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QUANTUM CRYPTOGRAPHY AND ITS ADVANCES
QUANTUM CRYPTOLOGY AND ITS ADVANCES
Hridya Ramesh
Mrs.Malini Thomas
Asst.Professor
Ms.Sreekala V
Lecturer
Department of Electronics & Communication Engineering
Sahrdaya College of Engineering & Technology, Kodakara, P.B.No.17, Thrissur, 680684.
ABSTRACT
INTRODUCTION
In this era, the need for security has attained
In our contemporary world,security has
paramount importance. As more of our sensitive information
attained paramount importance. The necessity for security
is stored in computers the need of data security becomes
has increased beyond everything. And that is why ways of
increasingly important. Protecting this information against
staying secure has to developed and implemented.
unauthorized usage is therefore a major concern for both
operating systems and users alike. Cryptography is one such
The concept of cryptology dates back to B.C.
method of safeguarding sensitive data from being stolen or
It’s a method used to encrypt our data securely. Though
intercepted by unwanted third parties. Traditional cryptology
present day security systems offer a good level of
is certainly clever, but as with all encoding methods in code-
protection, they are incapable of providing a "trust worthy"
breaking history, it's being phased out.
environment and are vulnerable to unexpected attacks.
Many organizations posses valuable information they
Quantum Cryptology is based on physics and not
guard closely. As more of this information is stored in
mathematics, unlike the present ones. By harnessing the
computers the need of data security becomes increasingly
unpredictable nature of matter at the quantum level, physicists
important.
have figured out a way to exchange information on secret keys.
unauthorized usage is therefore a major concern for both
Attaching information to the photons spin is the essence of
operating systems and users alike. Cryptography is one
Quantum Cryptology.In brief, the processes of encoding
such method of safeguarding sensitive data from being
(cryptography) and decoding (crypto analysis) information or
stolen or intercepted by unwanted third parties. Traditional
messages (called plaintext) into an otherwise meaningless data
cryptology is certainly clever, but as with all encoding
(cipher text) combined are cryptology.and when the keys used
methods in code-breaking history, it's being phased out.
Protecting
this
information
against
for this process are photons, it’s called Quantum Cryptology.
Quantum Cryptology is based on physics and
not mathematics, unlike the present ones. By harnessing
the unpredictable nature of matter at the quantum level,
physicists have figured out a way to exchange information
on secret keys.
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QUANTUM CRYPTOGRAPHY AND ITS ADVANCES
The
foundation
of
quantum
physics
is
the
unpredictability factor. This unpredictability is pretty much
defined by Heisenberg's Uncertainty Principle. This principle
says, essentially, that it's impossible to know both an object's
position and velocity -at the same time. But when dealing with
photons for encryption, Heisenberg's principle can be used to
our advantage. To create a photon, quantum cryptographers use
LEDs , a source of unpolarized light, capable of creating just
one photon at a time, which is how a string of photons can be
created, rather than a wild burst.
SECURITY
NEED FOR SECURITY
Through the use of polarization filters, we can force
the photon to take one state or another -- or polarize it. The
thing about photons is that once they're polarized, they can't be
accurately measured again, except by a filter like the one that
From a security perspective computer systems
have 3 general goals with corresponding threats to them as
listed below:
initially produced their current spin.
So if a photon with a vertical spin is measured through a
diagonal filter, either the photon won't pass through the filter or
the filter will affect the photon's behavior, causing it to take a
diagonal spin. In this sense, the information on the photon's
original polarization is lost, and so, too, is any information
attached to the photon's spin.
Attaching information to the photons spin is the
The first one data confidentiality is concerned
with secret data remaining secret. More specifically if the
owner of some data has decided that the data should be
available
only to certain people and no others, then the system
should guarantee that release of data to unauthorized
people does not occur. Another aspect of this is individual
privacy.
essence of Quantum Cryptology. Quantum cryptography uses
photons to transmit a key. Once the key is transmitted, coding
and encoding using the normal secret-key method can take
place.
The second goal, data integrity, means that
unauthorized users should not be able to modify any data
without the owner's permission. Data modification in this
context includes not only changing the data, but also
In brief, the processes of encoding (cryptography)
and decoding (crypto analysis) information or messages (called
plaintext) into an otherwise meaningless data (cipher text)
combined are cryptology.and when the keys used for this
removing data and adding false data as well. Thus it is
very important that a system should guarantee that data
deposited in it remains unchanged until the owner decides
to do so.
process are photons, it’s called Quantum Cryptology.
