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Questions tagged [bb84]

For questions related to quantum cryptography protocol BB84.

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2 votes
1 answer
40 views

How to show that BB84 is safe against imperfect cloning?

One of the reasons why BB84 is usually considered safe is due to the no-cloning principle. However, as far as I know imperfect cloning of quantum states is possible. I've been thinking about a ...
3 votes
2 answers
387 views

Can weak measurements or quantum state tomography break bb84?

I am currently reading through this paper and read some of the wikipedia pages on weak measurement and quantum tomography and I am curious if weak measurement could be used to break BB84 quantum key ...
1 vote
0 answers
50 views

Doubt in Shor-Preskill's proof of security proof of BB84

I was going through the proof of security of the modified Lo-Chau protocol, which eventually leads to the proof of security of BB84. In the error correction step, Nielson-Chuang mention that any ...
2 votes
1 answer
150 views

Doubt in understanding the use of Uhlmann's Theorem in BB84 security proof

I was going through the security proof of the BB84 protocol by Dr. Ramona Wolf. I am having trouble following the equation (used at 8:53) for the fidelity, \begin{align*} F(\rho_{ABE},\left|\phi\right\...
3 votes
0 answers
61 views

Mutual information between Alice and Eve in a BB84 intercept resend attack

I'm new to information theory and i need to calculate $I(A,E)$. To calculate it I need conditional entropy $H(A|E)$. I assume the BB84 protocol standard states $\{ |0\rangle,|1\rangle \},\{|+\rangle,|-...
2 votes
1 answer
95 views

Security of BB84 QKD protocol

I am studying the BB84 protocol and I have some doubts regarding its security. Consider the following example: Alice wants to send a message to Bob over a public quantum channel, where a third person (...
5 votes
1 answer
296 views

Is the BB84 protocol an example of "quantum supremacy"?

This is a fairly broad question, I hope it fits here. I am wondering if the BB84 protocol is an example of "quantum supremacy", ie. something a quantum computer can do but something that is assumed a ...
3 votes
0 answers
337 views

Entangling attack on BB84 protocol

I am trying to solve the exercise 5.3 from the book "A Gentle Introduction to Quantum Computing". The exercise reads as follows: Suppose Eve attacks the BB84 quantum key distribution of ...
3 votes
1 answer
49 views

How to correctly describe state preparation?

I came across a rather basic state-preperation description that I didn't fully understand. So far, I thought I got the basics of density matrices, but now I am confused. I hope you can help me finding ...
9 votes
1 answer
530 views

What authentication protocol to use for BB84 and other QKD protocols?

Just like other classical and quantum key distribution protocols, BB84 is vulnerable to "man"-in-the-middle attacks, where Eve pretends to be Bob to Alice, and Eve pretends to be Alice to ...
1 vote
0 answers
85 views

Can quantum teleportation be used to break BB84?

BB84 is a key quantum distribution scheme, which is supposed to be "provably secure" and resistant to an individual eavesdropper. However, from what I can tell, is seems as if one could ...
2 votes
1 answer
110 views

How can entanglement deal with individual attack in QKD?

Based on a photon source, Alice shares with Bob set of photon pulse. But we know that the probability that after a pulse single photon is generated is very small, each pulse will always contain many ...
1 vote
1 answer
602 views

Number of qubits in quantum circuits in ibm qiskit

How to find number of Qubits ? ...
2 votes
1 answer
99 views

Choosing E91/BB84 basis states and angles

What is the logic for choosing the angles of E91 for the specific basis states? I have noticed a variety of different angles being used as the basis states for Alice and Bob. Would adding more basis ...
0 votes
1 answer
84 views

Misunderstanding of QKD BB84 protocol

I am studying the BB84 protocol and I think I have a slight misunderstanding. As far as I understand, if Bob measures the photon in the same basis as it was prepared by Alice, he is going to receive ...
2 votes
1 answer
155 views

How does a rectilinear filter used for QKD-BB84 detect both horizontal and vertical polarizations?

When using the BB84 algorithm for QKD, you arbitrarily choose which of two filters (bases) to use when detecting a photon: rectilinear or diagonal. If you choose rectilinear, you can detect ...
1 vote
1 answer
71 views

Derivations of Equations (12.205 - 12.207) in Nielsen Chuang

While proving the security of the BB84 protocol, Nielsen and Chuang demonstrate that it is possible to reduce the CSS protocol to the secure BB84 protocol without requiring Alice to reveal the value ...
1 vote
0 answers
56 views

What do we mean by family of CSS codes?

