide a passport-like means

them as raw DIDs*33. So W3C DID is being promoted as aof personal identification. The Sustainable Development

global ID capable of representing a range of IDs. The exis-

Goals (SDGs)*28 compiled by the United Nations in 2015

tence of DIDs alone only solves the issue of nonconflicting

state Target 16.9 as: “By 2030, provide legal identity for

numbering, but in conjunction with the claim use cases*34

all, including birth registration”. And the ID2020 Technicaland the verifiable credentials (originally called claims, theRequirements*29 have been formulated in an attempt towording was later changed to credentials) data format*35,

assist the world’s “identity refugees”, thought to number

they are poised to solve the various other issues faced.

over a billion. The document covers seven categories—
applicability, identification, authentication, privacy, trust,Group work at the Web of Trust VIII event in March 2019

interoperability, and recovery—and is highly useful as a de-(RWOT8)*36 and the 28th Internet Identity Workshop*37

sign guideline of this type.

in April 2019 dealt with many topics centering on DIDs
and SSI. The 2019 annual meeting of the IGF (Internet

The intention behind DIDs, meanwhile, can be gleaned from

Governance Forum)*38 will also cover DID-related technol-

documents developed by the W3C*30*31. The W3C defines

ogy and encompass discussion of governance. So looking

a DID as a globally unique identifier that does not require aahead, many people are lining up to drive the discussion

centralized registration authority because it is registered withforward.

*28

Transforming our world: the 2030 Agenda for Sustainable Development (https://sustainabledevelopment.un.org/post2015/transformingourworld) (https://www.
un.org/ga/search/view_doc.asp?symbol=A/RES/70/1&Lang=E).

*29

ID2020 Technical Requirements: V1.0 (https://docs.google.com/document/d/1L0RhDq98xj4ieh5CuN-P3XerK6umKRTPWMS8Ckz6_J8/edit).

*30

W3C Credentials Community Group (https://www.w3.org/community/credentials/).

*31

W3C Verifiable Claims Working Group (https://www.w3.org/2017/vc/WG/) (https://github.com/w3c/verifiable-claims).

*32

Decentralized Identifiers (DIDs) (https://w3c-ccg.github.io/did-spec/#decentralized-identifiers-dids); latest version as of this writing: v0.13, dated Jun. 3, 2019*33

eth DID Resolver (https://github.com/uport-project/eth-did-resolver).

*34

Verifiable Claims Use Cases (https://www.w3.org/TR/verifiable-claims-use-cases/).

*35

Verifiable Credentials Data Model 1.0 (https://www.w3.org/TR/verifiable-claims-data-model/); latest version: Mar. 2019; a W3C Candidate Recommendation as ofthis writing.

*36

Rebooting the Web of Trust VIII: Barcelona (March 2019) (https://github.com/WebOfTrustInfo/rwot8-barcelona) (https://www.weboftrust. info/pastevents.html).

*37

IIW (The Internet Identity Workshop) Workshop Proceedings (https://internetidentityworkshop.com/past-workshops/).

*38

IGF 2019 Workshop Selection Results (https://www.intgovforum.org/multilingual/content/igf-2019-workshop-selection-results).

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2.5 Other Related Developments

It is theoretically possible for people to be scored unfairly

In May 2019, Microsoft unveiled a platform to handle

based on obscure logic because they live in a particular re-

DIDs based on the Bitcoin blockchain. Two blog posts

gion or on the basis of race, religion, etc. Hence, ethicalon May 15 describe its future activities in this area*39*40.

considerations must be taken into account. The same can

And it has published a white paper on DID*41. From thesebe said for the reputation mechanisms of real-world entities,

sources, it is apparent that the W3C DID is being used asa concern I also noted in relation to ERC-735 claims.

the ID space and that the Sidetree protocol developed by
the Decentralized Identity Foundation (DIF)*42 has been ad-

Thus, we now find ourselves in an age in which real-world

opted. This DID system is implemented on the second layer

entities are subject to being evaluated by various means.

of the Bitcoin blockchain, and source code has already been

From a management perspective, these measures may bereleased under the name ION (Identity Overlay Network)

necessary to ensure security, yet we still need a way to.