The third goal, system availability, means that
nobody can disturb the system to make unstable. It must be
LITERATURE REVIEW
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QUANTUM CRYPTOGRAPHY AND ITS ADVANCES
able to ensure that authorized persons have access to the data
and do not suffer form denial of service.
Basically a virus is a piece of code that
replicates itself and usually does some damage. In a
sense the writer of a virus is also an intruder, often with
Types of Data Threats
high technical skills. In the same breath it must be said
that a virus need not always be intentional and can
Intruders:
simply be a code with disastrous run time errors. The
In security literature people who are nosing around places
difference between a conventional intruder and a virus
where they have no business being are called intruders or
is that the former refers to person who is personally
sometimes adversaries. Intruders can be broadly divided as
trying to break into a system to cause damage whereas
passive and active. Passive intruders just want to read the files
the latter is a program written by such a person and
they are not authorized to. Active intruders are more malicious
then released into the world hoping it causes damage.
and intend to make unauthorized changes to data. Some of the
The most common types of viruses are: executable
common
program viruses, memory resident viruses, boot sector
activities
indulged
by
intruders
are:
viruses, device driver viruses, macro viruses, source
Casual Prying: non-technical users who wish to read other
people's e-mail and
private
files
mostly do
code viruses, Trojan horses etc.
this.
Snooping: This term refers to the breaking of the security of
AN OVERVIEW OF SOME OF THE PRESENT
a shared computer system or a server. Snooping is generally
DAY DATA SECURITY SYSTEMS:
done as a challenge and is not aimed at stealing or
tampering
of
confidential
data.
User authentication:
Commercial Espionage: This refers to the determined
It is a method employed by the operating
attempts to make money using secret data. For example an
system or a program of a computer to determine the
employee in an organization can secure sensitive data and
identity of a user. Types of user authentication are:
sell it away to rival companies for monetary gains.
Authentication using passwords, authentication using
physical objects (like smart cards, ATM cards etc.),
It is very important that potential intruders (and their
authentication using biometrics (like Finger prints,
corresponding activities) are taken into consideration before
retinal
devising a security system. This is essential as the level of
recognition
threat and intended damage differ from one to another.
authentication are password cracking, duplication of
pattern
scan,
etc.).
signature
Inherent
analysis,
problems
of
voice
user
physical objects and simulation of biometrics by
artificial objects.
Virus:
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Anti-virus software:
3
QUANTUM CRYPTOGRAPHY AND ITS ADVANCES
An antivirus software scans every executable file on a
QUANTUM CRYPTOGRAPHY
computer's disk looking for viruses known in its database. It
then repairs, quarantines or deletes an infected files.
CRYPTOLOGY
However a clever virus can infect the anti-virus software
Cryptography is the method in which a message
itself. Some of the popular anti-virus soft wares are K7,
or file, called plain text,is taken and encrypted into
PCcillin, MCcafee,Eset Nod32 etc.
cipher text in such a way that only authorized people
know how to convert it back to plain text. There are
Firewalls:
limitless possibilities for keys used in cryptology. But
It is a method of preventing unauthorized access to a
there are only two widely used methods of employing
computer system often found in network computes. A
keys: public-key cryptology and secret-key cryptology.
firewall is designed to provide normal service to authorized
In both of these methods (and in all cryptology), the
users while at the same time preventing unauthorized users
sender (point A) is referred to as Alice. Point B is
from gaining access to the system. In reality they add a
known as Bob.
level of inconvenience to legal users and their ability to
control illegal access may be questionable. They also stop
In the public-key cryptology (PKC) method, a
ones computer from sending malicious software to another
user chooses two interrelated keys. He lets anyone who
computer.
wants to send him a message know how to encode it using
one key. He makes this key public. The other key he keeps
Cryptography:
to himself. In this manner, anyone can send the user an
Cryptography is the method in which a message or file,
encoded message, but only the recipient of the encoded
called plain text, is taken and encrypted into cipher text in
message knows how to decode it. Even the person sending
such a way that only authorized people know how to
the message doesn't know what code the user employs to
convert it back to plane text. This is done commonly in four
decode it.
ways:
The
other
usual
method
of
traditional
Secret key cryptography, public key cryptography, one way
cryptology is secret-key cryptology (SKC). In this method,
function cryptography and digital signatures.
only one key is used by both Bob and Alice. The same key
is used to both encode and decode the plaintext. Even the
algorithm used in the encoding and decoding process can
be announced over an unsecured channel. The code will
remain uncracked as long as the key used remains secret.
