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A First Look at Identity Management Schemes on the Blockchain


Abstract and Figures

The emergence of distributed ledger technology (DLT) based upon a blockchain data structure, has given rise to new approaches to identity management that aim to upend dominant approaches to providing and consuming digital identities. These new approaches to identity management (IdM) propose to enhance decentralisation, transparency and user control in transactions that involve identity information; but, given the historical challenge to design IdM, can these new DLT-based schemes deliver on their lofty goals? We introduce the emerging landscape of DLT-based IdM, and evaluate three representative proposals: uPort; ShoCard; and Sovrin; using the analytic lens of a seminal framework that characterises the nature of successful IdM schemes.
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A First Look at
Identity Management Schemes
on the Blockchain*
Paul Dunphy and Fabien A. P. Petitcolas,
Innovation Centre,
VASCO Data Security
Abstract. The emergence of distributed ledger technology (DLT) based upon a
blockchain data structure, has given rise to new approaches to identity management
that aim to upend dominant approaches to providing and consuming digital identi-
ties. These new approaches to identity management (IdM) propose to enhance de-
centralisation, transparency and user control in transactions that involve identity in-
formation; but, given the historical challenge to design IdM, can these new DLT-
based schemes deliver on their lofty goals? We introduce the emerging landscape
of DLT-based IdM, and evaluate three representative proposals uPort, ShoCard
and Sovrin using the analytic lens of a seminal framework that characterises the
nature of successful IdM schemes.
Keywords: Distributed Ledger Technology; Identity and Access Management.
1 Introduction
Twenty-four years have passed since Peter Steiner first showed the world that “on the
Internet, nobody knows you’re a dog”, yet that famous drawing still stands to illustrate
the challenge to identify individuals online. Today, we are very far from the public
directory vision of the inventors of public-key cryptography in the seventies or the
grand scheme of hierarchical certification envisaged in the eighties. Identity manage-
ment (IdM) on the Internet still relies on what Cameron [1] called a decade ago a
“patchwork of identity one-offs” comprising several types of IdM systems that are re-
stricted to specific domains and do not interact much with each other. Centralised mod-
els of IdM currently face challenges due to the increasing regularity of data breaches
that lead to reputation damage, identity fraud, but above all a loss of privacy for all
concerned. These recurring events highlight a lack of control and ownership that end-
users experience with their digital identities [2][4].
The investigation of alternative approaches to IdM is being led by initiatives that
seek to expand the trustworthiness and reach of digital forms of identity. The United
States’ National Strategy for Trusted Identities in Cyberspace (NSTIC) aims to accel-
erate the development of novel technologies that can increase trust in online transac-
tions [5]. Also, ID2020 seeks to leverage emerging digital technologies to expand the
* To appear in IEEE Security and Privacy Magazine special issue on “Blockchain Security and Privacy” in 2018
reach of legal identities (mirroring the United Nationsgoals to provide [by 2030]
legal identity for all, including birth registration [6]). The emergence of Bitcoin [7]
has also inspired fresh thinking about digital identity due to its underpinning distributed
ledger technology (DLT) not needing a central authority to validate transactions of its
native cryptocurrency. Thus, a globally decentralised network is able to reach
consensus on the current state of its book of transactions, theledger”. The distributed
ledger itself is an append-only shared record of transactions that is maintained by en-
tities on a peer-to-peer network; while the often-citedblockchain is a cryptographic
data structure often employed in DLT that is constructed through successive crypto-
graphic hashing of blocks of transactions.
Given that DLT is suited to assuring consensus, transparency, and integrity of the
transactions that it contains, a number of benefits of applying DLT to IdM have already
been proposed:
Decentralised – Identity information is referenced in a ledger that no single central
authority owns or control.
Tamper-resistantHistorical activities in the DLT cannot be tampered with and
transparency is given to all changes to that data.
Inclusiveness – New ways to bootstrap user identity can be conceived that expand
the reach of legal identities and reduce exclusion.
Cost saving – Shared identity information can lead to cost savings for relying par-
ties along with the potential to reduce volume of personal information that is repli-
cated in databases.
User controlUsers cannot lose control of their digital identifiers if they lose ac-
cess to the services of a particular identity provider/broker.
But, given these proposed benefits of incorporating DLT into future IdM schemes, is
the path to new forms of DLT-based IdM reallyinevitable” [2]?
2 Identity management on the blockchain?
Identity Management (IdM) encompasses the processes and policies involved in man-
aging the lifecycle of attributes in identities for a particular domain [8]. Most IdM
schemes today are centralised where a single entity controls the system. However, the
generated identities themselves can be federated beyond a single organisation, as when
governments issue national identity cards. In federated identity systems, users can use
identity information established in one security domain to access another. Single sign-
on schemes, such as Facebook Connect, can work this way. User-centric identity man-
agement places administration and control of identity information directly into the
hands of individuals. Examples include password managers (e.g., 1Password, Less-
Pass) that securely keep track of different website credentials.
Despite the different approaches, one function that is fundamental to IdM is securely
binding together an identifier: a value that unambiguously distinguishes one user from
another in a domain; and attributes (sometimes called certifications or claims): entitle-
ments or properties of a user such as name, age, credit rating etc. The first steps taken
to tailor the use of DLT for establishing a secure and decentralised identifier-attribute
mapping were taken in the design of Namecoin: the longest surviving software fork of
Bitcoin. Namecoin provides a human-readable, decentralised and secure namespace for
the .bitweb domain. This achievement contradicted conventional wisdom that a nam-
ing system exhibiting all three characteristics could not be designed [9]. Blockstack [4]
has extended Namecoin’s scheme, to create a decentralised public key infrastructure
(PKI): it registers bindings between a public key and a human readable identifier.
