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6 views

Polyalphabetic rotation cipher over digits

what is the keyspace of a poly-alphabetic rotation cipher over digits, with a repeated key-length of 2, in which no digits can encrypt to itself? Why is the answer 72?
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0answers
25 views

Hash functions producing 48-bit hash?

Could you please list hash function algorithms producing 48-bit hash for checksum?
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0answers
25 views

Why doesn't WhatsApp encryption multiply file size

WhatsApp uses and end-to-end encryption, on both personal and group chats. According to my understanding, that means every message I send to a group is encrypted on my Device for every group member ...
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0answers
25 views

What hash function? [on hold]

input: "HqDkJnxGdf.NjNQnTxaeC41pwi0WDvD6Rl2a7-GnfxY.35303.34720" hash: acdf608df8b8 input: "HqCELbAzF2.NjNQnTxaeC41pwi0WDvD6Rl2a7-GnfxY.34326.34720" hash: 742f26dd9e14 input: "HqCELbAzF2....
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1answer
56 views

Order of subgroups formed by Elliptic Curves with a Cofactor

In this question: Why are the lower 3 bits of curve25519/ed25519 secret keys cleared during creation? The answer indicates that the order of all points on the curve over the finite field ...
1
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0answers
30 views

Does SET in any way use SSL?

I just started a course in web security, and I was just wondering quickly if SET in any way would use SSL? I noticed it was developed in part by Netscape. But all I can find is comparisons between the ...
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0answers
16 views

How to perform ByteSub transformation? [duplicate]

Can anybody please tell me how do we perform ByteSub transformation of AES to 01001001.
2
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3answers
404 views

Why are in asymmetric cryptography as many keys as people involved needed?

The question: "10 friends wish to establish secure communications between themselves using asymmetric-key cryptography. How many keys need to be known by each user?" was posed by my teacher. He says ...
-1
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0answers
25 views

How to show that Affine crypto have a valid decryption

I just need to know how to attack a question I have in my textbook this is like: Let $E_1 (x) \equiv 17x + 7 \pmod{28}$ and $E_2(x) \equiv 23x + 11 \pmod{28}$ be encryption functions for two ...
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0answers
17 views

Will CT (Certificate Transparency) override the use of CAA and/or DANE/TLSA records?

I'd want to know if some of these competing technologies has more chance to survive. It seems they are thought to solve a similar problem by different manners and I'd want to stick to the most ...
0
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1answer
38 views

Generate private key from public key RSA

I am doing a tutorial where my lecturer (PhD) gave me an optional question to do relating to RSA. He said: write a python function that takes as input the server’s public key and then uses that to ...
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0answers
28 views

What are the advantages of runtime defenses vs. compile-time defenses against buffer overflow? [on hold]

What are the advantages of runtime defenses v compile-time defenses against buffer overflow attacks?
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1answer
48 views

Text encryption algorithms that can be used and are secure

what text encryption algorithms are being used nowadays that are secure? Obviously I am not interested in DES or 3-DES that google shows me and which can break...
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2answers
55 views

What is a multi-target attack on block ciphers?

What exactly is a multi-target attack on a block cipher? How does the attack work? How can it be avoided?
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0answers
17 views

Zero knowledge proof that ElGamal ciphertext encrypts the opening of Pedersen commitment

Given ElGamal ciphertext for a message $m$ with a random $r$ as $(c_1,c_2) \gets (g^r, g^my^r)$ for a public key $y$, and a Pedersen commitment $C \gets g^xh^r$, I have been able to create a proof ...
3
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1answer
239 views

Is length extension attack considered as collision?

I came across a few articles about length extension attacks on cryptographic hash functions. I was very surprised to read that SHA-256 and SHA-512 are prone to length extension attacks. This seems ...
0
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1answer
63 views

Choice of finite fields for use in elliptic curves

this is maybe a basic question but I'm trying to better understand elliptic curve cryptography at a fundamental level. I understand that a finite field is required in order to define a boundary for ...
-1
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0answers
32 views

one hash for two (or more) different input values

I build an application that has to interact with legacy applications (outside zone of control). There are shared entities (medicines, pharma companies) between my and legacy apps. Each legacy app ...
0
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0answers
11 views

Is there any existing Threshold Authorization Token?

By Threshold Authorization Token I mean a token (similar to a JWT) that is produced by a (t,n)-threshold scheme. I'm trying to gather background on the subject, but it's hard to find anything, if ...
1
vote
1answer
35 views

RSA decrypt message with low public exponent (n = 187, e = 3 and C = 185)

n = 187 e = 3 C = 185 How to decrypt message? I know there is some way using cryptogram exponentiation. Can you give me a hint?
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0answers
16 views

Zero knowledge proof with accumulators

I am working on a proof of concept on cryptographic accumulators. delta: The current size of the tails file in the accumulator. witness: The current value of the accumulator when the entry of your ...
0
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0answers
40 views

Where are labels of a Labeled data used in homomorphic message authenticator stored?

In a fully homomorphic message authenticator, Alice can authenticate some large data $D$ using her secret key $s$k. She chooses a label $\tau$ for it, and the authentication algorithm authenticates ...
-2
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0answers
18 views

Change windows live mail password?? Issue [on hold]

Gentlepersons, I am using Windows Live Mail as my e-mail program at the moment. I've been using it without a question for several years ... until recently. I've had problems with changing my e-mail ...
1
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1answer
46 views

Do garbled circuits run in constant time?

It seems like garbled circuits should not be input dependent, and hence should always run in constant time. Just wanted to clarify if this is true.
1
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1answer
49 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
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0answers
24 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 ...
2
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1answer
48 views

Is a keyed MAC sufficient for integrity protection?

I'm working with the above figure which shows a challenge-response protocol. ...
0
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0answers
29 views

NTRU Bilateral 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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1answer
48 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, ...
0
votes
1answer
77 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 ...
1
vote
1answer
43 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 ...
0
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0answers
23 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 ...
1
vote
1answer
106 views

Is this problem based on discrete polynomials modulo $(x^3-1)$ strong?

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
28 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 ...
2
votes
1answer
158 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 "...
0
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1answer
48 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 ...
1
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2answers
63 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
votes
1answer
81 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 $$\alpha^k\equiv \prod p_i^{a^i} \mod p$$ ...
0
votes
1answer
59 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
43 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
22 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 ...
0
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2answers
62 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....
0
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0answers
53 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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0answers
38 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 ...
0
votes
1answer
68 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 $y$...
3
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0answers
91 views
+100

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
20 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?
0
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1answer
42 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 ...
-1
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0answers
42 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. ...
-1
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0answers
27 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 ...

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