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QUANTUM CRYPTOGRAPHY AND ITS ADVANCES
Traditional cryptology is certainly clever, but as
listen in and gain information the users don't want that
with all encoding methods in code-breaking history, it's being
person to have. This is known in cryptology as the key
phased out.
distribution problem.
It's one of the great challenges of cryptology: To
Traditional Cryptology Problems
The keys used to encode messages are so long that it
keep unwanted parties - from learning of sensitive
information.
would take a trillion years to crack one using conventional
Quantum physics has provided a way around this problem.
computers. The problem with public-key cryptology is that it's
By harnessing the unpredictable nature of matter at the
based on the staggering size of the numbers created by the
quantum level, physicists have figured out a way to
combination of the key and the algorithm used to encode the
exchange information on secret keys.
message. These numbers can reach unbelievable proportions.
What's more, they can be made so that in order to understand
Quantum physics
each bit of output data, you have to also understand every other
Photons are some pretty amazing particles.
bit as well. This means that to crack a 128-bit key, the possible
They have no mass, they're the smallest measure of light,
numbers used can reach upward to the 1038 power. That's a lot
and they can exist in all of their possible states at once,
of possible numbers for the correct combination to the key. The
called the wave function. This means that whatever
keys used in modern cryptography are so large, in fact, that a
direction a photon can spin in -- say, diagonally, vertically
billion computers working in conjunction with each processing
and horizontally -- it does all at once. Light in this state is
a billion calculations per second would still take a trillion years
called unpolarized. This is exactly the same as if you
to definitively crack a key [source: Dartmouth College]. This
constantly moved east, west, north, south, and up-and-
isn't a problem now, but it soon will be.
down at the same time.
Current computers will be replaced in the near future
with quantum computers, which exploit the properties of
The
foundation
of
quantum
physics
is
the
physics on the immensely small quantum scale.Since they can
unpredictability factor. This unpredictability is pretty much
operate on the quantum level, these computers are expected to
defined by Heisenberg's Uncertainty Principle. This principle
be able to perform calculations and operate at speeds no
says, essentially, that it's impossible to know both an object's
computer in use now could possibly achieve. So the codes that
position and velocity -- at the same time. But when dealing with
would take a trillion years to break with conventional
photons for encryption, Heisenberg's principle can be used to our
computers could possibly be cracked in much less time with
advantage. To create a photon, quantum cryptographers use
quantum computers. This means that secret-key cryptology
LEDs -- light emitting diodes, a source of unpolarized light.
(SKC) looks to be the preferred method of transferring ciphers
LEDs are capable of creating just one photon at a time, which is
in the future. But SKC has its problems as well. The chief
how a string of photons can be created, rather than a wild burst.
problem with SKC is how the two users agree on what secret
Through the use of polarization filters, we can force the photon
key to use. The problem with secret-key cryptology is that
to take one state or another -- or polarize it. If we use a vertical
there's almost always a place for an unwanted third party to
polarizing filter situated beyond a LED, we can polarize the
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QUANTUM CRYPTOGRAPHY AND ITS ADVANCES
photons that emerge: The photons that aren't absorbed will emerge
on the other side with a vertical spin ( | ).
The thing about photons is that once they're
polarized, they can't be accurately measured again, except by a
filter like the one that initially produced their current spin. So if
a photon with a vertical spin is measured through a diagonal
filter, either the photon won't pass through the filter or the filter
will affect the photon's behavior, causing it to take a diagonal
spin. In this sense, the information on the photon's original
Fig. 2 Photons as keys.
polarization is lost, and so, too, is any information attached to
the photon's spin.
This is where binary code comes into play. Each
type of a photon's spin represents one piece of information
-- usually a 1 or a 0, for binary code. This code uses strings
of 1s and 0s to create a coherent message. For example,
1110010011 could correspond to h-e-l-l-o. So a binary
code can be assigned to each photon -- for example, a
photon that has a vertical spin ( | ) can be assigned a 1.
Alice can send her photons through randomly
chosen filters and record the polarization of each photon.
Fig 1 Polarization of photons.
