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17 views

Why do we use prime numbers apart from hard factorization?

Why are prime numbers important in cryptographic constructs? I am not interested in RSA examples where factorization is the hard problem itself, that makes sense. However wherever I go I encounter ...
1
vote
1answer
45 views

Difference between Key Scheduling and Key Generation?

I am a little bit confused in the terms i.e Key Scheduling and Key Generation. What is the actual difference between these two terms? According to Wikipedia, the terms are described as: Key ...
1
vote
0answers
40 views

Any speed up methods for finding the index of a random value produced by the Inversive congruential generator?

The Inversive congruential generator produces random values with: $$x_{n+1} = a\cdot x_{n}^{-1} + b \mod P$$ (special case if $x_n=0$ -> $x_{n+1}=b$) starting with an initial value $x_0$ With well ...
0
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0answers
7 views

What does the server do on receipt of a one-time-password?

I'm trying to understand this question and I do not understand part of it. I have part of figured out, part of it not. Considering the hash function h(i) = (i + 5) mod 7, used in an implementation ...
0
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0answers
16 views

NTRU Key Exchange

With the NTRU scheme, is the key exchange only done by encrypting a symmetric key with the recipients public key (+ authentication) or can something similar to DH/ECDH be done, where public ...
0
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0answers
26 views

If there is an algorithm A can calculate the modular square root of input n, How to use it to get prime factors?

Suppose you are given an algorithm $A$ which takes $y \in \{0, 1, \ldots , N − 1\}$ as input, and outputs $x \in \{0,1,\ldots,N − 1\}$ such that $x^2 \equiv y \pmod{N}$. Design an efficient, ...
1
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1answer
36 views

Is there a point in storing hash or plaintext in the last column of Rainbow Tables

As I read up on rainbow tables, I found that most sources suggest storing a plaintext - the result of Rk(hk) - in the last column, while others just store the hash hk, basically stopping one step ...
1
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1answer
34 views

Difference between Tag and Signature

Is there a technical difference between tag such as tag generated by authenticated encryption, and signature such as the signature generated by a functional signature scheme or homomorphic signature ...
2
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1answer
63 views

Index Calculus for Discrete Logarithm

I'm studying the Index Calculus method for Discrete Logarithm. In the book "Introduction to Cryptography with Coding Theory" by Trappe it's told that, if $$\alpha ^{k}\equiv \prod p_{i}^{a^{i}} \quad ...
2
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1answer
807 views

Square roots, prime factorization

I´m stuck in my homework and since its homework, I would rather get some hints than full solution. The problem goes: factorize n = 88416763 in case that you know that the square roots of 51733469 (...
0
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0answers
57 views

Difficult problem proposal

We start working with the Ring $R=\left(\mathbb{Z}/p\mathbb{Z}\right)\left[x\right]/\left(x^{3}-1\right)$, $p$ prime, i.e. degree two polynomials with coefficients modulo $p$ modulo $x^{3}-1$. As $x^{...
0
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1answer
58 views

Why does curve25519 use a cofactor of 8?

This cofactor (as I understand it) effectively discards valid points that satisfy the curve equation over the finite field. Why would one wish to reduce the number of possible private keys, it seems ...
2
votes
1answer
140 views

Do any NIST PQC have “homomorphic” public keys, in the sense that any two pubkeys derive a combination pubkey?

Background: The MathMesh crypto platform (refs at the bottom) is a newly-proposed technology stack which has been somewhat cheekily called a "Grand Unified Theory of Security on the Internet". Its "...
10
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1answer
5k views

Are hash functions strong against quantum cryptanalysis and/or independent enough of mathematics?

I work on ethereum and other blockchain technologies. And seeing that quantum pc's are someday going to see the light I have some questions / doubts. I was wondering if hash functions are strong ...
2
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2answers
84 views

RSA exercises example

I have doubts about this question Consider the following textbook RSA example. Let be p = 7, q = 11 and e = 3. Give a general algorithm for calculating d and run such algorithm with the above ...
-1
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1answer
39 views

Random oracle : Replay

What I understand about the random oracle game: The adversary can query the oracle polynomial many times with the same (secret but unknown) key. From the output returned by the oracle, the ...
0
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0answers
15 views

Key exchange and authentication using libhydrogen

I have been able to exchange session keys on two devices using Libhydrogen's Key exchange using the N variant method. I also want to authenticate both devices to have some protection against the Man ...
0
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1answer
55 views

Can a One way function also be its inverse?

