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Framework for a DLT Based COVID-19 Passport


Abstract and Figures

Uniquely identifying individuals across the various networks they interact with on a daily basis remains a challenge for the digital world that we live in, and therefore the development of secure and efficient privacy preserving identity mechanisms has become an important field of research. In addition, the popularity of decentralised decision making networks such as Bitcoin has seen a huge interest in making use of distributed ledger technology to store and securely disseminate end user identity credentials. In this paper we describe a mechanism that allows one to store the COVID-19 vaccination details of individuals on a publicly readable, decentralised, immutable blockchain, and makes use of a two-factor authentication system that employs biometric cryptographic hashing techniques to generate a unique identifier for each user. Our main contribution is the employment of a provably secure input-hiding, locality-sensitive hashing algorithm over an iris extraction technique, that can be used to authenticate users and anonymously locate vaccination records on the blockchain, without leaking any personally identifiable information to the blockchain. KeywordsLocality-sensitive hashBiometric hashBlockchainVaccination passport
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Framework for a DLT Based COVID-19 Passport
Sarang Chaudhari, Michael Clear, Philip Bradish, and Hitesh Tewari
Indian Institute of Technology, Delhi, Trinity College Dublin, Ireland
Abstract. Uniquely identifying individuals across the various networks
they interact with on a daily basis remains a challenge for the digital
world that we live in, and therefore the development of secure and effi-
cient privacy preserving identity mechanisms has become an important
field of research. In addition, the popularity of decentralised decision
making networks such as Bitcoin has seen a huge interest in making use
of distributed ledger technology to store and securely disseminate end
user identity credentials. In this paper we describe a mechanism that
allows one to store the COVID-19 vaccination details of individuals on
a publicly readable, decentralised, immutable blockchain, and makes use
of a two-factor authentication system that employs biometric crypto-
graphic hashing techniques to generate a unique identifier for each user.
Our main contribution is the employment of a provably secure input-
hiding, locality-sensitive hashing algorithm over an iris extraction tech-
nique, that can be used to authenticate users and anonymously locate
vaccination records on the blockchain, without leaking any personally
identifiable information to the blockchain.
1 Introduction
Immunization is one of modern medicine’s greatest success stories. It is one of the
most cost-effective public health interventions to date, averting an estimated 2 to
3 million deaths every year. An additional 1.5 million deaths could be prevented
if global vaccination coverage improves [13]. The current COVID-19 pandemic
which has resulted in millions of infections worldwide [3] has brought into sharp
focus the urgent need for a “passport” like instrument, which can be used to
easily identify a user’s vaccination record, travel history etc., as they traverse the
globe. However, such instruments have the potential to discriminate or create
bias against citizens [10] if they are not designed with the aim of protecting
the user’s identity and/or any personal information stored about them on the
Given the large number of potential users of such a system and the involve-
ment of many organizations in different jurisdictions, we need to design a system
that is easy to sign up to for end users, and for it to be rolled out at a rapid rate.
The use of hardware devices such as smart cards or mobile phones for storing
such data is going to be financially prohibitive for many users, especially those
This publication has emanated from research conducted with the financial support
of Science Foundation Ireland under Grant Number 13/RC/2094 (Lero).
arXiv:2008.01120v7 [cs.CR] 18 Jan 2021
2 Sarang Chaudhari, Michael Clear, Philip Bradish, and Hitesh Tewari
in developing countries. Past experience has shown that such “hardware tokens”
are sometimes prone to design flaws that only come to light once a large number
of them are in circulation. Such flaws usually require remedial action in terms
of software or hardware updates, which can prove to be very disruptive.
An alternative to the above dilemma is an online passport mechanism. An
obvious choice for the implementation of such a system is a blockchain, that
provides a “decentralized immutable ledger” which can be configured in a man-
ner such that it can be only written to by authorised entities (i.e. there is no
requirement for a hard computation such as proof-of-work (PoW) to be carried
out for monetary reward), but can be queried by anyone. However, one of the
main concerns for such a system is based on: How does one preserve the privacy
of user’s data on a public blockchain while providing a robust mechanism to
link users to their data records securely? In other words, one of the key require-
ments is to avoid having any personally identifiable information (PII) belonging
to users stored on the blockchain.
In the subsequent sections we describe some of the key components of our
system and the motivation that led us to use them. The three major compo-
nents are - extraction of iris templates, a hashing mechanism to store them
securely and a blockchain technology. Finally, we present a formal description
of our framework which uses the aforementioned components as building blocks.
However, first we will briefly discuss some related work and then briefly some
preliminaries with definitions and notation that are used in the paper.
1.1 Related Work
There has been considerable work on biometric cryptosystems and cancellable
biometrics, which aims to protect biometric data when stored for the purpose of
authentication cf. [11]. Biometric hashing is one such approach that can achieve
the desired property of irreversibility, albeit without salting it does not achieve
unlinkability. Research in biometric hashing for generating the same hash for
different biometric templates from the same user is at an infant stage and existing
work does not provide strong security assurances. Locality-sensitive hashing is
the approach we explore in this paper, which has been applied to biometrics in
existing work; for example a recent paper by Dang et al. [4] applies a variant of
SimHash, a hash function we use in this paper, to face templates. However the
technique of applying locality-sensitive hashing to a biometric template has not
been employed, to the best of our knowledge, in a system such as ours.
2 Preliminaries
2.1 Notation
A quantity is said to be negligible with respect to some parameter λ, written
negl(λ), if it is asymptotically bounded from above by the reciprocal of all poly-
nomials in λ.
Framework for a DLT Based COVID-19 Passport 3
For a probability distribution D, we denote by x$Dthe fact that xis
sampled according to D. We overload the notation for a set Si.e. y$Sdenotes
that yis sampled uniformly from S. Let D0and D1be distributions. We denote
by D0
CD1and the D0
SD1the facts that D0and D1are computationally
indistinguishable and statistically indistinguishable respectively.
We use the notation [k] for an integer kto denote the set {1, . . . , k}.
Vectors are written in lowercase boldface letters.
The abbreviation PPT stands for probabilistic polynomial time.
2.2 Entropy
The entropy of a random variable is the average “information” conveyed by the
variable’s possible outcomes. A formal definition is as follows.
Definition 1. The entropy H(X)of a discrete random variable Xwhich takes
on the values x1, . . . , xnwith respective probabilities PrhX=x1i,...,PrhX=
xniis defined as
H(X) :=
PrhX=xiilog PrhX=xii
In this paper, the logarithm is taken to be base 2, and therefore we measure the
amount of entropy in bits.
