Device-Independent Quantum Key Distribution: Difference between revisions

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A device-independent quantum key distribution protocol implements the task of [[Quantum Key Distribution]] (QKD) without relying on any particular description of the underlying system. The protocol enables two parties, Sender and Receiver, to establish a classical secret key by distributing an entangled quantum state and checking for the violation of a [[Bell inequality]] in order to certify the security. The output of the protocol is a classical secret key which is completely unknown to any third party, namely an eavesdropper.  
A device-independent quantum key distribution protocol implements the task of [[Quantum Key Distribution]] (QKD) without relying on any particular description of the underlying system. The protocol enables two parties, Alice and Bob, to establish a classical secret key by distributing an entangled quantum state and checking for the violation of a [[Bell inequality]] in order to certify the security. The output of the protocol is a classical secret key which is completely unknown to any third party, namely an eavesdropper.  


'''Tags:''' [[:Category:Two Party Protocols|Two Party]], [[:Category:Quantum Enhanced Classical Functionality|Quantum Enhanced Classical Functionality]], [[:Category:Specific Task|Specific Task]],[[Quantum Key Distribution]], [[BB84 Quantum Key Distribution|BB84 QKD]], [[Category:Multi Party Protocols]] [[Category:Quantum Enhanced Classical Functionality]][[Category:Specific Task]][[Category:Entanglement Distribution Network Stage]]
'''Tags:''' [[:Category:Two Party Protocols|Two Party]], [[:Category:Quantum Enhanced Classical Functionality|Quantum Enhanced Classical Functionality]], [[:Category:Specific Task|Specific Task]],[[Quantum Key Distribution]], [[BB84 Quantum Key Distribution|BB84 QKD]], [[Category:Multi Party Protocols]] [[Category:Quantum Enhanced Classical Functionality]][[Category:Specific Task]][[Category:Entanglement Distribution Network Stage]]
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==Outline==
==Outline==
A DIQKD protocol is composed by the following steps:
A DIQKD protocol is composed by the following steps:
*'''Distribution:''' For each round of the distribution phase:
* The first phase of the protocol is the distribution. For each round of this phase:
** Sender uses the source to prepare a maximally entangled state and send half of the state to Receiver.
** Alice uses the source to prepare a maximally entangled state and send half of the state to Bob.
** Upon receiving the state, Receiver announces that he received it, and they both use their respective devices to measure the quantum systems. They record their output in a string of bits.
** Upon receiving the state, Bob announces that he received it, and they both use their respective devices to measure the quantum systems. They record their output in a string of bits.
A second phase where Sender and Receiver publicly exchange classical information in order to perform [[error correction]], where they correct their strings generating the raw keys, and [[parameter estimation]], where they estimate the parameters of interest. At the end of this phase Sender and Receiver are supposed to share the same <math>n</math>-bit string and have an estimate of how much knowledge an eavesdropper might have about their raw key.
The second phase is when Alice and Bob publicly exchange classical information in order to perform [[error correction]], where they correct their strings generating the raw keys, and [[parameter estimation]], where they estimate the parameters of interest. At the end of this phase Alice and Bob are supposed to share the same <math>n</math>-bit string and have an estimate of how much knowledge an eavesdropper might have about their raw key.
* In the final phase, Sender and Receiver perform [[privacy amplification]], where the not fully secure <math>n</math>-bit strings are mapped into smaller strings <math>K_A</math> and <math>K_B</math>, which represents the final keys of Sender and Receiver respectively.
* In the final phase, Alice and Bob perform [[privacy amplification]], where the not fully secure <math>n</math>-bit strings are mapped into smaller strings <math>K_A</math> and <math>K_B</math>, which represents the final keys of Alice and Bob respectively.


==Hardware Requirements ==
==Hardware Requirements ==
*'''Network Stage:''' [[:Category: Entanglement Distribution Network Stage|Entanglement Distribution]]
*'''Network Stage:''' [[:Category: Entanglement Distribution Network Stage|Entanglement Distribution]]
*'''Relevant Network Parameters:''' <math>\epsilon_T, \epsilon_M</math> (see [[:Category: Entanglement Distribution Network Stage|Entanglement Distribution]])
*'''Relevant Network Parameters:''' <math>\epsilon_T, \epsilon_M</math> (see [[:Category: Entanglement Distribution Network Stage|Entanglement Distribution]])
* Distribution of Bell pairs, and measurement in three different bases (two basis on Sender's side and three basis on Receiver's side).
* Distribution of Bell pairs, and measurement in three different bases (two basis on Alice's side and three basis on Bob's side).
* Minimum number of rounds ranging from <math>\mathcal{O}(10^6)</math> to <math>\mathcal{O}(10^{12})</math> depending on the network parameters, for commonly used secure parameters.
* Minimum number of rounds ranging from <math>\mathcal{O}(10^6)</math> to <math>\mathcal{O}(10^{12})</math> depending on the network parameters, for commonly used secure parameters.
* <math>QBER \leq 0.071</math>, taking a depolarizing model as benchmark. Parameters satisfying <math>\epsilon_T+\epsilon_M\leq 0.071</math> are sufficient.
* <math>QBER \leq 0.071</math>, taking a depolarizing model as benchmark. Parameters satisfying <math>\epsilon_T+\epsilon_M\leq 0.071</math> are sufficient.
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* [[Random number generator]].
* [[Random number generator]].


