Portable Personal Identity Provider in Mobile Phones
Md. Sadek Ferdous
School of Computing Science
University of Glasgow
School of Computing Science
University of Glasgow
Abstract—This paper analyses the prospect of having a
Portable Personal Identity Provider (PPIdP, in short) in the
mobile phone. The ubiquitous presence of powerful mobile
phones equipped with high speed networks can be utilised to
make the mobile phone act as a portable and personal Identity
Provider (IdP, in short) on behalf of their users. Such an IdP
would be helpful for the user in the sense that it will provide
a central location to manage different user attributes which
are generally scattered among different service providers in
the traditional setting of online services. In addition, the user
needs to trust the provider to store those attributes securely
which may not be always honoured and crucial user attributes
may be abused. Creating a Personal Identity Federation using
a personal IdP can tackle many of these stated problems.
Moreover, such an IdP may provide additional advantages. We
have developed such a Mobile IdP for the Android platform
based on the Security Assertion Markup Language (SAML)
and OpenID as a proof of concept using the Jetty Web Server.
In this paper, we discuss the functionalities of our developed
IdP and the technical challenges we have faced. Moreover, we
analyse the security, privacy and trust issues involved in having
such an IdP and the advantages it offers.
Keywords-Identity Management, Identity Provider, Feder-
ated Identity Management, Security Assertion Markup Lan-
guage, OpenID, Trust.
With the continuous evolution of web-enabled (or online)
services in the last decade or so, the way those services
can be accessed has changed considerably. As the number
of such online services as well as the user-base was ex-
panding rapidly, the management of user identities became
challenging, both for service providers and for users. Identity
Management (IdM, in short) was introduced by the industry
to facilitate online management of user identities which
resulted in various different Identity Management Systems
(IMS, in short). Formally, Identity Management consists of
technologies and policies for representing and recognising
entities using digital identiﬁers within a speciﬁc context .
Shibboleth , OpenID , Microsoft’s CardSpace , etc.
are all examples of different IMS.
Each IMS usually has three different actors: Identity
Provider (IdP) - an entity responsible for managing digital
identities of users and providing identity related services to
different Service Providers; Service Provider (SP) - an entity
to provide web-enabled services to the users based on the
identity information (identiﬁers and/or attributes) received
from the IdP and User (Client) - an entity that receives
services from a SP. Among different IMS, Federated Identity
Management (FIM, in short) System has gained considerable
attention. It is based on the concept of Identity Federation
(also known as Federated Identities or Federation of Identi-
ties). In the ITU-T X.1250 recommendation, a federation is
deﬁned simply as “An association of users, service providers
and identity providers” . In other words, a federation
with respect to Identity Management is a business model
in which a group of two or more trusted parties legally bind
themselves with a business and technical contract , .
It allows a user to access restricted resources seamlessly
and securely from other partners from different Identity
Domains. An identity domain is the virtual boundary, context
or environment in which a digital identiﬁer is valid .
Single Sign On (SSO) is the capability that allows users
to log in one system and then access other related but
autonomous systems, from the same or different identity
domains, without further logins.
(a) Type 1. (b) Type 2.
Figure 1. Federated Identity Domain.
A federated identity domain can be formed consisting of
only one IdP within an identity domain and more than one
SP with each SP residing in a separate identity domain (Type
1 in Figure 1). Several federated identity domains can be
combined to form a larger federated identity domain where
each smaller federated domain is of Type 1 (Type 2 in Figure
1). The issue of trust is a fundamental concept in FIM as
different autonomous bodies need to trust each other inside
the federation. Such parties inside a federation is said to
To appear in the Proceedings of The 12th IEEE International Conference on Trust, Security and Privacy in
Computing and Communications (IEEE TrustCom-13)
form the so-called Circle of Trust (CoT).
Most IMSs, including the FIM, have been designed to
help organisations to manage their user identities whereas
the management of user identities by the user is mostly over-
looked . This results in serious negative consequences.
Firstly, the user has limited control once the attributes are
stored in the IdP and has no way of knowing how these
attributes are handled at the IdP. Secondly, the management
of such attributes becomes increasingly difﬁcult for the user
once the number of IdPs starts increasing. The proposed
portable personal IdP can solve both problems.
Current mobile phones are equipped with powerful hard-
ware, intuitive software and advanced capabilities and are
rightfully called Smartphones. The ubiquitous presence of
such powerful mobile phones equipped with high speed
mobile networks enables users to access online services
literally everywhere. It makes them the suitable choice as
the host of the poratble personal IdP which we introduce in
this paper. The contributions of our paper are:
•Being a novel term, we, at ﬁrst, provide a concrete def-
inition of the term “Portable Personal Identity Provider
(PPIdP)” and “Personal Identity Federation”.