This is from my homework: Prove that if there exists a one-way function, then there exists a one-way function f such that $f(0^n ) = 0^n$ for every $n$. Note that now for infinitely many values $y$...
4
votes
1answer
119 views

Minimum number of independent trials needed to detect a bias [closed]

Suppose, I suspect that the probability of occurrence of a particular bit as $0$ is $.558$. Since, it is not $.5$, so this is possibly a bias. Now, my question is: What is the minimum number of ...
0
votes
1answer
22 views

difference between function f in eval and dec of homomorphic authenticated encryption

In the homomorphic authenticated encryption, as described 1, there are Eval and Dec PPT algorithms: In Eval, f is the function to be performed on the encrypted data. However, I need to know why it ...
0
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1answer
41 views

Why does using a prime-order subgroup in DLP improve security?

Let's consider a discrete logarithm $\beta \equiv \alpha ^{x} \bmod \,\, p$ We can solve it using Pohlig-Hellman algorithm. And, if $p-1 = tq$ where $q$ is a large prime factor, we can avoid any ...
0
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1answer
36 views

Does the nonce really have to be hashed as part of the challenge in a Schnorr signature?

From this article: https://tlu.tarilabs.com/cryptography/digital_signatures/introduction_schnorr_signatures.html#why-do-we-need-the-nonce The article states that the challenge ...
1
vote
1answer
34 views

Is a Diffie-Hellman scheme in which parties always use the same public keys vulnerable?

I have come across a couple of protocols in which the public keys of the parties are static across conversations, even with different users. Something about this makes my hairs stand on end but I can'...
0
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0answers
45 views

Some curiosity about HMAC

Is the probability of distinguishing HMAC from a random oracle is the same as the probability of forging HMAC? Can we say that the following statement is trivial? $\Pr[\text{Forging $\operatorname{...
0
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2answers
51 views

Does HMAC provide anything that AEAD does not?

Alice and Bob have to talk through Eve. (server to device through untrusted third party that relays messages, no TLS available) Assume a secure key. Out of scope. Example, ECDH key exchange with HKDF....
1
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0answers
65 views

Is bit encryption enough?

Assume that $\Pi$ is a secure PKE scheme (or other appropriate encryption schemes) with 1-bit message space. And it can be applied bit-by-bit to construct a many-bit encryption scheme $\Pi'$. ...
0
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0answers
20 views

Few confusions around PKI and breaking SSL [on hold]

I have been studying the ways of PKI for some time now, and get confused quite a bit in a few specifics. Problem 1: Firstly, We use the Bob and Alice analogy when we read something, but in real ...
3
votes
1answer
264 views

Detecting steganography by analysing non-significant data entropy?

I am not thinking only steganography in images, I think it is also possible to encode data for example into the length of spaces of a clear html text. I suspect, the steganography changes (elevates) ...
2
votes
1answer
760 views

Database and End-to-End Encryption

I'm currently designing a mobile/desktop application to synchronize some messages or notes. I'm searching for a way to secure it and to avoid letting the server be able to read the messages. My goal ...
0
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0answers
34 views

Should I proceed with this for my project? Is it correct?

We have: Select five Prime numbers $p$, $q$, $r$, $s$ and $t$ Compute $n=p*q*r*s*t$ Calculate $Φ(n)=(p-1)(q-1)(r-1)(s-1)(t-1)$ Collect $e$ such that $p < e < Φ(n) … Φ(n)$ and $n$ are co-prime ...
1
vote
1answer
110 views

Birthday attack on hash functions derived from a collision-resistant hash function [on hold]

$H_1$ is a collision-resistant hash function with an $L$-bit output. 2 hash functions are created based on it as follows: $$H_2((k_1,k_2);m) = (H_1(k_1;m), \space H_1(k_2;m))$$ $$H_3((k_1,k_2);(m_1,...
0
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0answers
41 views

Problem on RSA modification [on hold]

I'm working on the security of the cloud using RSA encryption algorithm. I need help with the simulation of the RSA algorithm against the modified RSA algorithm. Instead of the two prime number , I ...
0
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0answers
17 views

AEGIS/MORUS as a general purpose hash function

Can AEGIS/MORUS, ignoring its output except the tag and with a fixed key and IV, be used as a general purpose cryptographic hash function?
2
votes
1answer
338 views

Cracking a key using a combination of partial keys

As part of a cryptanalytic attack I've carried out, I used a divide-and-conquer strategy to divide the secret key $k$ into several equal-sized partial keys $k = {k_1, k_2, ...}$. The attack works ...
-1
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0answers
26 views

Diffie-Hellman key exchange in four parties [on hold]

I understand the concept of 2 and 3 parties Here is the code of 3 parties ...
2
votes
1answer
29 views

What is the main difference between Unique signature and Verifiable Random Function?