Recently, several decentralised identity schemes have emerged that extend beyond
naming and aim to provide a more complete suite of IdM functions. However, until
now, there has been no evaluation of these proposals. We were interested in whether
DLT-based IdMs have potential to go beyond previous approaches, or would simply
create new “identity one-offs”.
2.1 Approach
We started our inquiry by searching for blueprints of DLT-based IdM proposals that
were technically scrutable (e.g., white papers, open source software, etc.). We excluded
schemes that only provided naming and found that all fell into one of two categories:
1 Self-sovereign Identity: an identity that is owned and controlled by its owner with-
out the need to rely on any external administrative authority and without the pos-
sibility that this identity can be taken away. It can be enabled by a decentralised
identity eco-system that facilitates the recording and exchange of identity attrib-
utes, and the propagation of trust among participating entities. Examples include
Sovrin, uPort and OneName;
2 Decentralised Trusted Identity: an identity that is provided by a centralised service
that performs identity proofing of users based upon existing trusted credentials
(e.g. passport), and records identity attestations on a DLT for later validation by
3rd parties. Examples include ShoCard, BitID, and IDchainZ.
In this paper, we focus on three particular DLT-based IdM schemes: uPort, ShoCard,
and Sovrin. We chose these three schemes in particular because individually they serve
as key exemplars of the prevalent design decisions and challenges found in their re-
spective genres, and together serve a similar purpose for the broader landscape of DLT-
based IdM. In addition, they have provided the most technical detail of their scheme
designs and are either underpinned by sizeable online communities or have notable
venture capital funding.
There is no definitive criterion to evaluate IdM schemes, so in order to generate early
insights about individual schemes we leveraged an evaluation framework known as the
laws of identity[1] which serve to pinpoint the successes and failures of digital iden-
tity systems. It is a widely-known framework, and represents a full spectrum of IdM
concerns, encompassing security, privacy and user experience. Furthermore, the laws
provide an inherent flexibility, which is ideal for application to the heterogeneous and
early-stage DLT-based IdM schemes we evaluated. The laws themselves are as follows:
1 User control and consent Information that identifies the user should only be
revealed with that user’s consent.
2 Minimal disclosure for a constrained useIdentity information should only be
collected on a need-to-knowbasis and kept on a “need-to-retain” basis.
3 Justifiable parties – Identity information should only be shared with parties that
have a legitimate right to access identity information in a transaction.
4 Directed identity Support should be provided for sharing identity information
publicly or in a more discreet way.
5 Design for a pluralism of operators and technology – A solution must enable
the inter-working of different identity schemes and credentials.
6 Human integrationThe user experience must be consistent with user needs and
expectations so that users are able to understand the implications of their interac-
tions with the system.
7 Consistent experience across contextsUsers must be able to expect a consistent
experience across different security contexts and technology platforms.
In the text that follows, where we refer to a specific law, we use bracket notation to
reference the law number (e.g., (1), (5)).
3 uPort
uPort [3] is an open source decentralised identity framework that aims to provide de-
centralised identity for all. Its use case is IdM for next generation decentralised appli-
cations (DApps) on the Ethereum DLT and for traditional centralised applications such
as email and banking.
3.1 Design
A uPort identity is underpinned by the interactions between Ethereum smart contracts:
bespoke code that can regulate the movement of data and ether (the native cryptocur-
rency) on Ethereum. Smart contracts are uniquely addressed by 160-bit hexadecimal
identifiers, and, when invoked are executed by the Ethereum Virtual Machine (EVM)
installed on every Ethereum node. Two smart contract templates designed by uPort
comprise each uPort identity: controller and proxy. To create a new identity, a user’s
uPort mobile application creates a new asymmetric key pair and sends a transaction to
Ethereum that creates an instantiation of a controller that contains a reference to the
newly created public key. Then, a new proxy is created that contains a reference to the
address of the just-created controller contract; only the controller contract can invoke
functions of the proxy; a constraint that is specified in the controller and enforced by
the EVM. The address of the proxy comprises the unique uPort identifier (uPortID) of
a user. A user is free to create multiple uPortIDs that are unlinkable. Figure 1 provides
an overview of an interaction between a uPortID and the smart contract of a decentral-
ised application on Ethereum.
The private key that controls a uPortID is stored only on the user’s mobile device.
Therefore, an important aspect of uPort relates to its social recovery protocol for the
event of loss or theft of the user’s mobile device. For that, users must nominate the
uPortIDs of trustees who can vote to replace the public key referenced in the controller
with one proposed by the user in need; once a quorum is reached between those trustees
on the new public key, the controller replaces the lost public key with the newly pro-
posed public key. This process enables the user to maintain a persistent uPortID even
after the loss of cryptographic keys.
A final aspect of the uPort scheme is its support for securely mapping identity attrib-
utes to a particular uPortID. The uPort registry is a smart contract that stores the global
mapping of uPortIDs to identity attributes. Any entity can query the registry, however,
only the owner of a specific uPortID can modify its respective attributes. Due to the
inefficiency of storing large volumes of data in a smart contract, only the hash of the
JSON attribute structure is stored in the registry. The data itself is stored on IPFS: a
distributed file system where a file can be retrieved by its cryptographic hash.