•We introduce the notion of Personal Attribute Store
(PAS) for mobile phones which can be used to store
crucial user attributes securely and will be used by the
PPIdP during a service access scenario.
•We describe our developed proof of concept of the PAS
and the PPIdP based on the Security Assertion Markup
Language (SAML)  and OpenID  to illustrate the
applicability of our approach. Note that there are other
IdM Protocols available such as WS-Federation ()
and OAuth , but in this paper, our main focus will
be on SAML and OpenID.
•Since SAML was not envisioned to be applied in such
a setting, many established trust assumptions do not
hold. Our approach requires formulating novel trust
assumptions. We analyse these trust issues in details
while describing our proof of concept.
•We also analyse different security and privacy issues
involved with our approach, the advantages it offers
and the limitations it has.
The reminder of this paper is organised as follows. We
discuss a few key works related to this topic and analyse
their strengths and weaknesses in Section II. The concept
of PPIdP and related issues are deﬁned in Section III. The
notion of the PAS is introduced and our developed proof of
concept of the attribute store and the PPIdP are discussed
in Section IV. Different security and privacy issues are
analysed in Section V and a discussion of advantages and
limitations along with the extensibility and future work of
our approach can be found in Section VI. We conclude in
II. RELATED WORK
Each mobile phone is equipped with a Subscriber Iden-
tiﬁcation (or Identity) Module (SIM) which stores a unique
International Mobile Subscriber Identity (IMSI) number and
the related cryptographic keys that are used to uniquely
identify and authenticate the user and then register the
SIM into the respective mobile network . In such,
the mobile operator can be used as the IdP using the
SIM as the facilitator and is commonly known as the
“Mobile Identity Management” . Several standards such
as Generic Authentication Architecture (GAA)  and
Generic Bootstrapping Architecture (GBA )  have been
put forward as part of the 3rd Generation Partnership Project
(3GPP)  to integrate such mobile identity management
with the existing web services. These standards allow to
leverage the strong authentication mechanism using SIM to
access services. The problem with this approach is that the
IdP (the mobile operator) controls all user attributes and the
user has no or limited control over the attributes. Moreover,
users often change mobile networks and/or the SIM meaning
that attributes stored with the previous operator may not be
used to access web services when the user has changed the
mobile network. For these reasons, we will not explore this
approach any further.
Being a novel topic, there have been relatively fewer
works related to the theme of this paper. The initial concept
of a Personal Identity Provider can be found in , in which
the authors proposed their idea of Identity-aware Devices.
An identity-aware device contains a local IdP hosted inside
a Trusted Platform Module (TPM) in the device. The local
IdP is coupled with a telecom provider which acts as the
principal IdP. Our approach is similar to this approach with
one major difference: their approach requires the user to rely
heavily on the principal IdP whereas we want to decouple
the reliance on any other external IdPs. Another work related
to our theme can be found in , in which a portable
Liberty Alliance1-enabled IdP installed in the mobile phone
is presented. The IdP is accompanied by a Relay Server
which is maintained by the Mobile Operator. However, this
paper does not discuss how the federation can be established
nor does it describe how user attributes will be transmitted to
the SP. In , the author proposes a type of device-centric
identity which allows a user to authorise a device to use
a cryptographic key to identify the user and then to allow
accesses to online services and user attributes. However, it is
not outlined how such a proposal can be realised in practice.
Current popular Smartphone Operating Systems such
as Android, iOS, Windows, etc. are associated with
their respective IdPs. For Android, the IdP is Google
Account (accounts.google.com); whereas it is AppleID
(https://appleid.apple.com/) for iOS and Windows Live ID
1More precisely the “Identity Federation Framework” (ID-FF) formulated
by the  Liberty Alliance (LA, in short) consortium.
(www.live.com) for Windows. Among them, Apple ID and
Windows Live ID are mostly used to access services asso-
ciated with Apple and Windows respectively. Only Google
provides a Federated Login service based on the OpenID and
OAuth protocols to allow users to use their Google accounts
to access services outside the Google identity domain .
Even though it adds an element of portability, the Google
IdP acts just like any third party IdP holding user attributes
and so cannot be tagged as a Personal IdP.
III. PORTABLE PERSONAL IDENTITY PROVIDER
At ﬁrst we deﬁne the term Portable Personal Identity
Provider and then we utilise this term to deﬁne the concept
of Personal Identity Federation.
Deﬁnition: Portable Personal Identity Provider (PPIdP) -
A type of Identity Provider that is under the full control of
a user and resides in a mobile device owned and/or used by
the user can be deﬁned as the Personal Identity Provider. It
is the user who must decide what attributes should be stored
in such an IdP and which attributes should be released to
which SP by this IdP.