3 Iris Template Extraction
Iris biometrics is considered one of the most reliable techniques for implementing
identification systems. For the ID of our system (discussed in the overview of
our framework in Section 6), we needed an algorithm that can provide us with
consistent iris templates, which will have not only low intra-class variability,
but also show high inter-class variability. This requirement is essential because
we would expect the iris templates for the same subject to be similar, as this
would then be hashed using the technique described in the section 4. Iris based
biometric techniques have received some good attention in the last decade. One
of the most successful technique was put forward by John Daugman [5], but
most of the current best-in-class techniques are patented and hence unavailable
for an open-source use. For the purpose of writing this paper, we have used the
work of Libor Masek [7] which is an open-source implementation of a reasonably
reliable iris recognition technique. Users can always opt for other commercial
biometric solutions when trying to deploy our work independently.
Masek’s technique works on grey-scale eye images, which are processed in
order to extract the binary template. First the segmentation algorithm, based
on a Hough Transform is used to localise the iris and pupil regions and also isolate
the eyelid, eyelash and reflections as shown in Figures 1a and 1b. The segmented
4 Sarang Chaudhari, Michael Clear, Philip Bradish, and Hitesh Tewari
(a) (b)
Fig. 1: Masek’s Iris Template Extraction Algorithm
iris region is then normalised i.e, unwrapped into a rectangular block of constant
polar dimensions as shown in Figure 1c. The iris features are extracted from
the normalised image by one-dimensional Log-Gabor filters to produce a bit-
wise iris template and mask as shown in Figure 1d. We denote the complete
algorithm by Iris.ExtractFeatureVector which takes a scanned image as input and
outputs a binary feature vector fv ∈ {0,1}n(this algorithm is called upon by
our framework in Section 6). This data is then used for matching, where the
Hamming distance is used as the matching metric. We have used CASIA-Iris-
Interval database [2] in Figure 1 and for some preliminary testing.
Table 1 shows the performance of Masek’s technique as reported by him
in his original thesis [8]. This algorithm performs quite well for a threshold of
0.4 where the false acceptance rate (FAR) is 0.005 and the false rejection rate
(FRR) is 0. These values are used when we present our results to compare the
performance of our technique when a biometric template is first hashed and then
the hamming distance is measured to calculate the FAR and FRR, as opposed to
directly measuring the hamming distances in the original biometric templates.
One would assume the performance of our work to get better with the increase
in efficiency of extracting consistent biometric templates by other methods.
As aforementioned, we rely on the open-source MATLAB code by Libor
Masek. For each input image, the algorithm produces a binary template which
Framework for a DLT Based COVID-19 Passport 5
Threshold FAR FRR
0.20 0.000 74.046
0.25 0.000 45.802
0.30 0.000 25.191
0.35 0.000 4.580
0.40 0.005 0.000
0.45 7.599 0.000
0.50 99.499 0.000
Table 1: FAR and FRR for the CASIA-a Data Set
contains the iris information, and a corresponding noise mask which corresponds
to corrupt areas within the iris pattern, and marks bits in the template as cor-
rupt. These extracted iris templates and their corresponding masks are 20 ×480
binary matrices each. In the original work, only those bits in the iris pattern
that correspond to ‘0’ bits in the noise masks of both iris patterns were used
in the calculation of Hamming distance. A combined mask is then calculated
and both the templates are masked with it. Finally, the algorithm calculates the
bitwise XOR i.e. distance between the masked templates. The steps given below
provides an overview for the algorithm used by Libor:
(template1, mask1) = createiristemplate(image1)
(template2, mask2) = createiristemplate(image2)
c mask =mask1mask2
masked template1=template1(¬c mask)
masked template2=template2(¬c mask)
distance =masked template1masked template2
There are two major issues that we need to deal with before being able to
use these templates in our system, specifically, template masking and conversion
to linear vector.
3.1 Template Masking
The above matching technique requires one to have 2 pairs of iris patterns and
their corresponding masks to calculate the Hamming distance. However for the
application we are targeting, at any time during verification, the system would
have to match the extracted template of an individual (i.e. template and mask)
against a hashed template stored on the blockchain. This means that we cannot
6 Sarang Chaudhari, Michael Clear, Philip Bradish, and Hitesh Tewari
incorporate the above matching algorithm into our system. We have two choices
to mitigate this problem and obtain the masked template for the remaining
1. We can calculate the masked template independently for each sample i.e.
masked template =template (¬mask)
An underlying assumption for this method is that the masks for an individual
would be approximately the same in every sample. This assumption is not
too far-fetched as was clear from the preliminary analysis of our database.
We will refer to these as type1templates.
2. We can maintain a global mask which can be the defined as
global mask =mask1. . . maskl
for all extracted maskiof all imageibelonging to the training database. And
at the time of verification, we generate the masked template as
masked template =template (¬global mask)
This method has some added difficulty in finding the global mask and it also
discards more data from the iris patterns as opposed to directly using the re-
spective maskifor each templatei. But it helps in maintaining a consistency
among the masked templates. We will refer to these as type2templates.
In a follow-up to this paper, we will use and provide results for templates of
both types based on experiments we are conducting at the time of writing.
3.2 Conversion to Linear Vector
For our use case, we need a one-dimensional input stream which can be fed into
the hashing algorithm discussed in the subsequent sections. For converting those
masked template matrices into linear feature vectors, we have two naive choices
of concatenating either the row vectors or the column vectors. Before deciding
the type of conversion, let us look at an important key factor, which is rotational
inconsistencies in the iris templates.
Rotational inconsistencies are introduced due to rotations of the camera, head
tilts and rotations of the eye within the eye socket. The normalisation process
does not compensate these. In order to account for rotational inconsistencies,
when the Hamming distance of two templates is calculated, one template is
shifted left and right bit-wise, and a number of Hamming distance values are
calculated from successive shifts. This bit-wise shifting in the horizontal direction
corresponds to the rotation of the original iris region. This method was suggested
by Daugman [5], and corrects misalignment in the normalised iris pattern caused
by rotational differences during imaging. From the calculated Hamming distance
values, only the lowest is taken, since this corresponds to the best match between
two templates. Due to this, column-wise conversion seems like the most logical
choice as this would allow us to easily rotate the binary linear feature vectors.
Shifting the linear vector by 20 bits will correspond to shifting the iris template
once (recall that the dimension of iris templates is 20 ×480).