She will then know what photon polarizations Bob should
receive. When Alice sends Bob her photons using an LED,
she'll randomly polarize them through either the X or the +
Using Quantum cryptology
Quantum cryptography uses photons to transmit a
key. Once the key is transmitted, coding and encoding
using the normal secret-key method can take place. But
how does a photon become a key? How do you attach
information to a photon's spin?
filters, so that each polarized photon has one of four
possible states: (|), (--), (/) or (\ ) . As Bob receives these
photons, he decides whether to measure each with either
his + or X filter -- he can't use both filters together. Keep
in mind, Bob has no idea what filter to use for each
photon, he's guessing for each one. After the entire
transmission, Bob and Alice have a non-encrypted
discussion about the transmission.
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QUANTUM CRYPTOGRAPHY AND ITS ADVANCES
The reason this conversation can be public is
translated into English, Spanish, Navajo, prime numbers or
because of the way it's carried out. Bob calls Alice and tells her
anything else the Bob and Alice use as codes for the keys
which filter he used for each photon, and she tells him whether
used in their encryption.
it was the correct or incorrect filter to use.
Their conversation may sound a little like this:
Bob: Plus
Alice: Correct
Bob: Plus
Alice: Incorrect
Bob: X
Alice: Correct
Since Bob isn't saying what his measurements are -only the type of filter he used -- a third party listening in on
their conversation can't determine what the actual photon
sequence is.
Fig 4.3 Interception Detection
Here's an example. Say Alice sent one photon as a ( /
) and Bob says he used a + filter to measure it. Alice will say
The goal of quantum cryptology is to thwart
"incorrect" to Bob. But if Bob says he used an X filter to
measure that particular photon, Alice will say "correct." A
person listening will only know that that particular photon
could be either a ( / ) or a ( ), but not which one definitively.
attempts by a third party to eavesdrop on the encrypted
message. In cryptology, an eavesdropper is referred to as
Eve.
In modern cryptology, Eve (E) can passively
Bob will know that his measurements are correct,
because a (--) photon traveling through a + filter will remain
polarized as a (--) photon after it passes through the filter.
After their odd conversation, Alice and Bob both
throw out the results from Bob's incorrect guesses. This leaves
Alice and Bob with identical strings of polarized protons. It my
look a little like this: -- / | | | / -- -- | | | -- / | … and so on. To
Alice and Bob, this is a meaningless string of photons. But
once binary code is applied, the photons become a message.
Bob and Alice can agree on binary assignments, say 1 for
photons polarized as ( \ ) and ( -- ) and 0 for photons polarized
like ( / ) and ( | ). This means that their string of photons now
intercept Alice and Bob's encrypted message -- she can get
her hands on the encrypted message and work to decode it
without Bob and Alice knowing she has their message.
Eve can accomplish this in different ways, such as
wiretapping Bob or Alice's phone or reading their secure emails.
Quantum cryptology is the first cryptology that
safeguards against passive interception. Since we can't
measure a photon without affecting its behavior,
Heisenberg's Uncertainty Principle emerges when Eve
makes her own eavesdrop measurements.
looks like this: 11110000011110001010. Which can in turn be
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QUANTUM CRYPTOGRAPHY AND ITS ADVANCES
Here's an example. If Alice sends Bob a series of
polarized photons, and Eve has set up a filter of her own to
photon has been measured by a third party, who
inadvertently altered it.
intercept the photons, Eve is in the same boat as Bob: Neither
has any idea what the polarizations of the photons Alice sent
Alice and Bob can further protect their
are. Like Bob, Eve can only guess which filter orientation
transmission by discussing some of the exact correct
(for example an X filter or a + filter) she should use to
results
measure the photons.
measurements. This is called a parity check. If the
after
they've
discarded
the
incorrect
chosen examples of Bob's measurements are all correct After Eve has measured the photons by randomly
- meaning the pairs of Alice's transmitted photons and
selecting filters to determine their spin, she will pass them
Bob's received photons all match up -- then their
down the line to Bob using her own LED with a filter set to
message is secure.
the alignment she chose to measure the original photon. She
Bob and Alice can then discard these discussed
does to cover up her presence and the fact that she intercepted
measurements and use the remaining secret measurements
the photon message. But due to the Heisenberg Uncertainty
as their key. If discrepancies are found, they should occur
Principle, Eve's presence will be detected.