Since the user can add/edit/update attributes into this IdP,
the IdP must provide an interface to do so as well as an
interface to set any attribute release policies. It is also the
responsibility of the IdP to ensure that all user attributes are
stored safely and securely. In addition, such an IdP adds
the feature of portability which allows the user to use it
while on the move. In the context of this paper, our focus
is mainly on the mobile phone, however, the concept can
easily be adapted to other mobile devices as well. Windows
CardSpace, a former initiative from Microsoft, could act as a
type of personal IdP  along with other functionalities and
was included with several versions of Windows operating
system such as Windows 7 and Windows Vista. However,
it was not portable since it was only available for desktops.
Currently there is no such personal yet portable IdP and our
implementation described here aims to ﬁll in this gap.
Deﬁnition: Personal Identity Federation - When an Identity
Federation is created using a PPIdP, it can be deﬁned as the
Personal Identity Federation.
In a way, this is an extension of the traditional Identity
Federation and also can be of two types: Type 1 & Type
With the advent of Identity 2.0, User-centric Identity
Management has gained considerable attention. There is no
formal deﬁnition for the term User-centric Identity Manage-
ment, however, it is believed to mean an IMS which allows
users to have considerable control over their attributes so
that users can choose which attributes they want to release
to a SP . Windows CardSpace and OpenID are examples
of the User-centric IMS. However, before the attributes
can be released, users must register to the respective IdP
and provide those attributes which are then stored in the
IdP. With some recent incidents in which sensitive user
data (read attributes) were stolen from some major global
companies (which also acts as, more or less, SILO IdPs
for their respective services ) such as Sony (77 millions
of user accounts were affected ), LinkedIn (more than
six million passwords had been stolen ), Apple (over 1
million Apple IDs fell into the wrong hand), users are
rightfully worried to store crucial user data into these IdPs.
Moreover, in many IMS, a legal contract between the IdP
and the SP dictates the handling of user attributes between
themselves. However, there may not be any legal contract
between the user and the IdP and therefore the handling
of attributes may be governed by the respective Terms
& Conditions (T&C). The absence of any legal contract
between the user and the IdP means that the handling of
user attributes is only bound by a trust assumption where
the user can only hope that the respective party will honour
the imposed trust .
Furthermore, when there are many more IdPs, users will
feel overloaded to manage attributes spread over these IdPs
and also the same attributes will be stored in multiple places
resulting in unnecessary redundancy and thus increasing
the chance of theft. All these problems can be tackled
signiﬁcantly by harnessing the true potential of the User-
centric IdM by letting users not only choose which attributes
to release but also to store them in fewer IdPs which are
preferably under their own control. A personal IdP is an
excellent choice for this since it allows the user to manage
all crucial attributes from a central place. We understand
that sometimes it is required by the SP to have higher
assurances about user attributes when the user tries to access
sensitive services such as Governmental or Health Services.
In such scenarios, the SP would only trust attributes released
by a highly trusted IdP. The number of such sensitive
online services will be essentially low compared to the
number of general non-sensitive services. This means that
the number of highly trusted IdPs will be much lower than
the number of general IdPs since there is a signiﬁcantly
higher administrative cost associated with establishing and
maintaining a highly trusted IdP. In fact, not all IdPs need to
be a highly trusted IdP. In most of these general IdPs, user
attributes are mostly provided by the users themselves. Our
main focus is to get rid of all these general IdPs and replace
them with the PPIdP. This will allow users to maintain a
lower number of highly trusted IdPs that could be used
to access only those services that ask for attributes to be
released from a highly trusted IdP and a single PPIdP which
could be used for the rest of other general services.
In addition, such an IdP has added advantages. The
traditional IdPs cannot produce many dynamic attributes
such as the current location data of the user. We can use
the PPIdP to create dynamic attributes whenever required
and provide them to SP during any service access scenario.
B. Key Issues
Designing and developing a PPIdP requires several key
issues to be addressed which are discussed below:
•Technical Challenges: The existing APIs of different
IdM protocols (e.g. SAML and OpenID) have not been
developed with any locally hosted IdP in mind. The
general assumption is that both the IdP and the SP
are online and visible to each other. Since our PPIdP
will be essentially hosted inside the mobile device, this
assumption does not hold. In addition, all IdM protocols
are based on standard web technologies, therefore, we
need to ensure that the IdP is compatible with such web
•Trust Issues: Implicit in every Identity Management is
the issue of trust. Hence, we need to closely examine
the trust assumptions and requirements that might arise
while using our IdP.
•Attribute Storage: Every IdP has to store and handle
user attributes. The IdP must provide an interface to
allow the user to provide new attributes and update
existing ones. Also the IdP should ensure that these
attributes are stored safely and securely.
•Attribute Authorisation: In addition, the IdP must pro-
vide an interface to allow the user to set up any At-
tribute Release Policy (ARP). This will ensure several
key requirements of an IMS such as Explicit Consent,
Transparency and Data Control .