3.2 Analysis
uPort has no central server and does not authenticate the owner of a uPortID; this passes
the risk of unauthorised access to the local authentication methods on the user’s mobile
device. While the social recovery protocol provides one method to recover ownership
of a lost or compromised uPortID, the trustees themselves could be one vector of attack
since their own uPortIDs are openly linked to the user’s uPortID; this transparency
provides opportunities for collusion against a specific uPort user. If an attacker can
compromise a uPort application and replace trustees unnoticed via the controller, the
uPortID is compromised permanently. So while uPort does place more control over
uPortIDs in the hands of its usersa plus for (1)a layer of added complexity and
responsibility is inevitably handed to users.
uPort does not require personal data disclosures to bootstrap an uPortID for a con-
strained use and also respects privacy in terms of the lack of inherent linkability be-
tween uPortIDs (2). However, the registry (if used) represents a point of centralisation
that can be probed for information about identifiers and identity data. So while specific
attributes within the attribute data structure can be individually encrypted, the overall
JSON data structure is still visible which could leak meta-data about specific attributes
or relationships with identity providers/relying parties. Thus there is a chance that over-
reliance upon the registry can compromise privacy (3).
A commerce application can widely advertise its uPortID, but uPort provides no
public directory to look up uPortIDs from arbitrary search criteria. Discreet disclosure
of a uPortID is possible if a user creates new uPortIDs for each new relying party that
they encounter and avoids the use of the registry (4). Although, since a uPortID equates
to a smart contract, an honest but curious Ethereum node could discover even non-
disclosed uPortIDs through analysis of the smart contract code stored at a given address
to determine if it is a uPort template. More work is needed to discover whether non-
disclosed uPortIDs are private in practice.
uPort does not perform any identity proofing but instead provides a framework for
users to gather attributes from an eco-system of trust providers; uPort simply specifies
the format of attributes that are stored in its registry. But as a consequence of the uPor-
tID owner alone having write-access to their own respective part of the registry, a user
can selectively discard negative attributes that they are given e.g. a poor credit score
etc. (5).
The mobile application of uPort provides a consistent user experience across all us-
age contexts (7) due to the scanning of a QR code to initiate interactions with a relying
party. However, the in-app education is not present relating to the implications of put-
ting representations of personally identifiable information on a DLT designed to prior-
itize immutability and transparency of data (6). The area of user education will become
pressing in this context as legislation such as European General Data Protection Regu-
lations (GDPR) come into force in Europe.
Figure 1: An overview of key elements of uPort: a user identity is comprised of a mobile
application and two smart contracts: controller and proxy. The registry is a smart contract
that provides a decentralised mapping of uPort identifiers to identity attributes. The regis-
try can be globally read, and can reference data stored in an off-DLT data store such as
4 Sovrin
Sovrin [2] is an open-source decentralised identity network built on permissioned DLT.
Sovrin is public, but only trusted institutions, called stewardswhich could be banks,
universities, governments, etc. can run nodes that take part in consensus protocols:
thus the ledger is permissioned. The non-profit Sovrin Foundation ensures the proper
governance of the stewards and their respect of a legal agreement called the Sovrin
Trust Framework. Sovrin provides the code-base to the Hyperledger Indy project.
Proxy ServiceController Calls Calls
Read/ write
Ethere um blockchain
4.1 Design
Sovrin enables a user to generate as many identifiers as needed to keep contextual sep-
aration of identities for privacy purposes; each identifier is unlinkable and controlled
by a different asymmetric key pair. Sovrin identifiers themselves are managed by the
user or an appointed guardian service, and follow the Decentralised Identifier (DID)
specification currently seeking IETF standardisation. A DID is a data-structure con-
taining the user identifier, cryptographic public key and other meta-data necessary to
transact with that identifier.
The Sovrin architecture can be summarised by the components as shown in Figure 2.
The key element is the Sovrin ledger. This contains transactions associated with a spe-
cific identifier and is, written, distributed and replicated among the steward nodes,
which run an enhanced version of the redundant Byzantine fault tolerant protocol of
Aublin et al. [10], called Plenum, for consensus.
There are two important consequences to the choice of permissioned ledger in Sov-
rin’s design. First, no expensive proof-of-work computation is required to reach con-
sensus on the state of the ledger, reducing significantly the energy cost of running a
node and improving dramatically transactions throughput. Second, trust on Sovrin re-
lies on both people and code. Trust starts from the common root-of-trust formed by the
globally distributed ledger, but as new organisations and users join the network, they
can become trust anchors (i.e. allowed to add more users and organisations); a “web of
trust” is expected to evolve to support this decentralised network growth.
Users interact with Sovrin through a mobile application and control software agents
acting on their behalf to facilitate interactions with other agents on the network. Agents
are network endpoints that are always addressable and accessible. Users could run
agents on their own servers, but more likely, they will ask specialised intermediaries:
agencies, to do that for them, alike e-mail systems. Agents also provide a backup ser-
vice and encrypted storage of attribute credentials.