in 50 percent of the parity checks. Since Eve will have
By measuring the photons, Eve inevitably altered
altered about 25 percent of the photons through her
some of them.Say Alice sent to Bob one photon polarized to
measurements, Bob and Alice can reduce the likelihood
a ( -- ) spin, and Eve intercepts the photon. But Eve has
that Eve has the remaining correct information down to a
incorrectly chosen to use an X filter to measure the photon. If
one-in-a-million chance by conducting 20 parity checks
Bob randomly (and correctly) chooses to use a + filter to
measure the original photon, he will find it's polarized in
PROBLEMS OF QUANTUM CRYPTOLOGY
either a ( / ) or ( \) position. Bob will believe he chose
Despite all of the security it offers, quantum
incorrectly until he has his conversation with Alice about the
cryptology also has a few fundamental flaws. Chief among
filter choice.
these flaws is the length under which the system will
work: It’s too short.
After all of the photons are received by Bob, and
The original quantum cryptography system,
he and Alice have their conversation about the filters used to
built in 1989 by Charles Bennett, Gilles Brassard and John
determine the polarizations, discrepancies will emerge if Eve
Smolin, sent a key over a distance of 36 centimeters
has intercepted the message. In the example of the ( -- )
[source: Scientific American]. Since then, newer models
photon that Alice sent, Bob will tell her that he used a +
have reached a distance of 150 kilometers (about 93
filter.
miles).
Alice will tell him this is correct, but Bob will
But this is still far short of the distance
know that the photon he received didn't measure as ( -- ) or ( |
requirements needed to transmit information with modern
). Due to this discrepancy, Bob and Alice will know that their
computer and telecommunication systems.
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QUANTUM CRYPTOGRAPHY AND ITS ADVANCES
The reason why the length of quantum cryptology
capability is so short is because of interference. A photon’s
spin can be changed when it bounces off other particles,
and so when it's received, it may no longer be polarized the
way it was originally intended to be.
This means that a 1 may come through as a 0 -- this
is the probability factor at work in quantum physics. As the
distance a photon must travel to carry its binary message is
increased, so, too, is the chance that it will meet other particles
and be influenced by them.
Fig 4.4 Spooky Action Of Photon
SOLUTION DEVELOPED
One group of Austrian researchers may have solved
this problem. This team used what Albert Einstein called
“spooky action at a distance.” This observation of quantum
physics is based on the entanglement of photons. At the
quantum level, photons can come to depend on one another
after undergoing some particle reactions, and their states
become entangled. This entanglement doesn’t mean that the
two photons are physically connected, but they become
connected in a way that physicists still don't understand. In
entangled pairs, each photon has the opposite spin of the other
-- for example, ( / ) and (\ ). If the spin of one is measured, the
spin of the other can be deduced. What’s strange (or “spooky”)
about the entangled pairs is that they remain entangled, even
when they’re separated at a distance.
The Austrian team put a photon from an entangled
Even though it’s existed just a few years so far,
quantum cryptography may have already been cracked. A
group of researchers from Massachusetts Institute of
Technology took advantage of another property of
entanglement. In this form, two states of a single photon
become related, rather than the properties of two separate
photons. By entangling the photons the team intercepted,
they were able to measure one property of the photon and
make an educated guess of what the measurement of
another property -- like its spin -- would be. By not
measuring the photon’s spin, they were able to identify its
direction without affecting it. So the photon traveled down
the line to its intended recipient none the wiser.
pair at each end of a fiber optic cable. When one photon was
measured in one polarization, its entangled counterpart took the
opposite polarization, meaning the polarization the other photon
would take could be predicted. It transmitted its information to
its entangled partner. This could solve the distance problem of
quantum cryptography, since there is now a method to help
predict the actions of entangled photons.
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The
MIT
researchers
admit
that
their
eavesdropping method may not hold up to other systems,
but that with a little more research, it could be perfected.
Hopefully, quantum cryptology will be able to stay one
step ahead as decoding methods continue to advance.
