1
vote
1answer
130 views

Hash function as secure as one-time pad?

We know that the one-time pad is provably secure as a cipher to encrypt some data. Is there an algorithm which does the same just as a hash function? Can we get a provably secure hash function? Maybe ...
1
vote
0answers
42 views

Boneh-Boyen like signature scheme

Full Boneh-Boyen signature scheme defines a pair of secret keys (SK) $a \in \mathbb{Z}_n$ and $b \in \mathbb{Z}_n$ and a pair of public keys (PK) $A = G^a \in \mathbb{G}$ and $B = G^b \in \mathbb{G}$. ...
1
vote
1answer
160 views

Additional Data in AEAD (Chacha20-poly1305 libsodium)

I have recently been playing with Chacha20-Poly1305 with libsodium, and all of the examples state the additional data portion of the tag is stored in plaintext when encrypted. But from what I can tell ...
4
votes
2answers
197 views

Is $f(x)\oplus x$ a one-way function?

Given that $f$ is a OWF and $|f(x)|=|x|$ for all $x$, is $g(x)=f(x)\oplus x$ necessarily also a OWF?
1
vote
0answers
319 views

Trivium example

I started learning cryptography from Understanding Cryptography book of Christof Paar and Jan Pelzl. Here is the problem I have solved but I want to be sure that it is correct. Assume the ...
1
vote
1answer
121 views

Misunderstanding Broadcast Encryption

I have a secret message which I want to encrypt such that any of several different keys can open it independently. The keys can't know about each other and it has to be able to work completely ...
1
vote
1answer
90 views

Why is knowing M not enough to break Blum Blum Shub?

In Blum Blum Shub, the generator is $x_{n+1}={x_n}^2 \mod M$ where $M=p \cdot q$, $p \in \mathbb P$, and $q \in \mathbb P$. Supposedly, knowing $p$ and $q$ is enough to break the system. But if I know ...
3
votes
1answer
191 views

Given $g^a, g^b, g^c, g^{1/b}$, is it hard to distinguish $e(g, g)^{abc}$ from a random value?

where $g$ is a group element in bilinear group $\mathbb{G}$. I understand it is very similar to the conventional DBDH problem, but $g^{1/b}$ is also known, possibly making it easier? Does anyone know ...
2
votes
2answers
99 views

Is there any advantage on encrypting the CMAC together with the message?

I'm reading a protocol specification where the procedure is to generate a CMAC, take the first 4 bytes of it, append this authentication tag to the message and then encrypt the message + CMAC together ...
0
votes
1answer
54 views

Stream cipher key length to send

I was being argued that stream cipher's key that is the length of the message must be sent to the destination for them to be able to decrypt the message. My point is don't you only have to send the ...
1
vote
1answer
78 views

Can you exchange a shared key without any hardness assumptions?

Imagine that P=NP, and one way functions don't exist. Can two people end up with a random shared key of arbitrary length, if every exchange is public? They have true RNGs, and know who they are ...
0
votes
0answers
59 views

compression with codebook and Cryptography

a question about the difference between code book based compression method and key based cryptography. As I know Crypto != Compression. The Shannon said Crypto is try to reduce the information of ...
2
votes
3answers
170 views

Sage Vs C++(with NTL) for implementing cryptosystems

Is Sage a better alternative to C++(with NTL), for programming that involves math objects like polynomial rings in cryptosystems? I hear that Sage is an open source alternative to Magma. I have used ...
1
vote
1answer
69 views

Noisiest RF band for random number generation

I've been looking into the difference between PRNGs and proper RNG techniques. One that I particularly like is the idea of tuning a radio to a certain frequency and bandwidth and just listening to the ...
-1
votes
1answer
79 views

Generating cyclic group for Ciphertext-Policy Attribute-Based Encryption [closed]

I am doing Project under the topic CP-ABE.I need to generate a symmetric bilinear group Go of prime order p and with generator g...Then how to choose random elements from Zp....kindly anyone help ...
1
vote
1answer
40 views

What does K stand for in frequency analysis

It was from frequency analysis lecture and the professor mentioned but I cannot recall. The K value for English was .067, German was .076. The lowest K was Russian which was .056. When the frequency ...
4
votes
1answer
277 views

Does using modulo (%) affect quality of randomness?

I'm writing a small script that generates random non-signed decimal integers within a certain range of values. I'm using GNU od, with the following command: ...
-1
votes
2answers
148 views

How fast would a polynomial time factoring algorithm compute?