Framework for a DLT Based COVID-19 Passport 7
3.3 Wrap-up
Putting it all together, we define the steps of our algorithm Iris.ExtractFeatureVector
that we call upon later.
– Iris.ExtractFeatureVector(image):
(template, mask) = createiristemplate(image) where createiristemplate
is Masek’s open source algorithm.
Obtain masked template (either type1or type2as defined in Section 3.1).
Convert masked template to linear vector as in Section 3.2.
Output binary linear vector fv ∈ {0,1}n
Note that the parameter nis a global system parameter measuring the length
of the binary feature vectors outputted by Iris.ExtractFeatureVector.
4 Locality-sensitive Hashing
To preserve the privacy of individuals on the blockchain, the biometric data has
to be encrypted before being written to the ledger. Hashing is a good alter-
native to achieve this, but techniques such as SHA-256 and SHA-3 cannot be
used, since the biometric templates that we extracted above can show differences
across various scans for the same individual. Hence using those hash functions
would produce completely different hashes. Therefore, we seek a hash function
that generates “similar” hashes for similar biometric templates. This prompts
us to explore Locality-Sensitive Hashing (LSH), which has exactly this property.
Various LSH techniques have been researched to identify whether files (i.e. byte
streams) are similar based on their hashes. TLSH is a well-known LSH function
that exhibits high performance and matching accuracy but, does not provide a
sufficient degree of security for our application. Below we assess another type of
LSH function, which does not have the same runtime performance as TLSH, but
as we shall see, exhibits provable security for our application and therefore is a
good choice for adoption in our framework.
4.1 Input Hiding
In the cryptographic definition of one-way functions, it is required that it is hard
to find any preimage of the function. However, we can relax our requirements for
many applications because it does not matter if for example a random preimage
can be computed as long as it is hard to learn information about the specific
preimage that was used to compute the hash. In this section, we introduce a
property that captures this idea, a notion we call input hiding.
Input hiding means that if we choose some preimage xand give the hash
h=H(x) to an adversary, it is either computationally hard or information-
theoretically impossible for the adversary to learn xor any partial information
about x. This is captured in the following formal definition.
8 Sarang Chaudhari, Michael Clear, Philip Bradish, and Hitesh Tewari
Definition 2. A hash function family Hwith domain X:= {0,1}nand range
Y:= {0,1}mis said to be input hiding if for all randomly chosen hash functions
H$H, all i[n], all randomly chosen inputs x$Xand all PPT adversaries
Ait holds that
Prhxi= 0 ∧ A(i, H(x)) 1i
Prhxi= 1 ∧ A(i, H(x)) 1i
where λis the security parameter.
4.2 Our Variant of SimHash
Random projection hashing, proposed by Charikar [1], preserves the cosine dis-
tance between two vectors in the output of the hash, such that two hashes are
probabilistically similar depending on the cosine distance between the two preim-
age vectors. This hash function is called SimHash. We describe a slight variant
of SimHash here, which we call S3Hash. In our variant, the random vectors that
are used are sampled from the finite field of F3={−1,0,1}. Suppose we choose
a hash length of mbits. Now for our purposes, the input vectors to the hash
are binary vectors in {0,1}nfor some n. First we choose mrandom vectors
ri${−1,0,1}nfor i∈ {1, . . . , m}. Let R={ri}i∈{1,...,m}be the set of these
random vectors. The hash function S3HashR:{0,1}n→ {0,1}mis thus defined
S3HashR(x) = (sgn(hx,r1i),...,sgn(hx,rmi)) (1)
where sgn :Z→ {0,1}returns 0 if its integer argument is negative and returns
1 otherwise. Note that the notation ,·i denotes the inner product between the
two specified vectors. Let x1,x2∈ {0,1}nbe two input vectors. It holds for all
i∈ {1, . . . , m}that Pr[h(1)
i] = 1 θ(x1,x2)
πwhere h(1) =S3HashR(x1),
h(2) =S3HashR(x2) and θ(x1,x2) is the angle between x1and x2. Therefore the
similarity of the inputs is preserved in the similarity of the hashes.
An important question is: Is this hash function suitable for our application?
The answer is in the affirmative because it can be proved that the function
information-theoretically obeys a property we call input-hiding that we defined
in Section 4.1. We recall that this property means that if we choose some binary
vector x∈ {0,1}nand give the hash h=S3HashR(x) to an adversary, it is either
computationally hard or information-theoretically impossible for the adversary
to learn xor any partial information about x. This property is sufficient in our
application since we only have to ensure that no information is leaked about
the user’s iris template. We now prove that our variant locality-sensitive hash
function S3Hash is information-theoretically input hiding.
Theorem 1. Let Xdenote the random variable corresponding to the domain of
the hash function. If H(X)m+λthen S3Hash is information-theoretically
input hiding where λis the security parameter and H(X)is the entropy of X.
Framework for a DLT Based COVID-19 Passport 9
Proof. The random vectors in Rcan be thought of as vectors of coefficients
corresponding to a set of mlinear equation in nunknowns on the left hand side
and on the right hand side we have the melements, one for each equation, which
are components of the hash i.e. (h1, . . . , hm). Now the inner product is evaluated
over the integers and the sgn function maps an integer to an element of {0,1}
depending on its sign. The random vectors are chosen to be ternary. Suppose
we choose a finite field Fpwhere p2(m+ 1) is a prime. Since there will be no
overflow when evaluating the inner product in this field, a solution in this field is
also a solution over the integers. We are interested only in the binary solutions.
Because m < n, the system is underdetermined. Since there are nmdegrees
of freedom in a solution, it follows that there are 2nmbinary solutions and
each one is equally likely. Now let rdenote the redundancy of the input space
i.e. r=nH(X). The fraction of the 2nmsolutions that are valid inputs
is 2nmr. If 2nmr>2λ, then the probability of an adversary choosing the
“correct” preimage is negligible in the security parameter λ. For this condition
to hold, it is required that nmr > λ (recall that r=nH(X)), which
follows if H(X)m+λas hypothesized in the statement of the theorem. It
follows that information-theoretically an unbounded adversary has a negligible
advantage in the input hiding definition.
Our initial estimates suggest that the entropy of the distribution of binary
feature vectors outputted by Iris.ExtractFeatureVector is greater than m+λfor
parameter choices such as m= 256 and λ= 128. A more thorough analysis
however is deferred to future work.
4.3 Evaluation
We have ran experiments with S3Hash applied to feature vectors obtained using
our Iris.ExtractFeatureVector algorithm. The distance measure we use is the ham-
ming distance. The results of these experiments are shown in Table 2. Results
for a threshold of 0.3 in particular indicates that our approach shows promise.