IV. PROOF OF CONCEPT
To prove the applicability of our proposed PPIdP, we
have developed a proof of concept prototype. The current
implementation of the prototype is based on SAML and
OpenID protocols. At ﬁrst, we need to choose a platform
from several popular platforms namely Android, iOS, Win-
dows and Blackberry. Since both SAML and OpenID have
a Java API, we have been looking for a platform with
strong support for Java. With this in mind, Android has been
chosen as our development platform. The architecture of the
prototype is given in Figure 2: The prototype consists of two
major components called the Personal Attribute Store (PAS)
and the IdP Component. Both of them are discussed below.
A. Personal Attribute Store
As the name suggests, the Personal Attribute Store is
where all user attributes will be stored and is a necessary
companion of the proposed IdP. It consists of a back-end
database to store the attributes and a user interface for users
to manipulate their attributes. It also has interfaces to com-
municate with internal sensors (such as the GPS receiver)
of mobile phones to collect contextual information and store
them as dynamic attributes. Android is also bundled with
Figure 2. Architecture of the PPIdP Prototype.
support for the SQLite Database  to be used as the back-
end database to store user attributes. To ensure the security of
stored attributes, it is preferred that attributes are encrypted
before storage. We have used an open source library called
SQLCipher  to encrypt attributes before storage and
decrypt during usage. SQLCipher provides fast and secure
256-bit AES encryption of SQLite database ﬁles and that
alleviates us from the manual encryption and decryption of
The PAS has been developed as an Android app. Every
ﬁrst-time user of the PPIdP must create an account by pro-
viding a username and password along with other attributes.
The user must use that identiﬁer (and the credential) to
manipulate attributes and also to start the IdP. Once the user
is logged in, a session is created and she is presented with
the main control panel of PAS which has several options
(Figure 3). The user can choose the Add option to add a
new attribute, Edit and Delete options to edit and delete any
existing attribute(s) respectively, Exit option to exit the AS
and Sign Out option to sign out by deleting the existing
session. If the user exits the AS without signing out, the
session will be kept for an hour. When the user launches
the AS next time and the session has not expired, the user
will be automatically taken to the main control panel of
the PAS. This saves the user to log in every time the AS is
launched. The panel also shows the already added attributes,
if any, at the bottom part of the screen. The functionalities
of other options will be discussed in due course. The user
also needs to generate a secret key that will be used for
encryption/decryption of user attributes into the database.
The secret key is generated as a conﬁguration parameter by
hashing two values that the user needs to provide: the mobile
phone number of the user and a chosen password.
B. Identity Provider Component
The IdP component is responsible for providing IdP
services and also has been developed as an Android app.
The IdP has two sub-components: the IdP Context and the
Figure 3. Main control panel
of the PAS. Figure 4. Main control panel
of the IdP.
Control Panel. The IdP context actually consists of several
servlets. The SAML servlet is responsible for trapping the
SAML requests and then respond to them. The OpenID
context is to handle OpenID requests. To develop the SAML
servlets, at ﬁrst we have considered using the OpenSAML li-
brary . OpenSAML is a set of open source Java and C++
libraries that can be used for SAML development. However,
it has quite a large number of external dependencies (more
than 20 external jar ﬁles) which would increase the size of
the app considerably and many of these jar ﬁles could not be
compiled with the Dalvik VM of the Android platform. To
overcome the problem, we developed a subset of the SAML
protocol based on the Web Browser SSO Proﬁle and HTTP
Post binding. In this way, we have managed to reduce the
size of the app considerably. The OpenID servlet has been
developed using the OpenID4Java Libraries .
The user can use the same username/password pair of
the PAS to log in to the IdP component and to access
the control panel. The control panel provides the option to
Start/Stop the IdP component using the Start/Stop button
respectively (Figure 4). When the Start button is touched,
the IdP component starts running in the background. Then
the user can use their preferred browser of the mobile phone
to access federated services. When an authentication request
arrives at one of the contexts, it can access the same back-
end database mentioned previously to retrieve user attributes
and then can create responses using those attributes. We
have used the simpleSAMLphp  and the JanRain PHP
OpenID libraries  for deploying SAML and OpenID
service providers respectively. At this point, we will discuss
some key challenges we have faced to develop our PPIdP.
1) Web Server: The ﬁrst challenge was to ﬁnd a suitable
web container for the Android platform. After a thorough
search, Jetty Web Server, an open source HTTP Server and
Java Servlet Container , seems to be the only candidate
that met our requirements.