The mobile application also helps users manage cryptographic keys, which are stored
on the users’ mobile device. As in uPort, Sovrin offers a mechanism for key recovery
that relies on the user selecting a set of trustees. When requested to do so by the user, a
specified quorum of trustees must sign a new identity record transaction that stewards
must verify.
4.2 Analysis
Sovrin aims to equip users to fully control all aspects of their identity. Each user can
select from the attribute credentials that they hold about themselves, which they wish
to share with a relying party (1). This is made possible through the use of anonymous
credentials. Although users can choose to store those attributes on the ledger, in general,
they will prefer to use the storage capabilities of their mobile phone or their agent to
transmit attributes to other parties through secure communication channels, and use the
ledger to identify the correct network endpoint to use. The use of attribute-based cre-
dentials allows users to only reveal credentials that they choose (2). Verifying the party
with whom data is shared, remains a challenge, which is partly addressed through the
web-of-trust, the governance of the Sovrin Foundation and the reputation of the stew-
Although there are no trusted third parties in the PKI-sense on Sovrin, users must
rely on agencies that will act on their behalf on the Sovrin network and on the stewards
maintaining the ledger. Depending on the choice of agent and its implementation, a lot
of information could potentially be in the hands of the agency. However, as agencies
are acting on behalf of the user, they have a necessary and justifiable place in the
identity relationship (3).
Sovrin supports both omnidirectional and unidirectional identifiers (4): public or-
ganisations can decide to publish their full identity on the network, while users may
choose to publish only identifiers and to use different identifiers and cryptographic key-
pairs with each party they interact with, avoiding emitting correlation handles”.
Today, Sovrin depends on a very small number of operators sharing the same imple-
mentation. As the systems gets traction, new agencies, and new stewards, will join. The
Sovrin Foundation expects in particular to build a market of agencies that will compete
on the features they offer, for instance interfaces with other (existing) identity sys-
tems (5).
Finally, one important issue not yet addressed by the Sovrin developers, is the user
experience. The history of security offers several examples of smart cryptographic sys-
tems, which have never been deployed widely because users found it too cumbersome
or difficult to understand email encryption using PGP is a seminal example. So, hu-
man integration remains an open question for Sovrin. Considering that Sovrin is still in
the early development phase, evaluating it against laws (6) to (7) is tricky, but it is
illustrative that much work has considered the design of the scheme architecture itself,
but hardly any has considered the user experience.
Figure 2: An overview of key elements of Sovrin. At the base of Sovrin is a permissioned
ledger. Only stewards that legally abide by the Sovrin Trust Framework can write to the
ledger. Users and organisations rely on agents that are addressable network points. Identi-
fiers, keys and endpoint addresses are stored on the ledger.
5 ShoCard
ShoCard [11] provides a trusted identity that leverages DLT to bind a user identifier,
an existing trusted credential (e.g., passport, driver’s license), and additional identity
attributes, together via cryptographic hashes stored in Bitcoin transactions. ShoCard’s
primary use cases are verification of identity in face-to-face as well as online interac-
5.1 Design
ShoCard uses Bitcoin as a timestamping service for signed cryptographic hashes of the
user’s identity information, which are mined into the Bitcoin blockchain. ShoCard in-
corporates a central server as an essential part of its scheme; this server intermediates
the exchange of encrypted identity information between a user and a relying party. The
scheme relies on three phases: bootstrapping, certification, and validation. Figure 3
schematises those phases.
Bootstrapping occurs at the creation of a new ShoCard. The ShoCard mobile appli-
cation generates a new asymmetric key pair for the user and scans their identity cre-
dentials using the device’s camera. The scan and the corresponding data are encrypted
and stored on the mobile device; the signed hash of this data is also embedded into a
Sovrin ledg er
ID s ,%keys,%end-point%addresses
Controls Us er
User ( U) a gent
Data vault Policy & keys
Ledger client
Service provider ( S) a gent
Data vault Policy & keys
Ledger client
Direct communicatio n
Read/ write
Bitcoin transaction for later data validation purposes. The resulting Bitcoin transaction
number constitutes the user’s ShoCardID and is retained in the mobile application as a
pointer to the ShoCard seal
Once a ShoCard is bootstrapped, the user can interact with identity providers to
gather additional attributes in a process called certification. In order to associate certif-
icates to a ShoCardID, an identity provider must first verify that the user knows both
the data hashed to create it, and the cryptographic keys that signed the seal. In a face-
to-face context, this can be achieved by the user providing the original identity data
forming the seal from their mobile device, a digitally signed challenge and presenting
the original trusted credential. The certificate takes the form of a signed hash of new
attributes (and its associated ShoCardID) in a Bitcoin transaction created by the pro-
vider. The provider must share the Bitcoin transaction number along with a signed
plaintext of the new attributes directly with the user. Since the user will later need to
provide the attributes to relying parties and may not want to lose them if the mobile
device is lost, a ShoCard server offers storage for encrypted version of certifications
(known as an envelope). ShoCard never learns the encryption key, which enables the
user to share certifications only with selected parties.
The validation phase occurs when a relying party must verify a certification to de-
termine whether a user is entitled to access a service (e.g. has checked in to a flight).
To validate the envelope the user must first provide the relying party with the envelope
reference and its encryption key. After retrieving the envelope from the ShoCard serv-
ers, the relying party performs a number of checks: i) that the envelope signature was
produced with the same private key that signed the seal; ii) that the certification signa-
ture was created by a trusted entity and the plain-text certification corresponds to the
one hashed and signed in the certification; iii) finally, that the identity data presented
by the user in the pending transaction match those signed and hashed in the seal.