We hope to make further improvements in future work.
5 Blockchain
A blockchain is used in the system for immutable storage of individuals’ vaccina-
tion records. The blockchain we employ is a permissioned ledger to which blocks
can only be added by authorized entities or persons such as hospitals, primary
health care centers, clinicians etc. Such entities have to obtain a public-key cer-
tificate from a trusted third party and store it on the blockchain as a transaction
before they are allowed to add blocks to the ledger. The opportunity to add a
new block is controlled in a round robin fashion, thereby eliminating the need
to perform a computationally intensive PoW process. Any transactions that are
broadcast to the P2P network are signed by the entity that created the transac-
tion, and can be verified by all other nodes by downloading the public key of the
10 Sarang Chaudhari, Michael Clear, Philip Bradish, and Hitesh Tewari
Threshold FAR FRR
0.25 3.99 64.26
0.26 6.35 57.35
0.27 9.49 49.63
0.28 13.92 43.79
0.29 19.60 36.47
0.3 26.23 30.79
0.31 34.01 25.10
0.32 42.30 19.33
0.33 50.91 16.00
0.34 59.04 11.94
0.35 67.05 8.53
Table 2: FAR & FRR for the CASIA-Iris-Interval Data Set
signer from the ledger itself. An example of distributed ledger technology that
fulfills the above requirements is MultiChain [9].
5.1 Interface
We now describe an abstract interface for the permissioned blockchain that cap-
tures the functionality we need. Consider a set of parties ˆ
P. A subset of parties
Pare authorized to write to the blockchain. Each party P Phas a se-
cret key skPwhich it uses to authenticate itself and gain permission to write to
the blockchain. How a party acquires authorization is beyond the scope of this
paper. For our purposes, the permissioned blockchain consists of the following
Blockchain.Broadcast(P,skP,tx): On input a party identifier Pthat identifies
the sending party, a secret key skPfor party Pand a transaction tx (whose
form is described below), then broadcast the transaction tx to the peer-to-
peer network for inclusion in the next block. The transaction will be included
iff P P.
Blockchain.AnonBroadcast(skP,tx) : On input a secret key skPfor a party P
and a transaction tx, then anonymously broadcast the transaction tx to the
peer-to-peer network for inclusion in the next block. The transaction will be
included iff P P.
Blockchain.GetNumBlocks(): Return the total number of blocks currently in
the blockchain.
Blockchain.RetrieveBlock(blockNo): Retrieve and return the block at index
blockNo, which is a non-negative integer between 0 and Blockchain.GetNumBlocks()
A transaction has the form (type,payload,party,signature). A transaction in an
anonymous broadcast is of the form (type,payload,,). The payload of a trans-
action is interpreted and parsed depending on its type. In our application, there
Framework for a DLT Based COVID-19 Passport 11
are two permissible types: ’rec’ (a record transaction which consists of a pair (ID,
record)) and ’hscan’ (biometric hash transaction which consists of a hash of an
iris feature vector). This will become clear from context in our formal descrip-
tion of our framework in the next section which makes use of the above interface
as a building block. The final point is that a block is a pair (hash,transactions)
consisting of the hash of the block and a set of transactions {txi}i[`].
6 Our Framework
6.1 Overview
In this section we provide a formal description of our proposed framework which
makes use of the building blocks presented in the previous sections. Our proposed
system utilises a two-factor authentication mechanism to uniquely identify an
individual on the blockchain. The parameters required to recreate an identifier
are based on information that “one knows” and biometric information that “one
Fig. 2: Algorithm Workflow
Figure 2 describes the overall algorithm that we employ in our proposed
system. When a user presents themselves to an entity or organisation partic-
12 Sarang Chaudhari, Michael Clear, Philip Bradish, and Hitesh Tewari
ipating in the system, they are asked for their DoB(dd/mm/yyyy) and Gen-
der(male/female/other). In addition, the organization captures a number of
scans of the user’s iris, and creates a hash H1(fv) from the feature vector ex-
tracted from the “best” biometric scan data. Our system can combine the user’s
DoB and Gender with H1(fv) to generate a unique 256-bit identifier (ID) for
the user:
ID =H2(DoB || Gender || H1(fv)) (2)
The algorithm tries to match the calculated hash H1(fv) with existing “anony-
mous” hashes that are stored on the blockchain. It may get back a set of hashes
that are somewhat “close” to the calculated hash. In that case the algorithm
concatenates each returned hash (Matchi) with the user’s DoB and Gender
to produce f
ID. It then tries to match f
ID with an ID in a vaccination record
transaction on the blockchain.
If a match is found then the user is already registered on the system and
has at least one vaccination record. At this point we may just wish to retrieve
the user’s records or add an additional record, e.g. when a booster dose has
been administered to the user. However if we go through the set of returned
matches and cannot match f
ID to an existing ID in a vaccination record on the
blockchain, i.e. this is the first time the user is presenting to the service, then we
store the iris scan hash data H1(fv) as an anonymous record on the blockchain,
and subsequently the ID and COVID-19 vaccination details for the user as
a separate transaction. In each case the transaction is broadcast at a random
interval on the blockchain peer-to-peer (P2P) network for it to be verified by
other nodes in the system, and eventually added to a block on the blockchain.
Uploading the two transactions belonging to a user at random intervals ensures
that the transactions are stored on separate blocks on the blockchain, and an
attacker is not easily able to identify the relationship between the two.
Figure 3 shows a blockchain in which there are three anonymous transactions
(i.e. Hash of Scan Data) and three COVID-19 vaccination record transactions
stored on the blockchain pertaining to different users. The reader is referred to
Section 4 for more details on how the hash is calculated in our system. Note
that the storage of the anonymous hash data has to be carried out only once
per registered user in the system.
6.2 Formal Description
We present a formal description of our framework in Figure 4 and Figure 5. Note
that the algorithms described in these figures are intended to formally describe
the fundamental desired functionality of our framework and are so described for
ease of exposition and clarity; in particular, they are naive and non-optimized,
specifically not leveraging more efficient data structures as would a real-world
Let Hbe a family of collision-resistant hash functions. The algorithms in
Figure 4 are stateful (local variables that contain retrieved information from
Framework for a DLT Based COVID-19 Passport 13
Fig. 3: Blockchain Structure
the blockchain are shared and accessible to all algorithms). Furthermore, the
parameters tuple params generated in Setup is an implicit argument to all other
The algorithms invoked by the algorithms in Figure 4 can be found in Fig-
ure 5.