2) Visibility Issues: The second challenge was to solve
the problem of visibility between the IdP and SP. In the
traditional setting, both IdP and SP are online and visible
to each other. In our case, the IdP is installed in the device
as a local web server and therefore is not visible to the
SP. We have solved this problem by embedding an XHTML
runs into the browser, it is possible to contact the respective
IdP context using the localhost URL. This is a standard
technique used in the SAML SSO Browser proﬁle. We have
just adopted the same behaviour and modiﬁed the code
of the simpleSAMLphp and JanRain PHP libraries for our
scenarios. Note that the IdP has no problem contacting the
SP since the SP has be to online to provide online services.
3) SAML Trust Issues & Dynamic Federation: The third
challenge was to handle the fundamental trust issues in-
volved in the SAML. A SAML SP needs to trust that the
IdP will authenticate the user using appropriate security
mechanisms and release attributes to the SP as per the
contractual agreement . Similarly, the IdP has to trust
that the SP will not abuse the released attributes and use
them only for the stated purpose as per the agreement.
Trust in SAML is initiated when the respective IdP and the
SP exchange metadata between themselves. The exchanged
metadata is then stored in a repository which is used to
update the respective Trust Anchor List (TAL) .The SP
and IdP will only trust entities which can be found in the
Metadata must be exchanged before the IdP and the SP
can interact with each other and the exchange takes place
externally during/after the parties bind themselves with a
technical contract. Now exchanging metadata in this way has
two potential problems. Firstly, pre-conﬁguring trust before
any interaction hinders the establishment of a federation
between two prior unknown parties in a dynamic fashion.
Secondly, pre-conﬁguring trust between two organisations
by exchanging metadata is usually carried by the respective
administrators. Now, we are faced with a dilemma with our
case of PPIdP. We do not want to burden users with the task
of metadata exchange and at the same time there must be a
way for SAML-enabled parties to exchange metadata with
each other. We can address both these issues by allowing
users to create federations in a dynamic fashion.
The authors in  presented a mechanism by which a
SAML federation can be created in a dynamic fashion. There
is no administrative overhead associated with the technique
allowing any general user to establish federations whenever
required. We have utilised the same approach for creating a
Dynamic Federation. According to that method, the entity ID
(a unique identiﬁer given to an IdP or a SP) of each SAML
entity (IdPs and SPs) will represent the endpoints from
where their respective metadata can be fetched dynamically.
At ﬁrst, the user will need to generate a temporary code
from the IdP. The SP is assumed to provide an interface
to add the IdP, preferably at the Where Are You From
(WAYF) of the SP. Then the user will input the entity ID
of the IdP into that page along with the code. The SP will
send a request for dynamic federation into that entity ID
along with the respective code and the SP’s entity ID. After
validating the code, the IdP will use the SP’s entity ID to
fetch SP’s metadata and save it to the IdP’s TAL. Then the
IdP will send back its metadata to the SP which will be
ultimately stored into the SP’s TAL. Since the SP might
not trust any dynamically added IdP, any such IdP will be
treated as an untrusted entity to the SP whereas the IdP will
treat the SP as an untrusted entity initially. The SP will be
promoted as a semitrusted entity only when a user releases a
subset of attributes to that SP. The same mechanism can be
used to federate two IdPs by a user of both IdPs and thus
enabling a Type 2 federation. In this case, one of IdPs is
assumed to be fully trusted to the SP by having a formal trust
agreement between them. This will allow the fully trusted
IdP to delegate the authentication task to the dynamically
added IdP. The dynamic IdP will release user attributes to the
trusted IdP which, then, will release them to the SP. To avoid
any privilege escalation, the authors proposed to utilise the
NIST LoA (Level of Assurance or Level of Authentication
) level of 1 to signify that the level of assurance is low
since attributes are from the PPIdP.
C. SAML Protocol Flow
In our work, we have adopted a similar approach, as
discussed above, for creating a dynamic federation. A SAML
IdP and a SAML SP have been deployed using simple-
SAMLphp. Their metadata have been exchanged beforehand
to ensure that are considered fully trusted to each other. Now
to create a Type 1 dynamic federation, the user ﬁrst generates
a temporary code using the user interface of the PAS. Then
the user visits the SP where the user is presented with a form
to allow her to create the dynamic federation. The chosen
entity ID for our IdP is https://localhost:8443/saml/idp. The
user inputs that entity ID along with the code. Then the
previously described mechanism for exchanging metadata
technique as described before to contact with the IdP. At
the end, the respective metadata will be exchanged making
the PPIdP and the SP a part of the Personal Identity
Federation. At this point, the usual SAML Protocol ﬂow
takes place. The user visits the SP to access one of its
resources. The SP forwards the user to the WAYF Page
where she chooses the PPIdP. The SP creates a SAML
authentication request and forwards the request to the PPIdP
using an embedded XHTML form and submitting the form
IdP traps the request and presents a login form to the
user. The user logs in using her username/password. Once
the authentication is successful, a new form with all user
attributes are presented and the user selects the attributes
that she wants to release to the SP. A SAML assertion using
the selected attributes is created and returned to the SP. The
SP retrieves the user attributes and makes an authorisation
decision to allow or reject the user to access the resources
(Figure 5). The PAS also allows the option to create a
pre-conﬁgured Attribute Release Policy for any speciﬁc SP
using the Set/Reset/View/Edit Authorisation option of the
PAS main control panel (Figure 3). The IdP will use the
ARP to ﬁlter out any attributes before the attribute selection
Since the PPIdP has been dynamically added to the SP,
the SP must treat it as an untrusted entity even if the IdP
acts honestly. In this way, the SAML implementation of the
IdP will essentially act equivalently to the OpenID. Thus
this technique will be suitable for general SPs which do not
require users attributes coming from a highly trusted IdP. In-
terestingly, some attributes (such as credit card information)
are self-certiﬁable. It does not matter if they are coming from
a highly trusted IdP or an untrusted IdP since the SP can
verify the authenticity of those attributes and can use them
to allow users to access sensitive services. In such scenarios,
the PPIdP would be truly beneﬁcial.