The output of VRF contains two parts, the first is the output of the VRF hashing and the second is the proof of correctness. In a unique signature scheme, the signature also contains two parts which ...
-1
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0answers
41 views

RSA attack using chinese remainder theorem [on hold]

After encryption same message for 3 different people using their public key (187, 3), (35, 3), (247, 3) there are cryptograms (109, 15, 208). What is that message? Use chinese remainder theorem. ...
0
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1answer
32 views

How to calculate base value in modular exponentiation

If you have $a^b \bmod n = c$, and $b,n,$ and $c$ values are given, is it possible to find a value for $a$ within a given range? So is it possible to find $a$ in $a^{2051} \bmod 3149=636$ knowing a ...
5
votes
2answers
140 views

If a new hash function were made that simply truncated sha-256 to the first N bits, how much insight would it provide into sha-256?

Clearly it would provide perfect insight if all 256 bits were used. What about if 255 were used? Would the general behavior and properties of "sha-255" be expected to be close to sha-256? What about "...
0
votes
1answer
35 views

Two possible plaintext's using OTP decryption

I am using this cipher-text c = 04 10 12 00 01 08 67 0A 19 65 0F 03 0A 00 with two possible keys ...
11
votes
3answers
1k views

Why is the core ChaCha primitive not good for use in a CRCF? Why create BLAKE?

Why is the core ChaCha primitive not good for use in a collision-resistant compression function (crypto hash)? Why go through the trouble to create BLAKE? What's wrong with using the core ChaCha ...
2
votes
1answer
27 views

Simply using password as a third “private key” for PAKE

I'm reading through the development of PAKE protocols, starting with EKE and SPEKE, their potential pitfalls, and what motivates their protocol choices. And I've been wondering, what is wrong with the ...
0
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0answers
21 views

How would you decrypt an affine cipher with only the ciphertext? [duplicate]

If I have only the ciphertext but the alphabet and the value of a and b are all unknown ... how would I go about this? I understand decryption with the key and alphabet, that is fairly easy but if we ...
0
votes
2answers
65 views

Elliptic curve commitments mod p

As far as I understand secp256k1 is defined over the group p with p = FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFE FFFFFC2F I don't really ...
1
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0answers
24 views

How many ring-LWE samples are required for the (Search) Ring Learning With Errors problem to have a unique solution?

Consider the LWE distribution $\{(\pmb{a}_{i},\left<\pmb{a}_{i} , \pmb{s}\right> + e_{i})\}$ where secret $\pmb{s} \in \mathbb{Z}_{q}^{n}$, randomness is $\pmb{a}_{i} \xleftarrow{\$} \mathbb{Z}_{...
0
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0answers
25 views

What encryption / cryptography method is used here? [on hold]

I have no clue what sort of encryption is used in this piece. Does anyone has any clue? The only information I got is that the dots represents a space.
0
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0answers
21 views

How do I go about managing keys? [on hold]

I need a way to send a message and need a way to guarantee integrity and authenticity. I want to use HMAC but how do I go about using the public/private keys? And how do I get them?
4
votes
3answers
214 views

How can frequency analysis be applied to modern ciphers?

I am building a computer program that deciphers Caesar, Vigenere and monoalphabetic substitution ciphers. All of those are susceptible to frequency analysis. However, it does not seem to be real-world ...
0
votes
1answer
23 views

decrypting a shifted cipher message without knowing shifting parameter in advance [on hold]

helo - i was wondering, if i know the message (after it been shifted), is there some smart way to decrypt it? (i don't know in advance by how much it been shifted). all i know is this is the message, ...
0
votes
0answers
26 views

I have been given a challenge to solve a string wich results in a word [on hold]

The string that i have been given is this; LKamdakW23MMDD22/23nmDlMNDwnn/ksnaw1827das82bka6/1244nfk2n3k1== I am only told that it contains a word/s When i first recieved this challenge i tried ...

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