Latest Crypto related questions

Score: 0
arsenne lupulupin avatar
Get bit i when modulo n
jo flag

Is there a way to recover the bit sequence of a number ( for example 29 = 0b11101 ) by always dividing it by 2 when in mod 143 for example ?

What I mean by that is recover the number bit by bit by multiplying it by the inverse of 2 mod 143 to simulate the /2 division. for example:
$\begin{array}{} &29\bmod143=&29&\equiv 1 \pmod 2\\ 29\cdot(2^{-1}\bmod143)^1\bmod143=&29\cdot72^1\bmod143= ...

Score: 2
Manglemix avatar
Is this a safe zero knowledge proof that two paillier encryptions are equal?
us flag

We have encryptions $c_1$ and $c_2$, the person who knows the plaintext and randomness in both wants to prove that they know it. Let $r_1$ and $r_2$ be the randomness values in $c_1$ and $c_2$ respectively. The prover then randomly generates another random number, $z$. They then calculate $a_1 = r_1^n z^n$, $a_2 = r_2^n z^n$. These are the proofs. A verifier would just have to multiply $a_2$ with

Score: 0
Zero-knowledge proofs for preventing data abuse
es flag

I am looking for a theoretical solution to the following problem: Alice receives a signed statement from her bank with information about her account and credit balance. Alice wants to prove this knowledge of the contents and the bank's valid signature to Bob, but at the same time prevent Carol from determining who signed the proof.

To better illustrate my problem, I took the liberty of making a s ...

Score: 0
Baldovín Cadena Mejía avatar
What's the difference between permutation and transposition?
cn flag

I am trying to understand the difference between permutation and transposition. I have seen a similar question in the forum but I would like to ask you for proper definitions and examples of each. I'm trying to understand the DES algorithm and I'd like to understand if the halving of the initial block and eventual swapping of the halves would be permutation or transposition. Thank you in advance.

 ...
Score: 0
Cryptography (DSA) Get Value of k and private Key
ng flag

i am on a task in cryptography and need a hint (PLEASE NO SOLUTION).

The Task is:

I can send Messages (Digital Numbers) to a Docker Container. The response are the values p,q,g,z1,s,r and hashvalue(m+z1). So... when i enter the number 1 i get the DSA values used for signing.

Unknown is the value of k, z2 and x (the private key)

Known is that p,q,g,z1,z2 are fixed for every message. So they are the same ev ...

Score: 0
Manglemix avatar
In paillier homomorphism, how is the randomness r changed during addition?
us flag

Two add the plaintexts encrypted in a ciphertext, you would just multiply the ciphertext and modulo it. However, how does the randomness value of the new ciphertext change? Assuming you the encryptor knew the randomness values in both ciphertexts, could you calculate the new randomness value?

Score: 0
Shweta Aggrawal avatar
Are there applications of sanitizable signatures without transparency property?
us flag

Are there applications of sanitizable signatures without transparency property ?

Score: 0
Dominic Teplicky avatar
Why is this image not pre-image resistant?
ar flag

enter image description here

The answers to my HW say that a preimage of a single block is easily found. I do not understand how it is easily found. Please help.

Score: 0
Hedeesa avatar
Understanding MITM in an example authentication protocol
de flag

Imagine that we have a protocol like this:
B -> A: RB
A -> B: {RB,B}K

Goal: authenticate A to B
K: a shared key between A and B
{}K: encrypting by K

After receiving {RB, B}K by B, B is able to authenticate A. But what if we have something like:
A -> C: {RB,B}K
C -> B: {RB,B}K
so in this case B will authenticate C instead of A, isn't it?

Score: -1
How to decrypt a file using RSA and just a public.pem file?
in flag

I have an encoded file and a public.pem file. Is it possible to decode the file using the public.pem file or do I have to start looking at private keys?

I tried https://github.com/Ganapati/RsaCtfTool with no luck. The public key (pem) is as below

-----BEGIN PUBLIC KEY-----
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAjHDiqVkO1umD2/Tm20Wt
LpyBXGoIk4Pczeqjwz7/kwYLnQI7VlAzgjC9jD1dX80Z+kLOr5wHIDdfNK55 ...
Score: 1
Proof that exchanged variable was not modified with MITM
es flag

If I understand correctly, the core of man in the middle attack is in being able to replace an exchanged variable (public key) with another.

Hence to detect a MITM one needs to check if the exchanged public key is truly same for both A and B, and to defend against MITM one needs to be able to exchange a variable without it being modified.

I'd imagine it should be possible to detect a change in varia ...

Score: 0
SHA-256 doesn't follow a uniform distribution?
vn flag
Bob

I have been playing with SHA-2-256 in Julia and I noticed that the hashes produced don't appear to follow a uniform distribution. My understanding of secure hashing algorithms is that they should approximate a uniform distribution well, so they are not predictable.

Here is the Julia code I'm using:

using BitIntegers, Distributions, HypothesisTests, Random, SHA

function sha256_rounds()
    rounds::Arr ...
Score: 1
헬창공돌이 avatar
What if the other user generate the Session Key rather than KDC for Key Establishment
cn flag

I m studying for the Key Establishment Using a Key Distribution Center From my understanding, KDC contains all the users' private keys. For example, If Alice wants to talk with Bob, Alice requests to the KDC by using Request(IDAlice,IDBob) and KDC generates the random session key and encrypts the session key with Alice's Key and Bob's key. Alice receives the encryptwithAliceKey(SessionKey),encryptwithBo ...

Score: 0
VitoShade avatar
QKD measuring qubit with wrong bases
cn flag

I'm trying to end the research work for my master thesis about BB84 QKD (and QBC) and a basic problem of quantum mechanics is blocking me.

I'm trying to do a probability calculus of the action of measuring a qubit in a wrong bases. In bibliography, I've always found the statement:

When Bob chooses the wrong bases for measuring a qubit then the result will be completely random.

But what exactly d ...

Score: 2
Chirag Parmar avatar
Difference between fuzzy vault and fuzzy commitment?
cn flag

https://dl.acm.org/doi/10.1145/2905055.2905118

Quoting the above paper's abstract, "Biometric cryptosystem can apply fuzzy vault, fuzzy commitment, helper data and secure sketch, whereas, cancelable biometrics uses distorting transforms, Bio-Hashing, and Bio-Encoding techniques."

It differentiates between a fuzzy vault and a fuzzy commitment scheme. How are the two different? Where does fuzzy ext ...

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