7 Conclusions and Future Work
In this paper we have detailed a framework to build a global vaccination passport
using a distributed ledger. The main contribution of our work is to combine a
Locality-sensitive hashing mechanism with a blockchain to store the vaccination
records of users. A variant of the SimHash LSH function is used to derive an
identifier that leaks no personal information about an individual. The only way
to extract a user’s record from the blockchain is by the user presenting themselves
in person to an authorised entity, and providing an iris scan along with other
personal data in order to derive the correct user identifier. However, our research
has raised many additional challenges and research questions whose resolution
require further investigation and experimentation, intended for future work. First
and foremost, we need to improve the accuracy of the Iris.ExtractFeatureVector
algorithm (e.g: deciding whether to use type1or type2template masking) and
to accurately compute the entropy of the feature vectors.
Furthermore, our variant of the SimHash algorithm, referred to in this paper
as S3Hash, requires further analysis and evaluation, especially with respect to
the domain of the random vectors ri, which are restricted to be ternary in this
paper. Additionally, we must choose a suitable blockchain. Finally, the overall
protocol would benefit from a thorough security analysis where not just privacy
but other security properties are tested.
The blockchain based mechanism that we have proposed can also be used as
ageneralised healthcare management system [6, 12] with the actual data being
stored off-chain for the purpose of efficiency. Once a user’s identifier has been
recreated it can be used to pull all records associated with the user, thereby re-
14 Sarang Chaudhari, Michael Clear, Philip Bradish, and Hitesh Tewari
Algorithm Setup(1λ)
ri${−1,0,1}nfor i∈ {1,...,m}for i[m].
R← {r1,...,rm}
numBlocks 0
ids ← ∅
records ← ∅
hscans ← ∅
Return params := (H1, H2)
Algorithm AddRecord(P,skP,dob,gender,scan,record)
ID Authenticate(dob,gender,scan)
If ID =:
ID Enroll(P,skP,dob,gender,scan,record)
payload (ID,record)
tx (’rec’,payload,P, σ)
records records ∪ {(ID,record)}
Algorithm FetchRecords(dob,gender,scan)
ID Authenticate(dob,gender,scan)
If ID =:
results ← {record : (ID,record)records}
Return results
Fig. 4: Our Framework for a COVID-19 Passport
trieving their full medical history. We are in the middle of developing a prototype
implementation of the system and hope to present the results of our evaluation
in a follow-on paper. At some time in the future, we hope to trial the system in
the field, with the hope of rolling it out on a larger scale. Our implementation
will be made open source.
1. S. Charikar. Similarity estimation techniques from rounding algorithms. In Pro-
ceedings of the 34th Annual ACM Symposium on Theory of Computing, pages
380–388, 2002.
2. Chinese Academy Sciences’ Institute of Automation (CASIA) - Iris Image
Framework for a DLT Based COVID-19 Passport 15
3. COVID-19 Dashboard by the Center for Systems Science and Engineering (CSSE)
at Johns Hopkins University (JHU).
4. T. M. Dang, L. Tran, T. D. Nguyen, and D. Choi. Fehash: Full entropy hash for face
template protection. In Proceedings of the IEEE/CVF Conference on Computer
Vision and Pattern Recognition (CVPR) Workshops, June 2020.
5. J. Daugman. Statistical richness of visual phase information: Update on recognizing
persons by iris patterns. International Journal of Computer Vision, 45:25–38, 2001.
6. M. Hanley and H. Tewari. Managing lifetime healthcare data on the blockchain.
In 2018 IEEE SmartWorld, Ubiquitous Intelligence & Computing, Advanced
& Trusted Computing, Scalable Computing & Communications, Cloud & Big
Data Computing, Internet of People and Smart City Innovation, pages 246–251,
Guangzhou, 2018.
7. L. Masek. Recognition of human iris patterns for biometric identification. Final
Year Project, The School of Computer Science and Software Engineering, The
University of Western Australia, 2003.
8. L. Masek and P.Kovesi. Matlab source code for a biometric identification system
based on iris patterns. The School of Computer Science and Software Engineering,
The University of Western Australia, 2003.
9. Multichain.
10. A. L. Phelan. Covid-19 immunity passports and vaccination certificates: scientific,
equitable, and legal challenges. The Lancet, 395(10237):1595 – 1598, 2020.
11. C. Rathgeb and A. Uhl. A survey on biometric cryptosystems and cancelable
biometrics. EURASIP J. Information Security, 2011:3, 2011.
12. H. Tewari. Blockchain research beyond cryptocurrencies. IEEE Communications
Standards Magazine, 3(4):21–25, Dec. 2019.
13. World Health Organization.
16 Sarang Chaudhari, Michael Clear, Philip Bradish, and Hitesh Tewari
Algorithm Authenticate(dob,gender,scan)
fv Iris.ExtractFeatureVector(scan)
hscan H2(fv)
ID H1(dob kgender khscan)
If ID ids:
Return ID
For each hhscans:
dDist(hscan, h)
ID H1(dob kgender kh)
ID ids:
Algorithm Enroll(P,skP,dob,gender,scan,initRecord)
fv Iris.ExtractFeatureVector(scan)
hscan H2(fv)
ID H1(dob kgender khscan)
payload (ID,initRecord)
tx (’rec’,payload,P, σ)
Queue execution of Blockchain.AnonBroadcast(skP,tx0)
after time t
ids ids ∪ {ID}
hscans hscans ∪ {hscan}
records records ∪ {(ID,initRecord)}
Return ID
Algorithm Sync()
newNumBlocks Blockchain.GetNumBlocks()
If newNumBlocks >numBlocks:
For numBlocks i < newNumBlocks:
block Blockchain.RetrieveBlock(i)
For each tx transactions:
If type = ’rec’:
ids ids ∪ {ID}
records records ∪ {(ID,record)}
Else if type = ’hscan’:
hscan payload
hscans hscans ∪ {hscan}
numBlocks newNumBlocks
Fig. 5: Additional Algorithms Used By Our Framework
... Others investigated the potential use of different technologies and approaches such as IoT (Ennafiri & Mazri, 2020); big data (Lv, Ma, Li, & Wu, 2021); Blockchain, AI, and IoMT ; collaborative city digital twins (Pang, Huang, Xie, Li, & Cai, 2021); and smart city networks and infrastructure (Allam & Jones, 2020). There are also some studies discussing methods for creating vaccine passports (Chaudhari, Clear, & Tewari, 2020) and improved vaccine delivery supply chain (Weintraub et al., 2020). ...