9
QUANTUM CRYPTOGRAPHY AND ITS ADVANCES
POSITION BASED QUANTUM CRYPTOGRAPHY
A central task in position-based cryptography is
Here the study of position-based cryptography in the
the problem of position-verfication. We have a prover P at
quantum setting is investigated. The aim is to use the
position pos, wishing to convince a set of verifiers V0; : : :
geographical position of a party as its only credential. This has
; Vk (at different points in geographical space) that he (i.e.
interesting applications, e.g., it enables two military bases to
the prover) is indeed at that position pos. The prover can
communicate over insecure channels and without having any
run an interactive protocol with the verifiers in order to do
pre-shared key, with the guarantee that only parties within the
this. The main technique for such a protocol is known as
bases learn the content of the conversation.
distance bounding. A verifier sends a random nonce to P
and measures the time taken for P to reply back with this
There are schemes for several important positionbased cryptographic tasks:
position-verification,
value. Assuming that communication is bounded by the
speed of light, this technique gives an upper bound on the
authentication,
and
key
distance of P from the verifier.
exchange, and we prove them unconditionally secure, i.e.,
The set of verifiers cannot distinguish between the case when
without assuming any restriction on the adversaries (beyond
they are interacting with an honest prover at pos and the case when they
the laws of quantum mechanics). Unlike key-distribution,
are interacting with multiple colluding dishonest provers, none of whom
which is possible under cryptographic hardness assumptions
are at position pos. Their impossibility result holds even if we make
alone, position-based cryptography is impossible under any
computational hardness assumptions, and it also rules out most other
hardness assumptions. Thus, this is the first example of a
interesting position-based cryptographic tasks. A model in which verifiers
cryptographic task that we are aware of which is impossible in
can broadcast large bursts of information and there is a bound on the
the standard complexity-based setting but becomes possible
amount of information that the set of adversaries can retrieve. (this model
when using quantum methods. We also present schemes for
is known as the Bounded Retrieval Model (BRM)).
which we can merely conjecture security; proving them secure
(or insecure) remains an interesting challenge.
In
this
model,
constructs
information-
theoretically secure protocols for the task of position
The results open up a fascinating new direction of
verification as well as position-based key exchange
quantum cryptography where security of protocols is solely
(wherein the verifiers, in addition to verifying the position
based on the laws of physics.
claim of a prover, also exchange a secret key with the
prover). The BRM has its drawbacks. Firstly, it requires
The goal of position-based cryptography is to use
the verifiers to be able to broadcast large bursts of
the geographical position of a party as its only “credential”. For
information and this might be difficult to do; secondly, and
example, one would like to send a message to a party at a
perhaps more importantly, the bound on the amount of
geographical position pos with the guarantee that the party can
information that an adversary retrieves might be hard to
decrypt the message only if he or she is physically present at
impose.
pos.
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QUANTUM CRYPTOGRAPHY AND ITS ADVANCES
This work, initiates the study of position-based
classical cryptography and quantum cryptography, in
cryptography in the quantum setting. By going to the
that the latter offers unconditional security whereas the
quantum setting, one may be able to circumvent the
former does not offer any security if the adversary is
impossibility result thanks to the following observation. If
unrestricted.
some information is encoded into a quantum state, then the
It should be stressed that our work exhibits far greater
above attack fails due to the no-cloning principle: the
power of quantum world then what QKD vs. classical key
adversary can either store the quantum state or send it to a
agreement
colluding adversary (or do something in-between, like store
informationtheoretic security, while standard key agreements
part of it), but not both. Thus, going to the quantum setting
provide only computational security. However, one can argue that
may indeed be a promising approach. We put forward
computational security, in some cases, given sufficiently strong
quantum cryptographic schemes for several position-based
cryptographic hardness assumptions is “good enough” and there is
tasks:
no need for more costly quantum implementation.
demonstrates.
In
particular,
QKD
provides
position-verification, authentication, and key
In contrast, position-based key agreement (as well as
exchange, and we prove these scheme unconditionally
other position-based cryptographic tasks) are provably impossible
secure against an arbitrary coalition of adversaries.
to achieve in the classical cryptographic setting, even if we
As already mentioned, a position-verification
scheme can be used to convince the verifiers V0; : : : ; Vk
assume that P is different from NP and there are cryptographically
hard problems that are provably impossible to break.
of the geographic position pos of P. A position-based
This demonstrates an existence of a task that is
authentication scheme on the other hand convinces the
impossible in the classical setting and is readily realizable
verifiers that a message m originates from P at position pos.
using quantum communication. An additional attractive
Finally, a position-based key exchange scheme ensures that
feature of all our solutions is that our schemes merely
the verifiers share a secret key with P at position pos, and
require one of the verifiers, V0, to prepare individual
anyone that is not at position pos does not have any
qubits and send them to P, and P needs to measure them
information regarding the key.
immediately upon arrival.