*43enable individuals to manage their own sensitive information
Finally, I will touch on credit scores and information banks.

based on the SSI concept. In particular, although it may

Some media reports claim services that calculate credit

not be easy to ask identity holders who have been issued ascores based on online activity are in the works in Japan

DID or claim for the first time to protect themselves in theas well. A concern is that only scoring done under the aus-

ways required, I think the ability to do this really is part ofpices of big-brother entities like GAFA and FAANG would be

the basic literacy we all need as denizens of the digital age.

considered accurate, and that your score could be passed
around without you intending it. As with AI, another talking

Some people have a desire to pass their social media ac-

point of late, there is a need to ensure transparency of notcounts to their children or grandchildren after they die, but

only the scoring system but the scoring algorithm as well.

this is becoming less and less advisable from a business*39

Microsoft Security Blog, “Decentralized identity and the path to digital privacy” (https://www.microsoft.com/security/blog/2019/05/15/decentralized-identity-digital-privacy/).

*40

Azure Active Directory Identity Blog, “Toward scalable decentralized identifier systems” (https://techcommunity.microsoft.com/t5/AzureActive-Directory-Identity/
Toward-scalable-decentralized-identifier-systems/ba-p/560168).

18

*41

Microsoft Whitepaper, Decentralized Identity—Own and control your identity (https://query.prod.cms.rt.microsoft.com/cms/api/am/binary/RE2DjfY).

*42

Decentralized Identity Foundation (DIF) (https://identity.foundation/) (https://github.com/decentralized-identity/).

*43

ION (Identity Overlay Network) (https://github.com/decentralized-identity/ion/).

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2. Focused Research (1)continuity perspective. With the advance of AI, it seems,

mechanisms for the Internet-based distribution of informa-

the temporary or permanent deactivation of accounts as antion (including sensitive information) linked to real-world

act of censorship against posted content is having a major

entities. But we face a large problem here. Privacy regula-

impact. I think these sorts of “everyday” examples are also

tions like the EU’s GDPR are not unique to the EU sphere.

a factor behind the rising call for services based on DID andCountries around the world, including Japan, are also sub-related technologies.

ject to such regulations. Hence, because the technologies
discussed here use blockchain and the circulation of cre-At present, I think a lot remains to be discussed in regard todentials is thus not limited to within any one region, use of

how we treat temporary IDs when it comes to handling mas-such technologies could face restrictions according to thesive quantities of statistical information and with respect

range of regulations that countries around the world have into cases in which credentials themselves are encrypted asplace. This is a far cry from the thinking behind cryptoassets​​

part of access control. A technology does not necessarilysuch as Bitcoin and Ethereum, and could be a major factor

gain traction just because the background technologies are

impeding the penetration of such technologies. The ERC-

compatible and it would have social applicability if deployed

725 Alliance and ID2020 will need to undertake activities

adroitly, and I have seen this many times over the years.

to dispel these impediments to cross-country distribution

At this juncture, it is uncertain whether the technologies I

mechanisms. At present, though, no such activities ap-

have discussed here will be deployed in applications users

pear to be underway. We need experts that can offer deep

identify with and be of any use to the world.

insights and broad perspectives to address these issues, including the issue of whether such problems should be dealt

With the advent of real use cases such as information banks,with by these consortiums in the first place.

people have come to realize the convenience provided by

Yuji Suga
Senior Engineer, Office of Emergency Response and Clearinghouse for Security Information, Advanced Security Division, IIJ. Dr. Suga has been in his current position since July
2008. He is engaged in investigation and research activities related to cryptography and information security as a whole. He heads up the CRYPTREC Operational Guidelines
Working Group on TLS Configuration and is a member of the CRYPTREC Cryptographic Technology Promotion Committee. He also serves as secretariat of the Cryptographic
protocol Evaluation toward Long-Lived Outstanding Security Consortium (CELLOS); secretary of the Information Processing Society of Japan’s Computer Security Group (CSEC);
assistant secretary of the ISEC Technical Committee of the Institute of Electronics, Information and Communication Engineers (IEICE); CyberSciTech2019 program co-chair;organizing committee member for IWSEC2019; and member of the Cryptoassets Governance Task Force (CGTF) Security Working Group.

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