... In Alanazi (2020) the author discusses a wide range of applications for blockchain for smart health and Healthcare 4.0 and in the authors discuss the value of a general adoption to address the issues of trust and privacy in Healthcare 4.0 applications. Specific examples using blockchain for Healthcare 4.0 include: UAV path planning during the pandemic (Aggarwal, Kumar, Alhussein, & Muhammad, 2021); creating trusted medical records (Bodkhe, Tanwar, Bhattacharya, & Verma, 2021); securing remote patient monitoring Aguiar et al., 2020;Alafif et al., 2021;Alanazi, 2020;Allam & Jones, 2020;Bharadwaj et al., 2021;Bishop & Leigh, 2020;Bodkhe et al., 2021;Chakravarty et al., 2021;Chau et al., 2020;Chaudhari et al., 2020;Chettri et al., 2020;Defendi et al., 2021;Ennafiri & Mazri, 2020;Hathaliya, Sharma, Tanwar, & Gupta, 2019;He et al., 2021;Ho, 2021;Jamshidi et al., 2021;Johansson et al., 2018;Kiszewski et al., 2021;Kwok, 2021;Lv et al., 2021;Mbunge, 2020;Mbunge et al., 2021;Nasajpour et al., 2020;Pang et al., 2021;Pavli & Maltezou, 2021;Romette et al., 2018;Sosa et al., 2021;Strizova et al., 2021;Tarfaoui et al., 2020;Udugama et al., 2020;Weintraub et al., 2020;Zhang et al., 2020;Zimmerling & Chen, 2021); creating a telesurgery framework ; and protecting electronic health records . ...
... Examples include the lack of and/or difficulty of finding adequate data sources and clean data; the abundance of irrelevant, incorrect, and fragmented data; difficulties sharing data sources across organizations and/or countries; non-standardized formats, organization and sharing protocols; unclear regulations on data collection, storage, sharing and use; the need to achieve secure and privacy-supporting sharing and use of data; ownership and control of user data; and limited trust in the available data and its uses. Other issues appearing consistently include the privacy issues as in Bharadwaj et al. (2021), Chaudhari et al. (2020), Sosa et al. (2021), Weintraub et al. (2020; Collaboration capabilities and tools (Bharadwaj et al., 2021;He et al., 2021;Pang et al., 2021); experience in medical research coupled with technology aspects (Chakravarty et al., 2021;Lv et al., 2021); ethics, equity, and human factor issues were discussed in Chaudhari et al. (2020), He et al. (2021), Lv et al. (2021), Pavli and Maltezou (2021), Sosa et al. (2021); and high performance computing and communication capabilities were also highlighted in Alafif et al. (2021), Bharadwaj et al. (2021), Chakravarty et al. (2021), Defendi et al. (2021), Jamshidi et al. (2021), Nasajpour et al. (2020. ...
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Seldom do we think that we will witness something such as COVID-19 in our lifetime. We have witnessed SARS before, and we have grown reading the history of Bubonic plague, Cholera, Chicken Pox, and Typhoid. We have also felt proud learning the victory of our forefathers over these diseases. However, when the First COVID patient was found in late 2019 in the Wuhan province of China, even in our worst nightmare, we did not think it would turn into the most devastating pandemic in human history so far. Being one of the closest neighbors of China, the first COVID patient in India was identified on January 27, 2020. Just 3days later, on January 30, 2020, the World Health Organization (WHO) declared the 2019–20 Novel Corona Virus Diseases (COVID-19) epidemic a Public Health Emergency of International Concern (PHEIC).
... Our system takes a scanned image of an iris as the input and outputs a binary feature vector (fv). Masek's technique works on grey-scale eye images, which are processed in order to extract the binary template [11]. Figure 2 shows the overall process of the iris template extraction technique. ...
... This will ensure that information about the users' irises cannot be leaked from the stored hashes. In [11], the authors show that the S3Hash (a variant of Charikar's Simhash) algorithm is input hiding, provided the entropy of the input vector is sufficiently larger than the size of the hash. ...
Full-text available
Vaccination passports are being issued by governments around the world in order to open up their travel and hospitality sectors. Civil liberty campaigners on the other hand argue that such mandatory instruments encroach upon our fundamental right to anonymity, freedom of movement, and are a backdoor to issuing “identity documents” to citizens by their governments. We present a privacy-preserving framework that uses two-factor authentication to create a unique identifier that can be used to locate a person’s vaccination record on a blockchain, but does not store any personal information about them. Our main contribution is the employment of a locality sensitive hashing algorithm over an iris extraction technique, that can be used to authenticate users and anonymously locate vaccination records on the blockchain, without leaking any personally identifiable information to the blockchain. Our proposed system allows for the safe reopening of society, while maintaining the privacy of citizens.KeywordsLocality-sensitive hashBiometric hashBlockchainVaccination passport
... Most solutions are proprietary and opaque to the public. Thus, without loss of generality, we focus on 10 published literature listed in [60], X.509 [61], and customized formats [62] [63]. Among them, VC is the major format representing health certificates, which combines semantic web standards with decentralized identifier (DID) schemes [64]. ...
... On the other hand, [74] criticizes the security weakness of VC and DID, as they are usually based on under-specified and non-standardized documents, leaving immunity passports vulnerable to some types of cyber-attack. [62] proposes a novel two-factor authentication framework by encoding one's biometric information with locality-sensitive hashing. As for regulations, [9] and [58] claim to comply with GDPR, a regulation for data protection and privacy in EU and EEA. ...
Full-text available
Since 2020, the COVID-19 pandemic severely disrupted regular off-line business activities. This unprecedented situation inspires the valuable research on facilitating off-line business under pandemics. In this article, we conceptualized the problem as travel management in pandemic (TMiP) and analyzed it from the technological perspective. Enabling travel in a pandemic not only needs a health certificate to prove that the traveler is safe but also entry/exit permissions from both the origin and the destination regions, determined by the local situation and measures. Thus, TMiP is related to technical, social, economic, and administrative factors. By conducting a review on the literature covering the health certificate technology, its adoption in practice, and the exchange system technology published during the COVID-19 pandemic, we learned about their usefulness and limitations in TMiP. Second, we analyzed the review outcomes to infer the six distinctive technical challenges of TMiP. Third, we analyzed the feasibility of referential solutions to these challenges and showed their applicability and limitations. Finally, we offered the perspectives on new TMiP solutions and concluded that they rely on adapting existing solutions, creating new ones, and integrating all of them. We also presented future research directions in a holistic view of TMiP technical solutions. Overall, the findings of the study will stimulate more research on a more coordinated, comprehensive, and intelligent TMiP solution. We also hope this article can help practitioners to restart economies in a pandemic.