Figure 5. Released attributes
in Type 1 Federation. Figure 6. Two authentication
sources at the trusted IdP.
We have deployed another scenario in which the PPIdP can
be federated with a trusted IdP to create a Type 2 federation
using the similar approach. Here, the fully trusted IdP would
act like a Proxy IdP as described in  and would delegate
the authentication service to the PPIdP which is hidden from
the SP. The PPIdP will essentially act as an authentication
source for the trusted IdP (Figure 6). The protocol ﬂow
will be something like this: the user visits the SP to access
one of its resources. The user is forwarded to the WAYF
page where the user selects the trusted IdP. A SAML
authentication request is sent to the trusted IdP where the
user is presented with a selection of authentication sources:
The PPIdP (Mobile IdP in Figure 6) or the trusted IdP itself
(example-sql in Figure 6). Assuming the user selects the
PPIdP, a SAML authentication request is forwarded to the
PPIdP and the usual protocol ﬂow takes place. At the end, a
SAML assertion with the selected attributes is sent back to
the trusted IdP. The trusted IdP retrieves the attributes and
creates a SAML assertion with those attributes. To reﬂect
the fact that these attributes have come from the PPIdP, it
also inserts a LoA value of 1 for this assertion. The assertion
is sent back to the SP. Then the SP will determine which
resources the user can access using the released attributes
having a LoA value of 1 (Figure 7). In case, if the user would
have chosen the trusted IdP, the assertion would contain
a LoA value of 2 and might allow users to access more
restricted services (Figure 8).
Figure 7. LoA 1 for attributes
from PPIdP. Figure 8. LoA 2 for attributes
from trusted IdP.
D. OpenID Protocol Flow
Compared to the SAML, OpenID is a simple protocol.
There is no complex trust assumptions to consider as every
OpenID provider is considered trusted. There is no need
to create any federation using complex metadata exchange
procedure in OpenID. A protocol ﬂow for OpenID using our
PPIdP is as follows.
When the user visits the SP (Relying Party or RP
in OpenID terminology) to access one of their ser-
vices, the user visits the RP where the user has op-
tion to enter her OpenID. The user enters her OpenID
(https://localhost:8443/OpenIDTest) and touches the verify
button. The IdP is discovered using the mechanism described
discovered, we have opted out the optional key exchange
step of the OpenID. Then the SP creates an authentication
request which is submitted to the PPIdP using the same
approach. The PPIdP traps the request and forwards it to
the appropriate servlet. The user is presented with a Login
form where the user submits her username/password. Then
a response is generated and returned to the RP. The RP then
sends a signature veriﬁcation request to the PPIdP where the
signature is veriﬁed as per the OpenID speciﬁcation. Then a
veriﬁcation response is generated and is sent back to the RP.
At this point the user is considered as authenticated and the
RP takes an authorisation decision to allow/reject the user’s
request to access the service.
V. SECURITY & PRIVACY ANALYSIS
A. Security Analysis
Since the PPIdP has been fully developed based on the
standardised SAML and OpenID protocols, the security in
communication will not be lower than the security of the
respective protocol. However, the nature of the deployment
introduces several novel security requirements:
Name-Qualifying/Impersonation Issues: The most dif-
ﬁcult problem in terms of security for implementing the
PPIdP is how to name-qualify different PPIdPs installed
in different phones. In general settings of SAML and
OpenID, the entity ID of the IdP and the OpenID are name-
qualiﬁed based on the Domain Naming System (DNS).