5.2 Analysis
The ShoCard central server functions as an intermediary to manage the distribution of
encrypted certifications between ShoCard users and relying parties. In this way, Sho-
Card bears less risk of data breach than if it stored and distributed plaintext identity
data. Secure storage of identity information and appropriate sharing with relying parties
is controlled by the end-user (1). However, ShoCard’s intermediary role does create
uncertainty about the longitudinal existence of a ShoCardID; if the company ceased to
exist, users of ShoCard would be unable to use the system with the certifications they
had acquired. This makes ShoCard more centralised in practice than its open reliance
on DLT might suggest.
Each ShoCard identity is bootstrapped with an existing trusted credential, such as a
passport or driving license. Such an approach may require users to embed more per-
sonal information in their ShoCard seal than they had originally intended. This may
make ShoCard less attractive for low value online accounts (2).
Since the user is in control of initiating sharing activities, and since ShoCard only
stores encrypted data, there can be some confidence that only justifiable parties are
involved in the identity data sharing transaction. However, the ShoCard server may be
able to associate a particular ShoCardID with a particular relying party, since envelopes
must be retrieved from ShoCard server by the relying party (3).
ShoCard only supports unidirectional identifiers and does not have the concept of a
public registry of ShoCardIDs. Although omnidirectional identifiers may be needed in
future to realise its vision of an eco-system of reusable certifications (4).
ShoCard does support a multitude of different identity providers through its certifi-
cation functionality, but those providers must create bespoke integration with Sho-
Card’s own web services in addition to Bitcoin, which could be a barrier to uptake. The
decision to perform such integration could be driven by the trustworthiness of Sho-
Card’s identity proofing of its users (5).
The scanning of identity documents and QR codes is a dominant interaction para-
digm in the ShoCard user experience: it is simple and consistent (7). However, it is
unclear what the user motivations would be to adopt this new type of digital identity,
and how users would be educated about the implications of referencing identity data on
a blockchain (6). Users are also not supported with cryptographic key management.
One final point concerns the overall deployability of ShoCard. Bitcoin transactions
take on average 10 minutes to be mined into the blockchain, and furthermore it is rec-
ommended to wait for six additional blocks to be mined before assuming the settlement
of a transaction. This could bring the waiting time for settlement to one-hour on aver-
age. If a context that depends upon real-time settlement of certifications, this speed
could create challenges for the user experience and adoption by vendors.
Figure 3: An overview of key elements of ShoCard. ShoCard uses Bitcoin to record a com-
mitment to personal data that was verified during identity proofing, and for storage of
hashes of certifications that build upon the user’s Seal created by relying parties. The Sho-
Card server plays an active role as an intermediary between users and relying parties.
6 Discussion
Table 1 summarizes each scheme that we evaluated with respect to each law of identity.
An unshaded table cell indicates that we found evidence that suggests a scheme com-
plied with a specific law, and a shaded cell indicates that we didn’t find evidence that
Create Seal
Create Certification
Envelope reference + Plain text identity
Bit coin blockchain
Prove seal ownership
Retrieve envelope
Read certification
& se al
SealT rans. # CertificationT rans. #
Identity Proofing
suggested compliance with a specific law. We additionally include a summary of Fa-
cebook Connect to provide contrast.
6.1 Decentralisation that relies upon centralisation and intermediaries
DLT is often seen as a remedy for system architectures dominated by central authorities
and intermediaries. But while each DLT-based IdM scheme we looked at leverages
techniques of decentralisation to different degrees, this served mainly to reshape the
role of centralisation and intermediaries, rather than to eradicate them. For example,
uPort’s registry stores a secure mapping between uPortID and their attributes and also
relies upon central authorities as trust providers for identity attributes; the ShoCard
central server is an intermediary that stores encrypted identity attributes and mediates
between end-users and relying parties. Sovrin on the other hand embraces an open eco-
system of intermediaries (e.g., agencies, trust anchors).
So, while DLT applications often target the removal of the middle man”, this may
not be a realistic goal in IdM applications due the context of identity maintaining a
profound need for trust. Of course, this need for centralisation and intermediaries is not
necessarily a bad thing: there are numerous examples of centralisation and intermedi-
aries serving essential functions in an industry (see e.g., the SWIFT network). Elements
of needed centralisation or intermediation in a decentralised IdM may comprise:
Capturing additional authentication factors from end-users;
Backing-up and recovering cryptographic keys;
Providing a secure namespace to facilitate lookup of entities and services;
Storing securely the information hash pre-images needed to validate digital signa-
Recovering compromised DLT-based identities.
The case of “The DAO” stands as an example of the risks of pursuing too much decen-
tralisation in a system design. The DAO was designed as an Ethereum smart contract-
based autonomous venture capital company but a flaw in its underlying code enabled
an attacker to steal $50 million of the funding that it collected [12]. The research chal-
lenge for DLT applications in IdM is therefore to explore the balance between central-
isation and decentralisation to create interoperable and privacy-respecting IdM that mit-
igates the risk of placing too much trust in any single authority.
6.2 Envisioned eco-systems of shareable identity attributesbut ad hoc trust
Support for the creation and sharing of identity attributes certified by 3rd parties is a
design feature of each scheme we evaluated. In ShoCard, 3rd parties can certify attrib-
utes of an identifier; uPort and Sovrin support both self-attestation of attributes and
those assigned by other entities.