... Carefully analyzing the extant solutions reveals the reliance on centralized databases under the administration of organizations with vested interests, inadequacies in user privacy protection mechanisms as unraveled by a recent study, 26 no global solution allowing verifiability in any country to alleviate the need for re-testing upon arrival as virtually all extant solutions are private blockchain-based for specified jurisdictions, [8][9][10][11][12][13]15,17,18,21 impractical assumptions requiring travelers to deploy and manage smart contracts (SCs), inherent blockchain-related complexities that potentially would be overwhelming for travelers, and no provision for an update mechanism when pertinent data of travelers/patients are stored on blockchain-an indispensable feature 27 since test/vaccination status from traveler's electronic health records (EHR) is dynamic. With healthcare being the industry with the highest number of internal bad actors and almost half of healthcare breaches emanating from within the same organization, 28 centralized databases and entrusting organizations with healthcare data raise security concerns including privacy breaches, data loss, and data integrity. ...
... Noteworthy is the fact that there exist other propositions based on private blockchain for specified jurisdictions. [8][9][10][11][12][13]15,17,18 Recall there exist non-blockchain-based solutions. However, all such solutions are characterized by: use of centralized databases under an organization's or state's control or country/regional-based (UK, US, Australia, China, Israel, France, Africa, EU etc.). ...
COVID‐19 pandemic undoubtedly lingers on and has brought unprecedented changes globally including travel arrangements. Blockchain‐based solutions have been proposed to aid travel amid the pandemic hap. Presently, extant solutions are country or regional‐based, downplay privacy, non‐responsive, often impractical, and come with blockchain‐related complexities presenting technological hurdle for travelers. We therefore propose a solution namely, Borderless to foster global travel allowing travelers and countries collaboratively engage in a secure adaptive proof protocol dubbed Proof‐of‐COVID‐19 status a number of arbitrary statements to ascertain the fact that the traveler poses no danger irrespective of the country located. As far as we know, this is first of its kind. Borderless is implemented as a decentralized application leveraging blockchain as a trust anchor and decentralized storage technology. Security analysis and evaluation are performed proving security, privacy‐preservation, and cost‐effectiveness along with implementation envisioning it as a blueprint to facilitate cross‐border travel during the present and future pandemics. Our experimental results show it takes less than 60 and 3 s to onboard users and perform proof verification respectively attesting to real usability scenarios along with the traits of arbitrary proofs to aid responsiveness to the dynamics of pandemics and blockchain abstraction from travelers.
... Instead, most of the concepts presented rely on decentralised storage of the veri cation data on citizens' smartphones. The integrity of the proof is guaranteed either by electronic signatures [4,27] or the central storage of checksums of the proof on a distributed ledger [28][29][30]. This differentiates veri cation systems in scienti c publications to those operated by states which are mainly based on electronic signatures [3]. ...
Full-text available
Purpose Physicians and scientists hope to gain new insights from health data to improve medical care and optimize costs in the healthcare sector. However, data protection laws in Europe often impose limits on the use of patient data. During the COVID-19 pandemic the exercise of all civil rights and liberties depends on successful vaccinations, negative tests, and recovery from the disease. Digital proof thereof was of particular importance for participation in social life. This research project aims to create a system concept for vaccination, testing, and recovery proof called P3VT (Privacy Preserving Pass for Vaccination and Testing), which makes all collected data anonymously available in real time to scientists as well as to political pandemic management. Methods Based on the Design Science Research methodology (DSR) [1], P3VT is the artifact created by the research project. It was developed over several iterations, consistently taking into consideration the goals of privacy-by-design, data minimisation and transparency of the EU-GDPR. Expert interviews have been conducted to validate the system from a medical, technical and data protection perspective. Results By using distributed ledger technology and distributed identities, P3VT offers the following advantages compared to the EU digital COVID certificate: · Pseudonymous proof of vaccination, testing, and recovery, reducing the misuse of sensitive personal data · Transparency on type, time, and purpose of proof increases users' trust · Use of anonymous vaccination and testing data to improve regulatory pandemic management, as well as research · Flexible specification of proof conditions based on the latest epidemiological findings or individual requirements · Elimination of manual ID checks during the verification process. Conclusion P3VT provides a novel combination of unforgeable pseudonymous proof of COVID-19 vaccination, testing, and recovery with simultaneous provision of anonymous data for research purposes and regulatory pandemic management. It is therefore an example of how the comprehensive provision of health data for research purposes can be combined with high data protection requirements. Further areas of application are conceivable.
... On the other hand, the human factor plays a strong role in making, or breaking, the Healthcare 4.0 vision. Ethics, equity, and human factor issues were discussed in [56][63] [64][65] [69]. Politics, governments, private/public sector involvement, intellectual property protection, and public trust are also important. ...
In this paper, a system is proposed which uses blockchain technology in healthcare. In this system, patients can access their health records anytime from anywhere. Moreover, the patients’ health records are put into the blockchain anonymously. Whenever a patient visits a healthcare professional, the authorized entity filters patients’ medical report out by eliminating the patients’ sensitive information. Then, the filtered medical data are put into an off-chain database, while the address of the data is put into the blockchain with an assigned pseudo random identity of the patient. Thus, there are multi pseudo random identities for each patient. Unlike previous studies where the patients’ identities/reports were linkable, in the proposed protocol the patients’ identities are not linkable. The proposed system can also be used to show patients’ health status to some entities when a pandemic happens (e.g. COVID-19). During the COVID-19 pandemic, the patients are required to show their series of vaccinations before they travel internationally/nationally or participate in some social events. To travel or join some events, the patient needs to show only a partial medical history to the security guard without leaking any private information. Furthermore, once the anonymous medical data are put into the off-chain database, the data can be used for data mining and machine learning.