In proving the security of BB84 in Nielsen and Chuang (10th anniversary edition - Section 12.6.5), they argue that a codeword in $\text{CSS}(C_1, C_2)$ is represented by $$\frac{1}{\sqrt{|C_2|}} \sum\...
3 votes
1 answer
76 views

Why is applying a Hadamard transform useful in the entanglement-based version of BB84

In Simple Proof of Security of the BB84 Quantum Key Distribution Protocol, the description of the entanglement-based version of BB84 indicates that Alice and Bob perform a Hadamard transform on their ...
4 votes
0 answers
148 views

Probability of error in BB84 if Eve is using Breidbart's basis

I'm taking a course on quantum cryptography and I have a homework to calculate probability of error in BB84. The task says to assume that Eve uses the Breidbart basis with eigenvectors $$|φ_0⟩ = \cos(...
4 votes
0 answers
125 views

Is there a BB84 "man"-in-the-middle attack forcing the same keys on Alice and Bob known to Eve

Consider the following scenario: Alice and Bob run BB84 to each other. Eavesdropper Eve is present in the middle. Here we assume that she has access to all channels: the quantum channel, in the ...
1 vote
1 answer
57 views

Formal measurement of the probability of an outcome of a Qubit in the hadamard base

I am fairly new to Quantum Computing and have a question which might be trivial for all of you, but I am really struggling with it. From Quantum Computation and Quantum Information I have learned, ...
2 votes
1 answer
46 views

Where can I find a detailled exposition of the Information theoretic part of BB84?

I understand the general idea of information reconciliation and advantage distillation, but I can't find any exposition of the algorithm used, unlike the quantum part of the protocol which is well ...
4 votes
1 answer
709 views

Eavesdropping in case of the BB84 Protocol

I try to understand eavesdropping in case of the BB84 protocol (lets assume we have single photons, no noise etc.). Alice and Bob generate a classical random bit $a_i'$ and $b_i'$. Alice generates an ...
1 vote
1 answer
261 views

Heisenberg Uncertainty Principle for BB84 Protocol using Paulis Spin Matrices

I am doing a term project on the BB84 Protocol and it makes use of the Heisenberg Uncertainty Principle. I think I understand the principle in theory. If we have two non-commuting observables, then we ...
0 votes
1 answer
115 views

BB84 Protocol doubt

I was studying BB84 protocol from lecture notes by John Watrous. I had some doubts which i thought of asking. Here is the protocol. Alice prepares strings $x=(01110100)$ and $y=(11010001)$. based on ...
1 vote
1 answer
258 views

Comprehension questions on quantum cryptography especially BB84

I have recently read a lot about the BB84 protocol, I have used three primary sources, the original work, a QK book, and a diploma thesis. My questions refer to the photons sent by Alice, the base of ...
4 votes
1 answer
484 views

Show That an Intercept and Resend Attack on all qubits reduces mutual information

Exercise 5.3.3 With no eavesdropping the mutual information $H(A:B)$ between the substring of $\mathcal R$ held by Alice and $\mathcal R'$ held by Bob is $1$ bit. Show that if Eve is performing an ...
3 votes
1 answer
87 views

Doubt in CSS error correction step

At the end of page 3 in Simple proof of security of the BB84 QKD, the following equation (equation 4) is given : $$ \begin{array}{r} \frac{1}{2^{n}\left|C_{2}\right|} \sum_{z}\left[\sum_{w_{1}, w_{2} ...
3 votes
1 answer
233 views

Doubt in Simple proof of Security of the BB84 QKD

I am not able to understand an argument from Simple proof of Security of the BB84 QKD; I need your help. In page 2 it is mentioned that "Alice can measure her half of the encoded EPR pairs before ...
5 votes
3 answers
926 views

How are eavesdroppers detected when using BB84 in the presence of noise?