Designing for reusable identity attributes aims to improve the granularity at which
users can disclose identity information and promotes reuse of attributes. However, due
to the lack of a central authority, trust of these attributes currently relies upon ad-hoc
trust establishment between organisations. ShoCard and Sovrin propose a web of
trustas the means by which attributes can be trusted. However, the challenges to de-
sign a web-of-trust are widely known where the network size is unbounded: difficulty
to quantify trust beyond a first-degree relationship especially if any entity can vouch
for any other, poor density of trust anchors on the network, lost or expired private keys,
slow propagation of endorsement between users, etc. DLT does not address any of those
challenges, but future research could focus on methods to achieve the building of trust
and reputation between entities in the context of DLT identity attributes. This could be
one way that DLT-based IdM responds to NSTIC [5] and delivers new interoperability
in IdM.
6.3 If it isn’t usable it isn’t secure
Dhamija’s explains in her 7 flaws of identity management” [13] that for users identity
management is not a primary goal”. This has been reflected in the shrug that users have
largely given to single-sign on solutions: the main user-facing proposition of IdM. This
suggests that future IdM schemes with a novel technological underpinning but devel-
oped to the same blueprint of end-user interaction are unlikely to create widespread
uptake. A principal tenet of human-computer interaction is to design systems based
upon concrete knowledge of problems faced by end-users. So far we have seen that the
schemes we evaluated are generally not accompanied by a novel vision of user interac-
tion, and furthermore leave the perennial challenge to provide usable end-user key man-
agement [14] as largely unaddressed. Recent research has suggested that key manage-
ment remains to be a principal source of concern for users of Bitcoin [15]. While the
promising concept of key recovery was proposed in uPort and Sovrin, approaches to
digital identity that remove central authorities and depend upon effective key manage-
ment strategies from its users create the risk that non-technical users will be alienated
by the technology; and when things go wrong those users will be unable to recover
resources or reputation attached to lost keys.
7 Concluding remarks
Distributed Ledger Technology (DLT) is not a silver bullet solution for Identity Man-
agement (IdM). Our application of Cameron’s evaluative framework provides an early
glimpse of the current strengths and limitations of applying DLT to IdM. Future work
in this nascent research area faces two particular hurdles:
Firstly, there is a noticeable lack of contextual understanding relating to the user
experience elements of the schemes we encountered. Usability is a particularly pressing
unknown since there appears to be a widespread assumption that users are equipped to
conduct effective cryptographic key management, and would intuitively understand the
implications of referencing identity data or attributes in a DLT.
Secondly, a tightening regulatory landscape for storing personal data. For example,
the General Data Protection Regulation (GDPR) grants end-users new powers over per-
sonal data, and places new obligations upon data controllers. This creates a challenge
for the design of immutable public ledgers that reference personal data, and that provide
inherent transparency to data that they store.
Delaying the advance of new approaches to secure and trusted identities on the In-
ternet was said to be an unacceptable course of action by the United States’ NSTIC
strategy [5]. This might be due to the concern that the online adage that on the block-
chain, nobody knows you’re a fridge”, may soon replace the prescience of Steiner’s
original cartoon.
Table 1: A summary of uPort, ShoCard, Sovrin, and their relation to Cameron’s laws of identity. Facebook Connect is provided for comparison. An unshaded table cell indicates that we found evidence that
a scheme complied with a specific law, and a shaded cell indicates that we currently see no evidence that a scheme complies with a specific law.
Facebook Connect
1 – User control and
User controls creation and disclosure of uPor-
tIDs and can prove ownership of uPortID with-
out a central authority. But attributes stored in
registry may leak information.
User controls creation and disclosure of ShoCar-
dIDs. Attributes are only accessible to a relying
party by invitation of ShoCardID owner. But,
ShoCard servers are necessary part of attribute
validation protocol.
By design, users can choose which IDs are used
and which attributes are revealed. A web of trust
that could be reinforced by a reputation system
helps protect users against deception.
Today, when using Facebook to log on to a ser-
vice the user can choose which data will be
shared by Facebook with the relying party.
2 – Minimal disclosure
for a constrained use
Users do not need to disclose personal data in
order to create uPort identifiers for low value ac-
ShoCardIDs are bootstrapped with a trusted
identity document (e.g., a government ID).
Support of anonymous credentials based on
zero-knowledge proofs allows users to share the
information “least likely to identity [them]
across multiple contexts” [1].
A user can create an empty Facebook profile and
progressively add identity information as is
3 – Justifiable parties
The JSON structure of attributes in the registry
is visible to all, which may leak information to
an honest-but curious attacker even if en-
ShoCardID only revealed to a relying party at
the invitation of the ShoCardID owner. ShoCard
servers may learn identity of relying parties.
Attributes are only accessible to relying parties
that the user chooses, and to the agencies en-
trusted to act on their behalf.
Facebook always has access to the data stored on
a user’s Facebook profile whether the data is
public or private. Facebook also creates and pro-
cesses its own attributes e.g. relationships with
4 – Directed identity
Supports unidirectional sharing of identifiers be-
tween parties, but does not prevent entities
broadcasting identifiers out of band e.g. on web-
Supports unidirectional sharing of identifiers be-
tween parties, but does not prevent entities
broadcasting identifiers out of band.