Various international initiatives have been launched in 2021 to generate digital vaccination certificates to address challenges faced by travellers exposed during COVID19. While COVID19 has impacted multiple industries where alternate solutions have emerged at competing rates, airline industry in particular have been hit hard due to highly regulated protocol. Owing to its unique characteristics of transparency and decentralization, block chain technology provides an opportunity to create smart solutions for travel industry. We present a solution that describes a scaled, blockchain-based infrastructure for exchanging COVID-19 pandemic travellers’ history and vaccination status in a secure manner. The proposed approach ensures the travellers are coronavirus-free and check their COVID 19 history and vaccination status across the borders and immigration in particular. The framework employs a permission blockchain and Proof of Authority to check vaccination status on airports using the smart contract. It provides a distributed infrastructure for national and international healthcare systems, to check digital vaccination certificate and individual vaccination history and their verification by relevant stakeholders, such as airport securities, health authorities, governments, border control authorities and airlines.KeywordsVaccination certificateCOVID-19BlockchainProof of authority
COVID-19 vaccinations have been approved for public immunization and are going through clinical trials. Vaccinating a billion people of India is a huge challenge. Tracing, last mile delivery, data privacy, double spend of dosage, and multiparty authorization pose serious challenges for providing COVID-19 vaccines. Policies have been framed on who gets the access to the vaccine. However, there is a need of a technological solution to create an efficient vaccine distribution or delivery system. This paper proposes a novel blockchain enabled vaccine delivery system in the context of India. A consortium blockchain has been proposed which has different participants, like the UIDAI, healthcare facilities, pharmaceutical supply chain, etc. These participants are responsible for authenticating the beneficiary of the COVID-19 vaccine. Sequence diagram of how the beneficiary is authorized to access the vaccine has been proposed. © 2022, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.
Full-text available
One of the key requirements of a properly functioning digital society is the implementation of a decentralized identity management scheme through which the identity of every citizen can be uniquely determined. Specifically, we believe what is required is for a PKI to be deployed at a global scale. A PKI consists of a collection of digital certificates that cryptographically bind an individual's identity to their public key. In this article, we present an overview of our recent work in the areas of identity management and privacy, with specific emphasis on the deployment of a blockchain backed PKI. Once a PKI is in place, we are in a position to perform a number of common network tasks much more securely and efficiently than we can do currently.
Conference Paper
Full-text available
The widespread adoption of fax machines in the 1980s revolutionised everyday communications. It was quickly adopted as the standard form of communication across the globe. Since then, the internet has replaced fax as a truly global form of instant communication. However, the fax machine still reigns as the primary form of communication in a number of industries, healthcare being one of them. This paper presents a system that uses a blockchain and an off-chain centralised data storage to give patients and medical professionals instant access to their medical records from anywhere. By assigning each medical record a pseudo anonymous identifier, a second layer "blockchain" for each user can be created allowing for the rapid collection and querying of data. The off-chain pseudo anonymous data storage allows for the data to remain unencrypted enabling the rapid generation of anonymous medical datasets which can be used for machine learning and data mining on the data, potentially bringing many benefits to the healthcare industry.
Full-text available
Form a privacy perspective most concerns against the common use of biometrics arise from the storage and misuse of biometric data. Biometric cryptosystems and cancelable biometrics represent emerging technologies of biometric template protection addressing these concerns and improving public confidence and acceptance of biometrics. In addition, biometric cryptosystems provide mechanisms for biometric-dependent key-release. In the last years a significant amount of approaches to both technologies have been published. A comprehensive survey of biometric cryptosystems and cancelable biometrics is presented. State-of-the-art approaches are reviewed based on which an in-depth discussion and an outlook to future prospects are given.
An interesting relationship between rounding algorithms used for rounding fractional solutions of LPs and vector solutions of SDPs on the one hand, and the constructions of locality sensitive hash functions for interesting classes of objects, on the other was demonstrated. Thus, rounding algorithms yielded new constructions of locality sensitive hash functions that were not previously known. Conversely, locality sensitive hash functions lead to rounding algorithm.
A biometric system provides automatic identification of an individual based on a unique feature or characteristic possessed by the individual. Iris recognition is regarded as the most reliable and accurate biometric identification system available. Most commercial iris recognition systems use patented algorithms developed by Daugman, and these algorithms are able to produce perfect recognition rates. However, published results have usually been produced under favourable conditions, and there have been no independent trials of the technology. The work presented in this thesis involved developing an 'open-source' iris recognition system in order to verify both the uniqueness of the human iris and also its performance as a biometric. For determining the recognition performance of the system two databases of digitised greyscale eye images were used.
Conference Paper
(MATH) A locality sensitive hashing scheme is a distribution on a family $\F$ of hash functions operating on a collection of objects, such that for two objects x,y, PrhεF[h(x) = h(y)] = sim(x,y), where sim(x,y) ε [0,1] is some similarity function defined on the collection of objects. Such a scheme leads to a compact representation of objects so that similarity of objects can be estimated from their compact sketches, and also leads to efficient algorithms for approximate nearest neighbor search and clustering. Min-wise independent permutations provide an elegant construction of such a locality sensitive hashing scheme for a collection of subsets with the set similarity measure sim(A,B) = \frac{|A &Pgr; B|}{|A &Pgr B|}.(MATH) We show that rounding algorithms for LPs and SDPs used in the context of approximation algorithms can be viewed as locality sensitive hashing schemes for several interesting collections of objects. Based on this insight, we construct new locality sensitive hashing schemes for:A collection of vectors with the distance between → \over u and → \over v measured by Ø(→ \over u, → \over v)/π, where Ø(→ \over u, → \over v) is the angle between → \over u) and → \over v). This yields a sketching scheme for estimating the cosine similarity measure between two vectors, as well as a simple alternative to minwise independent permutations for estimating set similarity.A collection of distributions on n points in a metric space, with distance between distributions measured by the Earth Mover Distance (EMD), (a popular distance measure in graphics and vision). Our hash functions map distributions to points in the metric space such that, for distributions P and Q, EMD(P,Q) &xie; Ehε\F [d(h(P),h(Q))] &xie; O(log n log log n). EMD(P, Q)..
Algorithms first described in 1993 for recognizing persons by their iris patterns have now been tested in several public field trials, producing no false matches in several million comparison tests. The underlying recognition principle is the failure of a test of statistical independence on texture phase structure as encoded by multi-scale quadrature wavelets. The combinatorial complexity of this phase information across different persons spans about 244 degrees of freedom and generates a discrimination entropy of about 3.2 bits/mm2 over the iris, enabling real-time decisions about personal identity with extremely high confidence. This paper reviews the current algorithms and presents the results of 2.3 million comparisons among eye images acquired in trials in Britain, the USA, and Japan, and it discusses aspects of the process still in need of improvement.
Recognition of human iris patterns for biometric identification. Final Year Project, The School of Computer Science and Software Engineering
  • L Masek
L. Masek. Recognition of human iris patterns for biometric identification. Final Year Project, The School of Computer Science and Software Engineering, The University of Western Australia, 2003.