==Notations Used==
==Notation==
* <math>n</math> expected number of rounds
* <math>n</math> expected number of rounds
* <math>l</math> final key length  
* <math>l</math> final key length  
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*<math>\nu_1=2 \Big(\log 7 +\left\lceil\frac{|h'(\omega_{exp}+\delta_{est})|}{1-(1-\gamma)^{s_{\max}}}\right\rceil\Big)\sqrt{1-2\log\epsilon_s}</math>
*<math>\nu_1=2 \Big(\log 7 +\left\lceil\frac{|h'(\omega_{exp}+\delta_{est})|}{1-(1-\gamma)^{s_{\max}}}\right\rceil\Big)\sqrt{1-2\log\epsilon_s}</math>


==Pseudo Code==
==Pseudocode==
*'''Input:'''<math>n, \delta</math></br>
*'''Input:'''<math>n, \delta</math></br>
*'''Output:'''<math>K_A, K_B</math></br>
*'''Output:'''<math>K_A, K_B</math></br>
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##'''While''' <math>i \leq s_{max}</math>
##'''While''' <math>i \leq s_{max}</math>
###Set <math>i=i+1</math>
###Set <math>i=i+1</math>
### Sender and Receiver choose a random bit <math>T_i \in \{0,1\}</math> such that <math>P(T_i=1)=\gamma</math>.
### Alice and Bob choose a random bit <math>T_i \in \{0,1\}</math> such that <math>P(T_i=1)=\gamma</math>.
### '''If''' <math>T_i=0</math> '''then''' Alice and Bob choose inputs <math>(X_i, Y_i)=(0,2)</math>.  
### '''If''' <math>T_i=0</math> '''then''' Alice and Bob choose inputs <math>(X_i, Y_i)=(0,2)</math>.  
### '''Else''' they choose  <math>X_i ,Y_i \in \{0,1\}</math>  (the observables for the CHSH test).
### '''Else''' they choose  <math>X_i ,Y_i \in \{0,1\}</math>  (the observables for the CHSH test).
### Sender and Receiver use their devices with the respective inputs and record their outputs, <math>A_i</math> and <math>B_i</math> respectively.
### Alice and Bob use their devices with the respective inputs and record their outputs, <math>A_i</math> and <math>B_i</math> respectively.
### '''If''' <math>T_i=1</math> they  set <math>i=s_{max}+1</math>.
### '''If''' <math>T_i=1</math> they  set <math>i=s_{max}+1</math>.
*At this stage Sender holds strings <math>X_1^n, A_1^n</math> and Receiver <math>Y_1^n, B_1^n</math>, all of length <math>n</math>.
*At this stage Alice holds strings <math>X_1^n, A_1^n</math> and Bob <math>Y_1^n, B_1^n</math>, all of length <math>n</math>.


<u>'''Stage 2'''</u> Error Correction</br>
<u>'''Stage 2'''</u> Error Correction</br>
* Sender and Receiver apply the error correction protocol <math>EC</math>, communicating script <math>O_{EC}</math> in the process.  
* Alice and Bob apply the error correction protocol <math>EC</math>, communicating script <math>O_{EC}</math> in the process.  
# '''If''' <math>EC</math> aborts, they abort the protocol
# '''If''' <math>EC</math> aborts, they abort the protocol
# '''Else''' they obtain raw keys <math>\tilde{A}_1^n</math> and <math>\tilde{B}_1^n</math>.
# '''Else''' they obtain raw keys <math>\tilde{A}_1^n</math> and <math>\tilde{B}_1^n</math>.
<u>'''Stage 3'''</u> Parameter estimation</br>
<u>'''Stage 3'''</u> Parameter estimation</br>
#Using <math>B_1^n</math> and <math>\tilde{B}_1^n</math>, Receiver sets <math>C_i</math>
#Using <math>B_1^n</math> and <math>\tilde{B}_1^n</math>, Bob sets <math>C_i</math>
##'''If''' <math>T_i=1</math>  and <math>A_i\oplus B_i=X_i\cdot Y_i</math> '''then''' <math>C_i=1</math>  
##'''If''' <math>T_i=1</math>  and <math>A_i\oplus B_i=X_i\cdot Y_i</math> '''then''' <math>C_i=1</math>  
##'''If''' <math>T_i=1</math>  and <math>A_i\oplus B_i=X_i\cdot Y_i</math> '''then''' <math>C_i=0</math>
##'''If''' <math>T_i=1</math>  and <math>A_i\oplus B_i=X_i\cdot Y_i</math> '''then''' <math>C_i=0</math>
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<u>'''Stage 4'''</u> Privacy amplification</br>
<u>'''Stage 4'''</u> Privacy amplification</br>
*<math>PA(\cdot,\cdot)</math> is a privacy amplification subroutine
*<math>PA(\cdot,\cdot)</math> is a privacy amplification subroutine
# Sender and Receiver run <math>PA(A_1^{n'},\tilde{B}_1^{n'})</math> and obtain secret keys <math>K_A, K_B</math>;
# Alice and Bob run <math>PA(A_1^{n'},\tilde{B}_1^{n'})</math> and obtain secret keys <math>K_A, K_B</math>;


==Further Information==
==Further Information==


<div style='text-align: right;'>''*contributed by Bas Dirke, Victoria Lipinska, Glaucia Murta and Jeremy Ribeiro''</div>
<div style='text-align: right;'>''contributed by Gláucia Murta''</div>
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