Omnidirectional identifiers are supported.
Omnidirectional identifiers are supported. A
user’s Facebook profile can be made public or
private and profiles can be searched.
5 – Design for a plural-
ism of operators and
Agnostic to the types of attributes that 3rd party
identity providers create, yet use of a specific
data format is encouraged in the registry.
Supports parsing of existing trusted credentials
but relying parties must create bespoke integra-
tions with ShoCard centralised servers for attrib-
ute validation.
Expects to build a market for intermediaries
(agencies) between users and the Sovrin net-
work. Some could be interfaces with other iden-
tity systems.
Only one identity provider: Facebook. Uses a
bespoke method for authorisation to applica-
tions. But, Facebook has nearly 2 billion users.
6 – Human integration
Provides a mobile application. Social crypto-
graphic key recovery function shows promise.
Unclear usability and user understanding of
uPort privacy implications.
Provides a mobile application. The digital ID
card metaphor is easy to understand. Unclear us-
ability and user understanding of ShoCard pri-
vacy implications.
Implementation has been targeted so far towards
the underlying technology, not the user experi-
ence. Unclear usability and user understanding
of privacy.
Facebook is well known to users and usable in-
terface to single-sign is provided. However, us-
ers may be unaware of privacy implications of
Facebook Connect.
7 – Consistent experi-
ence across contexts
User interaction driven by the mobile applica-
tion. Consistently follows a QR code scanning
paradigm for all uses.
User interaction driven by the mobile applica-
tion. Consistently follows a QR code scanning
paradigm for all uses.
Not clear. This will highly depend on the market
of implementations of mobile device clients for
the Sovrin network.
Consistent and experience via the ‘login with Fa-
cebook’ button.
[1] Kim Cameron, ‘The Laws of Identity’. Microsoft Corporation, 05-Nov-2005.
[2] Andrew Tobin and Drummond Reed, ‘The Inevitable Rise of Self-Sovereign Identity’.
The Sovrin Foundation, 29-Sep-2016.
[3] Christian Lundkvist, Rouven Heck, Joel Torstensson, Zac Mitton, and Michael Sena,
uPort: A Platform for Self-Sovereign Identity’. 21-Feb-2017.
[4] Muneeb Ali, Jude Nelson, Ryan Shea, and Michael J. Freedman, ‘Blockstack: A Global
Naming and Storage System Secured by Blockchains’, in 2016 USENIX Annual Technical
Conference (USENIX ATC 16), Denver, CO, 2016, pp. 181194.
[5] The White House, ‘National Strategy for Trusted Identities in Cyberspace: Enhancing
Online Choice, Efficiency, Security, and Privacy’, 2011.
[6] United Nations, ‘Transforming our world: the 2030 agenda for sustainable development’,
[7] Satoshi Nakamoto, ‘Bitcoin: A peer-to-peer electronic cash system’. 2008.
[8] ‘ISO/IEC 24760-1 Information technology Security techniques A framework for
identity management Part1: Terminology and concepts’. ISO/IEC, 2011.
[9] Zooko Wilcox-O’Hearn, ‘Names: Distributed, Secure, Human-Readable: Choose Two’.
[10] Pierre-Louis Aublin, Sonia Ben Mokhtar, and Vivien Quéma, ‘RBFT: Redundant Byzan-
tine Fault Tolerance’, in Distributed Computing Systems (ICDCS), 2013 IEEE 33rd In-
ternational Conference on, 2013, pp. 297306.
[11] ‘Travel Identity of the Future White Paper’. SITA; ShoCard, May-2016.
[12] ‘Not-so-clever contracts’, The Economist, 30-Jun-2016.
[13] Rachna Dhamija and Lisa Dusseault, ‘The Seven Flaws of Identity Management: Usabil-
ity and Security Challenges’, IEEE Secur. Priv., vol. 6, no. 2, pp. 2429, Mar. 2008.
[14] Alma Whitten and J. Doug Tygar, ‘Why Johnny Can’t Encrypt: A Usability Evaluation
of PGP 5.0.’, in 8th USENIX Security Symposium, 1999, pp. 169183.
[15] Shayan Eskandari, David Barrera, Elizabeth Stobert, and Jeremy Clark, ‘A First Look at
the Usability of Bitcoin Key Management’, presented at the NDSS Workshop on Usable
Security 2015 (USEC 2015), San Diego, California, 2015.
Paul Dunphy is the lead researcher on the distributed ledger technology research
theme at VASCO Data Security, based at their Innovation Centre in Cambridge, UK.
Prior to joining VASCO he spent time at Atom Bank: the UK’s first bank to deliver
services entirely via mobile applications that pioneered the use of mobile biometrics.
He joined during Atom’s start-up phase and shaped the successful first launch of its
mobile applications, which in total have processed close to £1 billion in customer de-
posits. He completed a Microsoft Research funded PhD at Newcastle University (UK)
where his thesis focused on usable, secure and deployable user authentication. He has
also spent time leading research projects at Microsoft Research and Nokia Research.
His research interests are broadly at the intersection of privacy and security with hu-
man-computer interaction.
Fabien Petitcolas is research manager at VASCO Data Security, where he is contrib-
uting to grow and lead the recently established VASCO Innovation Centre. Prior to
joining VASCO, Fabien spent fifteen years at Microsoft where he took various roles.
