40
votes
Accepted
What makes Quantum Cryptography secure?
TL;DR The answer is classical cryptography.
Besides a quantum link, secure data communication with Quantum Cryptography (more precisely, Quantum Key Distribution) uses classical links, ...
- 146k
10
votes
What makes Quantum Cryptography secure?
@fgrieu already wrote a little book, so I'll restrict my answer to a minimum to avoid repetitions. Think of this as an extended comment (which indeed wouldn't have fit the comment size limits).
What ...
- 18.1k
7
votes
What makes Quantum Cryptography secure?
My turn!
In classical cryptography between two peers over a channel such as the internet, an eavesdropper on the channel learns a transcript of information from which secrets could theoretically be ...
- 49.5k
6
votes
Is E91 safer than BBM92?
The answer is both yes and no, as I explain below.
1. No, BBM92 is better (or at least, we initially thought so)
E91 was the initial idea which led to the more rigorous BBM92.
In the E91 paper, there ...
5
votes
What makes Quantum Cryptography secure?
There is some confusion regarding QKD. The confusion revolves around the underlying principle and it's nuts & bolts implementation in the physical world. The two are conflated, which I believe ...
- 15.7k
5
votes
Why in one time pad must the key distribution to be truly random
For an OTP to provide perfect secrecy it is required that the key stream is indeed purely random. A pure OTP is largely a theoretical construct because it is almost impossible to generate a key stream ...
- 94.5k
5
votes
Understanding Quantum Key Distribution
How Alice and Bob agree on which of the two beam splitters bases (Horizontal-Vertical and Right-Left) correspond to which of the classical bits (1 and 0) ? How do Alice and Bob agree on when actual ...
- 146k
4
votes
Accepted
Why is this voting system not secure?
Unfortunately, most of the reasons that e-voting is not popular have nothing to do with the integrity of the underlying mathematics. This makes the question slight moot on a cryptography forum, but ...
- 15.7k
4
votes
Accepted
Does an EC signature preserve entropy?
Ed25519 is a typical elliptic-curve signature scheme, in a group of large prime order $\ell \approx 2^{252}$ on a curve over the field $\mathbb F_p$ for $p = 2^{255} - 19$. A secret key is a uniform ...
- 49.5k
4
votes
Key Exchange & key Distribution in symmetric key cryptography
I think the difference between key exchange and key distribution can be very subtle, but it probably comes down to the former being an active way of "dealing" keys, while the latter is something that ...
- 2,480
3
votes
Centered Binomial Distribution vs Fixed Weight Ternary Sampler
There are a couple of misconceptions here.
Firstly, the a Centred Binomial Distribution with $\eta=1$ has expected Hamming density 0.5. In particular, it is possible (although unlikely) that the CBD ...
- 26.4k
3
votes
Accepted
Multi party anonymous key distribution
OpenPGP supports an approximation to what you seek, albeit with at best weak privacy guarantees: To transmit the message $m$, Alice picks a session key $k$ and sends $$E_{f_1}(k) \mathbin\| E_{f_2}(k) ...
- 49.5k
3
votes
One Time Pad Key Distribution
This principle is commonplace, it is a key derivation from a shared secret. The academic thing to do is to use a Key Derivation Function or a MAC where hash of a concatenation is used, perhaps
$$\...
- 146k
3
votes
Struggling to understand Perfect Forward Secrecy
But I read a question here that PFS can be achieved by deriving session keys with a hash of an old session key. But if I were to know the master key (the pre-shared key?), I could easily calculate all ...
- 46.4k
2
votes
Why Nonces and timestamps are used in Public key authority?
To understand how nonces and timestamps are used to prevent a replay attack, you must understand generally what a replay attack is. A replay attack is a network attack in which a data transmission (...
2
votes
Protocol that generates keys every 2 minutes using KDC
Look into the Signal protocol and its associated Double Ratchet algorithm. This changes DH keys after every message without much overhead. As no prime generation is involved in generating new DH keys, ...
- 15.5k
2
votes
One Time Pad Key Distribution
We call this idea a key derivation function (hashing the ECDH secret) for a stream cipher (expanding a short secret and a counter into a long pad).
This idea is not problematic or weak; in fact, it ...
- 49.5k
2
votes
Accepted
Why is it difficult to encrypt large amounts of information using quantum key distribution?
I believe the end goal is to use the QKD data as a one-time pad, so the QKD rate would need to be the same as the plaintext data rate. That is the only guaranteed-secure method. (Although I think ...
- 124
1
vote
How to redistribute shares for Distributed Shamir Secret Sharing?
Why do you want to refresh the shares? Why can't you simply do a new DKG altogether with the updated parameters & distribute the new shares to the participants?
- 11
1
vote
How to generate Multiple Encryption Keys for use in RSA polymorphic multiplication
Besides the answer Dimitree gave to himself, I' like to add something even if I am not sure whether I understand the original problem he wanted to solve.
You used the same message a and encrypted it ...
- 51
1
vote
Why is it difficult to encrypt large amounts of information using quantum key distribution?
The breakthrough in the article is a little misleading. As you correctly stated it's possible to send an (almost) unlimited amount of encrypted data using a symmetric encryption algorithm like AES. ...
- 6,511
1
vote
Why in one time pad must the key distribution to be truly random
Most of it is by definition, use a key twice, or use a pseudo random number as the key, its no longer a one time pad (because that's not how its defined).
Why would an encryption technique be weaker ...
- 912
1
vote
Number of uniform n-bit strings
This is a problem of permutations with repetition, as we have repeated 1s and 0s. The general formula is quite simple:
$$
P_r=\frac{n!}{n_0!n_1!...n_k!}
$$
$n$ is the number of objects (the length of ...
- 11
1
vote
Dividing a secret into multiple nodes in a blockchain kind of system with time-release?
I understand what you are thinking, but you are mixing concepts. Just try to put the public parts of your schema at the blockchain... For instance, if you want to implement a PKI scheme without ...
- 11
1
vote
What are the current known weaknesses/attacks on quantum key distribution?
The Attack you mentioned (PNS) is a "hardware attack" it depends on how you physically distribute the qubits.
The only "protocol attack" (known for the BB84) is the "intercept & resend" that can ...
1
vote
How are one-time pads distributed?
Use a trusted messenger. If possible, transfer the OTP yourself.
Sending OTP keys over the Internet is usually not a very good idea because "the distribution itself won't deliver perfect security" ...
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