This ensures that no two IdPs have the same entity IDs
meaning that transient identiﬁers of the users will be dif-
ferent even though two users of two different IdPs might
have similar local identiﬁers in SAML or no two users
have same OpenIDs in OpenID. Since PPIdPs installed
in different phones will have essentially the same entity
ID (https://localhost:8443/saml/idp) or the same OpenID
IdP name (https://localhost:8443/OpenIDTest) and different
users in different phones might have the same username,
malicious users might use this techniques to impersonate
users from other phones. The problem can be solved by
devising a mechanism to name-qualify each IdP installed
in different phones from the viewpoint of each SP. We
have developed a Request/Response mechanism to solve the
problem. The mechanism is described below for the SAML
Type 1 federation:
1) When the user provides the entity ID
(https://localhost:8443/saml/idp) of PPIdP and
the respective code while creating the Dynamic
Federation, the SP generates a random hash
and a password. The random hash is to be
included in the provided entity ID so that it looks
The modiﬁed entity ID and the password are also
exchanged during the metadata exchange period. The
metadata of the PPIdP is based on the modiﬁed entity
ID which will be used for any subsequent SAML
protocol ﬂow. Once the metadata is successfully
exchanged and a dynamic federation is created, both
the PPIdP and the SP store four pieces of information:
the modiﬁed entity ID, the password, the entity ID of
the SP and the code used for dynamic federation.
2) When the user wishes to access one of the restricted
resources, just before the WAYF Page is shown to the
user, the SP sends a message to the IdP providing
the entity ID of the SP and the code and ask for the
PPIdP’s entity ID and corresponding password.
3) The PPIdP retrieves the saved entity ID along with the
password using the SP’s entity ID and the provided
code and send them to the SP.
4) The SP matches the supplied entity ID and the pass-
word with its database entry. Then the supplied entity
ID is used to ﬁlter out other PPIdP entity IDs (e.g.
entity IDs that belong to the https://localhost:8443/
domain) when the TAL is presented. Note that other
entity IDs beloning to other trusted or untrusted IdPs
are not ﬁltered out.
5) When the user chooses one of the IdPs, the usual
SAML protocol ﬂow resumes.
This mutual authentication between the IdP and SP serves
two purposes: i) it helps the SP to name-qualify each PPIdP
and ii) a malicious user will not be able to impersonate other
users of different phones.
A SP has, more or less, very little to gain by acting
maliciously since a malicious act by the SP will expose its
services to unauthorised users. However, a malicious PPIdP
has lots to gain if it can impersonate another PPIdP. Using
this protocol, a malicious PPIdP would require to know both
the modiﬁed entity ID and the respective password. Since
all communications take place in encrypted channels using
HTTPS, the only option for a malicious PPIdP is to guess
both the modiﬁed entity ID and the password. As both the
hash of the entity ID and the password consist of 12 digits
of randomly generated alphanumeric characters, they will
be difﬁcult to guess. The similar technique has been used
to create a SAML Type 2 federation and an OpenID Type
1 federation using the PPIdP.
The whole mechanism is invisible to the user which allevi-
ates them from any associated complexities. Interested users,
however, have the option to view the modiﬁed entity ID
and OpenID provided by each respective SP using the View
EntityID/OpenID option of the PAS control panel (Figure 3).
In cases where the user is accessing the federated SP from
other devices than her mobile phone and thus has no access
to the PPIdP, our intermediate request/response mechanism
will time out and the user cannot view any dynamically
added PPIdPs. The presented TAL will contain only the
trusted/untrusted list of IdPs. The proposed mechanism has
been tested with three different PPIdPs installed in three
different Android phones and the result was ﬂawless.
Data Theft: As all user attributes are stored centrally in
a database, we had to take great care to ensure that user
attributes are stored safely and securely. This is ensured
with the help of the SQLCipher library which encrypts every
single attributes stored in the database. The database is saved
in the external storage of the android phone to allow that
both PAS and PPIdP can be access the database. Because
of the use of the SQLCipher Library with a secret key (as
described in Section IV-A) that only the PAS and PPIdP
know,the whole database will be inaccessible by other apps.
This undermines any threats involved in cases other apps try
to access the database or even if the database gets stolen.
The security of the system can be increased furthermore
by storing attributes in a hardware/software based TPM.
However, the availability of such TPMs for the Android
platform is still rare. Therefore it will take sometimes for any
wide-spread adoption of this mechanism. Another alternative
approach could be the usage of smartcards in which user
attributes will be stored in smartcards in an encrypted
Intentional/Accidental Corruption of the Database:
Since the database acts as the central repository, it is
essential to guard against any intentional/accidental cor-
ruption of the database. To ensure redundancy, a backup
database is always maintained in the internal storage of
the PPIdP and PAS which are private to the applications
and are inaccessible by other applications, attackers or even
to the user. The data in the backup database are stored in
ecnrypted format just like the main database. Every single
operation (addition/updating of attributes) is synced across
both databases. In case the main database gets corrupted,
the PAS provides the option to allow the user to restore user
attributes from the backup database using the Restore Data
option of the PAS control panel (Figure 3). Furthermore,
users also can create a secondary backup of database to
allow them to copy the respective database into some other
places (e.g. PC, Laptop, etc.) using the Backup Data option
of the PAS control panel (Figure 3) and then restore again
B. Privacy Analysis
The core privacy requirements for any Identity Manage-
ment System is to ensure that it supports pseudonymity and
empowers uses by transparency and by giving full control
over their own data . The support of pseudonymity
will enable users to provide pseudonymous identiﬁers to
the SP which will ensure that different SPs cannot collude
together to generate a comprehensive proﬁle of the user.