I would like to expand upon this question: What is the probability of detecting Eve's tampering, in BB84? Let's say that when the receiver (colloquially referred to as Bob) receives a qubit and ...
1 vote
2 answers
119 views

Show when $a_k$ and $b_k$ are correlated when measuring in different bases, in the BB84 protocol

I'm trying to answer the following question about the BB84 protocol from Nielsen and Chuang's Introduction to Quantum Information. As I understand it, the string $b$ is determining whether we are ...
3 votes
1 answer
139 views

Counting channel uses of the lossy bosonic channel or definition of channel uses

The PLOB-bound ("Fundamental Limits of Repeaterless Quantum Communications") gives an asymptotic upper bound on the secret-key rate per used lossy bosonic channel. However, I'm not sure how to count ...
1 vote
1 answer
984 views

What is the probability of detecting Eve's tampering, in BB84?

Alice sends a 0 in computational basis I understand that theres a $\frac12$ probability that eve guesses the basis wrong, and can go with Hadamard. So it's $\frac12$ chance Eve will pick computational ...
11 votes
1 answer
2k views

How many bits do Alice and Bob needs to compare to make sure the channel is secure in BB84?

I was trying to self-study qmc by reading the Quantum Computing A Gentle Introduction book, in section 2.4 it talks about the quantum key distribution protocol BB84. After (I thought) I understood it ...
1 vote
1 answer
236 views

How to deal with noise in BB84 protocol?

BB84 protocol works followingly: Alice generate $N$ random qubits $a_i$ in state either $|0\rangle$ or $|1\rangle$ . These will be a key. Then she prepares $N$ random bits $b_{i}$. If $b_i=0$, an ...
5 votes
1 answer
313 views

In the BB84 protocol, for what error thresholds can Alice and Bob not establish secure bits?

Suppose Alice and Bob can communicate over a quantum channel. The quantum channel is noiseless in the absence of eavesdropping, a condition that cannot be guaranteed. They can also communicate over a ...
4 votes
1 answer
125 views

Does the Lieb-Robinson bound constrain the speed of entanglement information transmission?

I just learned from the existence of the theoretical Lieb-Robinson bound, which indicates that the speed at which information can be propagated in non-relativistic quantum systems cannot exceed this ...
2 votes
1 answer
88 views

Show that if $b'$ and $b$ are uncorrelated, then $a'$ and $a$ are uncorrelated

Let $a'_k$ be Bob's measurement result of qubit $ {\Psi_{a_kb_k}}$, assuming a noiseless channel with no eavesdropping. Show that when $b'_k\neq b_k$, $a'_k$ is random and completely uncorrelated ...
0 votes
1 answer
151 views

What is the quantum state transmitted to Bob in BB84 protocol?

Sender (Alice) wants to exchange private encryption key with Bob using BB84 protocol. She generate a binary string (1010100010010111),and encode using Hadamard gate and identity gate (HHHIIHIHHIIIHIIH)...
2 votes
1 answer
78 views

Any good resources for learning about quantum networks and how to do a simulation of BB84 protocol?

I'm a communication engineering student. And I'm thinking of doing my project on BB84 protocol but I don't know where to start. As a beginner, are there any documents or tutorials about quantum ...
0 votes
1 answer
128 views

Is it a good idea to publish a research paper about the simulation of BB84 protocol?

I'm an engineering student. As my end of year project I've simulated BB84 protocol using simulaqron(python). I'm thinking about publishing a paper about this simulation. I haven't published any ...
3 votes
1 answer
499 views

Can Eve randomly guess the correct bases in the BB84 exchange of a one-time pad?

I'm learning about Quantum Key Distribution, and just learned about the BB84 exchange. I learned that it can be used to exchange a key for a one-time pad, which would allow for information-...
0 votes
2 answers
86 views

Is there a notion of “computational security” in quantum cryptography?

In classical cryptography, security proofs are often based on the (assumed) computational hardness of some mathematical problem. Using the principles of quantum mechanics might provide means to design ...
2 votes
1 answer
232 views

Hadamard gate with two inputs in the circuit for the BB84 protocol?

I am reading the book "Quantum Computing verstehen" by Matthias Homeister. At the moment i'm having a look at the BB84 protocol (which is described in kind of an abstract way). In this chapter a ...
1 vote
0 answers
94 views

Why Alice and Bob don't get the same result when they measure in the same basis?

I'm simulating the BB84 protocol using simulaqron. My problem is that when Alice and Bob measure in the same basis, they don't get the same result. How can I fix this error? . BB84.py ...