He first became a member of the Security Group at Microsoft Research where he fo-
cused on digital watermarking. He later became head of Microsoft Research’s intellec-
tual capital development programmes, before becoming director for innovation at Mi-
crosoft Europe, supporting the company’s presence in E.U. policy and political dia-
logue for and around innovation and R&D. Fabien received a PhD in computer science
from the University of Cambridge (U.K.) under the guidance of Prof. Ross Anderson
FRS FREng. His research interests include information hiding, an area where he has
authored several publications and books, and, more recently, security issues related to
identity management and user authentication.
... It was initially introduced as a tamper-proof decentralized ledger for prevention of double spending in cryptocurrencies like Bitcoin [39]. However, in recent years many new blockchain applications were developed, in a variety of areas, including supply chain management [21,58], healthcare [16], identity management [22], finance [56], transportation [31], management of personal data [62], tracking IoT devices [8] and managing drones [18]. Blockchain has become an important tool for managing shared data in applications with no agreed-upon trusted entity that could store and manage all the data, or when data records should result from a consensus between organizations that do not fully trust each other [26]. ...
... In cryptocurrencies like Bitcoin, transactions represent transfer of coins between addresses (aliases of users). In other blockchain applications, transactions can include financial information [56], health records [16], user identity information [22], IoT data [8], personal data [62], and records on parts of cellular devices. ...
... The centralized system is the model we have been using for a long time: government ID, license card, college identity card, voter ID, Facebook, Twitter login, and so on. The identity issuer (mainly government and service provider) issues the identifiers and credentials to the user in the centralized identity model [7,8]. ...
... SSI introduces a layer of flexibility and security in distributed identity management systems. SSI is the concept where organizations and individuals have whole ownership of their identities along with selfdefined attributes and identifiers, while the distributed identified management system (DIMS) uses the user's already existing trusted credentials like PAN, Voter ID, Passport, etc [7]. ...
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... By incorporating wellestablished research on the consumer perspective on eventticketing, we refrain from interviewing end users. However, we acknowledge that generic usability studies of SSI are an interesting future research endeavor (Dunphy & Petitcolas, 2018). Table 1 provides an overview over the experts and their backgrounds. ...
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A purely peer-to-peer version of electronic cash would allow online payments to be sent directly from one party to another without going through a financial institution. Digital signatures provide part of the solution, but the main benefits are lost if a trusted third party is still required to prevent double-spending. We propose a solution to the double-spending problem using a peer-to-peer network. The network timestamps transactions by hashing them into an ongoing chain of hash-based proof-of-work, forming a record that cannot be changed without redoing the proof-of-work. The longest chain not only serves as proof of the sequence of events witnessed, but proof that it came from the largest pool of CPU power. As long as a majority of CPU power is controlled by nodes that are not cooperating to attack the network, they'll generate the longest chain and outpace attackers. The network itself requires minimal structure. Messages are broadcast on a best effort basis, and nodes can leave and rejoin the network at will, accepting the longest proof-of-work chain as proof of what happened while they were gone.
Web identity management systems are complex systems with powerful features - and many potential vulnerabilities. They aim to facilitate the management of identifiers, credentials, personal information, and the presentation of this information to other parties. In many schemes, an identity provider (IdP) issues identities or credentials to users, while a relying party (RP) depends on the IdP to check the user credentials before it allows users access to Web site services. By separating the role of and IdP from the RP, identity management systems let users leverage one identifier across multiple Web services.
The Inevitable Rise of Self-Sovereign Identity'. The Sovrin FoundationuPort: A Platform for Self-Sovereign Identity'. 21-Feb
  • Andrew Tobin
  • Drummond Reed
Andrew Tobin and Drummond Reed, 'The Inevitable Rise of Self-Sovereign Identity'. The Sovrin Foundation, 29-Sep-2016. [3] Christian Lundkvist, Rouven Heck, Joel Torstensson, Zac Mitton, and Michael Sena, 'uPort: A Platform for Self-Sovereign Identity'. 21-Feb-2017. [4]
Why Johnny Can't Encrypt: A Usability Evaluation of PGP 5.0
  • Alma Whitten
  • J Doug Tygar
Alma Whitten and J. Doug Tygar, 'Why Johnny Can't Encrypt: A Usability Evaluation of PGP 5.0.', in 8th USENIX Security Symposium, 1999, pp. 169-183.
The Inevitable Rise of Self-Sovereign Identity'. The Sovrin Foundation
  • Andrew Tobin
  • Drummond Reed
Andrew Tobin and Drummond Reed, 'The Inevitable Rise of Self-Sovereign Identity'. The Sovrin Foundation, 29-Sep-2016.
Blockstack: A Global Naming and Storage System Secured by Blockchains
  • Muneeb Ali
  • Jude Nelson
  • Ryan Shea
  • Michael J Freedman
Muneeb Ali, Jude Nelson, Ryan Shea, and Michael J. Freedman, 'Blockstack: A Global Naming and Storage System Secured by Blockchains', in 2016 USENIX Annual Technical Conference (USENIX ATC 16), Denver, CO, 2016, pp. 181-194.
National Strategy for Trusted Identities in Cyberspace: Enhancing Online Choice, Efficiency, Security, and Privacy
  • The White House
The White House, 'National Strategy for Trusted Identities in Cyberspace: Enhancing Online Choice, Efficiency, Security, and Privacy', 2011.