The SAML supports pseudonymity with the concept of the
transient identiﬁer. The PPIdP adopts the same technique
that generates a different transient identiﬁers for different
SPs. This enables each SP to maintain a session with a
speciﬁc user, however undermines any possibility of linking
the same user across different SPs.
The PPIdP uses two techniques to empower users. Firstly,
the PAS allows to set a general ARP that will dictate which
attributes to release to all SPs. Users also can set a policy for
each single SP. Secondly, the user is presented with a form
containing the attributes (excluding the attributes that have
been ﬁltered out based on the ARP) just before the attributes
are about to be released. This allows the user again to ﬁne-
tune the number of attributes the user wants to release to
that SP. Moreover, the PAS also provides an interface that
the user can use to examine the history of which attributes
have been released to which entities by using the Released
Attributes option of the PAS control panel (Figure 3). All
these features enable the PPIdP to meet the Explicit Consent,
Transparency and Data Control requirements of an IMS.
Our approach offers many key advantages. Here we
outline just a few:
•As stated before, this approach empowers users to have
full control over the IdP and the attributes stored. Users
control which attributes to be released and to which SP.
•The PAS acts as the central repository to store crucial
user attributes. Since the attributes are not scattered
over many IdPs, their management become easier.
•Users can create Type 1 or 2 federations just in time
and whenever required.
•Usually attributes stored in traditional IdPs are static
in nature. Mobile phones can be used to generate
dynamic attributes such as spatial values that can be
used to provide context aware services in a secure
way using standard SAML protocol. Such dynamic
attributes can also be used to deploy context aware
•Leaking crucial attributes from mobile phones is an
important issue. Once an App is granted with a per-
mission to access any attributes or resources, the user
cannot control when and for how long that app can
access those resources. Storing all attributes in the
PAS and binding them under an advanced authorisation
framework such as XACML  coupled with a SAML
IdP (like ours), ﬁne-grained access control mechanisms
can be provided.
•By accommodating other IdM protocols, the PPIdP can
provide a single interface to interact with all types of
Unfortunately, our approach also has some limitations:
•It currently supports SAML Web Browser SSO Proﬁle
and HTTP Post binding and so is incompatible with
other SAML proﬁles and bindings.
•Currently our IdP does not support any other advanced
OpenID extensions such Provider Authentication Policy
Extension (PAPE)  and OpenID Attribute Exchange
•The PAS provides a primitive way of setting authorisa-
tion. There is no policy based approach to dictate how
attributes should be released.
C. Future Work
To harness the full potential of our approach, there are
several directions to take from here:
•We plan to add support for other SAML proﬁles and
bindings which would allow our PPIdP to act as a
comprehensive SAML IdP.
•We plan to add the functionalities of OpenID PAPE and
Attribute Exchange into the OpenID Context.
•Other IdM protocols especially the very popular OAuth
(oauth.net) could be added to our PPIdP.
•If a user has more than one phones, the current im-
plementation of the PPIdP provides no easier way to
share attributes among different devices. It will require
the user to create a backup of the database and copy
it manually to other phones which could be a complex
task. A better approach will be to use cloud services to
sync data automatically across devices.
•Adding capabilities to allow the PAS to gather con-
textual information from external sensors (which are
not inside a mobile phone and are installed on the
surrounding environments) via network interfaces such
as Near Field Communication (NFC), Bluetooth, etc.
or using the mobile phone’s camera.
•A good research questions would be to ﬁnd a way for
attributes from different sources to be aggregated and
stored in the PAS.
In this paper, we have presented a detailed analysis on
several aspects of Portable Personal Identity Provider in
Mobile phones. We have explained the motivation behind
our work, deﬁned several novel concepts, discussed the key
challenges to implement those concepts and ﬁnally described
our implemented proof of concept. As the online services
proliferate, it will be increasingly difﬁcult for people to
manage their attributes which are currently scattered over
many places. A portable personal IdP in mobile phones can
be a great tool in aiding users to manage their attributes
and will allow users to get back the control over their own
attributes which is missing in the current setting. We strongly
believe that our approach has great potential and can have
a far reaching impact in a world of mobile devices.
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