If this is possible, and the key is sufficiently
long, then perfectly secure communication with a device
No quantum computation is needed, and all
other communication may be classical.
only located in a certain position is possible.
This scheme prove security for the above tasks
Classical cryptographic protocols in a quantum world
without any restriction on the power of the adversaries; they
may have unbounded classical and quantum memory, and
Our main contribution is showing the existence
they may have unbounded computing power; the only
of classical two-party protocols for the secure evaluation
assumption is that the laws of quantum mechanics hold.
(SFE) of any polynomial-time function that are secure
Therefore, our results show that position-based
against quantum attacks under reasonable computational
quantum cryptography is one of the rare examples besides
assumptions (for example, it suffices that the learning with
QKD for which there is a strong separation between
errors problem be hard for quantum polynomial time).
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QUANTUM CRYPTOGRAPHY AND ITS ADVANCES
We show that a large class of classical security
The need to secure our data is the prime aim of most
analyses remain valid in the presence of quantum attackers as
firms.One of the most advanced techniques used for solving this
long as the underlying computational primitives (encryption
issue is ‘cryptology’. Cryptology means the encoding of our
schemes, pseudorandom generators, etc) resist quantum attack.
sensitive information into forms unrecognizable by others. But
In what follows, we distinguish two basic settings: in the stand-
traditional cryptology methods have a lot of flaws. And that is
alone setting, protocols are designed to be run in isolation,
where the necessity of Quantum Cryptology lies.
without other protocols running simultaneously; in network
It is very important that potential intruders (and their
settings, the protocols must remain secure even when the
corresponding activities) are taken into consideration before
honest participants are running many other protocols (or copies
devising a security system. This is exactly what Quantum
of the same protocol) concurrently. Protocols that are secure in
Cryptology helps in.
arbitrary network settings are called universally composable.
Photons being the keys of transmission can be highly
unpredictable by a third party. By observing the spin of these
Modeling stand-alone security with quantum adversaries:
photons interception by unauthorized parties can be detected. This
We describe a security model for two party
makes Quantum Cryptology one of the most efficient means of
protocols in the presence of a quantum attackers. Proving
‘hiding’ data. Another feature of Quantum Cryptology is that it is
security in this model amounts to showing that a protocol for
purely physics, while all the other present cryptography
computing a function f behaves indistinguishably from an
techniques are based on mathematics.
“ideal” protocol in which of is computed by a trusted third
Current computers will be replaced in the near future
party. Our model captures both classical and quantum
with quantum computers, which exploit the properties of physics
protocols, though we only apply it to classical ones. The new
on the immensely small quantum scale. Since they can operate on
model is significantly more general than existing stand-alone
the quantum level, these computers are expected to be able to
models of security. This allows us to design protocols
perform calculations and operate at speeds no computer in use
assuming that all participants share a uniformly random
now could possibly achieve. So the codes that would take a trillion
common reference string (CRS). By the modular composition
years to break with conventional computers could possibly be
theorem, we can then use the DL coin-flipping protocol to
cracked in much less time with quantum computers.
generate the CRS.
Hopefully these computers will be able to
increase the speed of decoding into just minutes and
thus make cryptography worthwhile and encourage the
CONCLUSIONS AND FUTURE WORKS
widespread use of cryptology in everyday life.
Position Based Quantum Cryptology is
In this computer-centric era, the relevance of
security systems have increased to great heights. Though
present day security systems offer a good level of
protection, they are incapable of providing a “trustworthy”
technique being developed to enhance the present
quantum cryptography scenario. It is based on sending
confidential encoded data to a specific person seated in
a specific position of geographical earth. This ensures
environment and are vulnerable to unexpected attacks or
third party interception.
Sahrdaya College Of Engineering and Technology
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QUANTUM CRYPTOGRAPHY AND ITS ADVANCES
“Position-based quantum cryptography,”
that our secure data does not fall into wrong hands. It
avoids possible interceptions and unauthorized access.
2010, (full version), ArXiv eprints/
Presently, cryptography is used only by the
1005.1750.
higher level authorities such as in government affairs and
military. Soon, it could reach down to the common man,
helping
him
secure
his
data
from
intruders
[9]
N.
Chandran,
B.
Kanukurthi,
R.
Ostrovsky, and L. Reyzin, “Privacy
and
amplification with asymptotically optimal
entropy loss,” in STOC’10.
eavesdroppers.
New York: ACM Press, 2010, pp. 785–
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[1] Proceedings of the International Conference
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