I know factoring is the chief means of breaking RSA keys. I know an algorithm that runs in polynomial time would be able to break an RSA key pair "quickly". But how quickly is "quickly"? Note, I'm not ...
0
votes
2answers
156 views

Client-Server application how can data be encrypted so only clients can read it

Requirements We are building a system that connects multiple clients through a restful API. It allows the creation of groups of trusted clients. We need a way to store group shared data encrypted ...
0
votes
2answers
98 views

Counter Mode with a sequence of zeros bits plaintext, is it secure?

I had a quiz last week in computer security course. There was a confusing question that I am still looking for a good and clear answer. First, I know that counter mode with a good block cipher is ...
1
vote
2answers
47 views

Automatic generation of secure passwords with the least inconvenience for a user

I'm working on a web site for a private company that should allow them to upload files, which will be later retrieved by their affiliates. The site will be available from a public Internet using ...
1
vote
0answers
34 views

ssh-keygen bit why not use 4095 or 4097? [duplicate]

All examples of using ssh-keygen I have seen has always been some power of 2 (2048, 4096). ssh-keygen -t rsa -b 4096 Why use those numbers? Why not use 3333? ...
0
votes
1answer
70 views

Weak Boneh-Boyen Signature in Composite order group

In the paper Ring Signatures of Sub-linear Size Without Random Oracles, authors have remarked that the scheme is instantiable in composite order setting, too. I am attaching the following reference ...
0
votes
1answer
41 views

Using Permutation polynomial to compute a MAC

Is the following MAC secure? For a block $y_i$ in a file, we defined a MAC as follows: $Mac_i:PRF(k,i) \cdot g^{y_i \cdot r_i} \bmod p$. Where $p$ is a prime number, $g \in \mathbb{G}$,$PRF(k,i)$ is ...
1
vote
1answer
105 views

PRF based on the GGM construction

What's the differences between the concepts “pseudorandom generator” and “pseudorandom number generator”? In fact, I want to implement a pseudorandom function based on GGM's construction at ...
0
votes
0answers
101 views

Python implementation of a blind signature scheme which doesn't involve RSA

RSA seems a bit creepy after the Snowden revelations and i'm looking for a simple python based blind signature library to fiddle around with. So far i've been unable to find anything. What am i ...
1
vote
1answer
58 views

How do you derive the lambda and beta values for endomorphism on the secp256k1 curve?

You can see a little background about this on this bitcointalk post by the late Hal Finney. $\beta$ and $\lambda$ are the values on the secp256k1 curve such that: $$\begin{align} \lambda^3 &= 1 ...
2
votes
1answer
194 views

SHA1 Partial Collision

I'm working on a little python script that reads in two fairly similar English sentences (they're in text files - reading them in) and I'm trying to force a SHA1 partial collision (e.g. first 32 bits ...
1
vote
1answer
234 views

What is the difference between a hash function and a pseudorandom function? [duplicate]

Read the title. I've seen in RFCs that some MAC functions are called "pseudorandom functions". What are those? How are they different than hash functions? Why can't a hash function be used instead?
0
votes
1answer
97 views

CPA security of a stateless and deterministic encryption system

Why can no stateless and deterministic encryption system be IND-CPA secure? Is there a formal proof for it?
0
votes
2answers
95 views

RSA generation of private key using public key

In RSA private key generation e*d ≡ 1 mod φ e is public, also n is public. How to prove mathematically, generation of ...
0
votes
2answers
124 views

Multiple encryption of part of block

Is there any security risk in encrypting parts of blocks twice? I'd like to get around block sizes and make encrypted messages just as long as the unencrypted ones: Block 1: Byte 0 - 7 Block 2: Byte ...
0
votes
1answer
96 views

Definition of ciphertext security

If I got it right, chosen ciphertext security implies also CPA security. In other words, attacker can submit plaintexts to the challenger (along with ciphertexts). I do not understand why ...
0
votes
0answers
54 views

Decrypt a message which is encrypted using XOR? [duplicate]

This is a puzzle asked in a contest. Given that encryption , decryption happens as per following rule/code: ...
1
vote
0answers
88 views

Existence of encryption schemes where $F_{k}^{-1} \big( F_{k}(A) + R \big) = A + O(R)$

Is there a encryption scheme in literature, where I can do something like $$F_{k_1}^{-1} \big( F_{k_2}(A) + R \big) = A + O(R)$$ where, $A$ is a $m \times n$ real matrix, $R$ is a $m \times n$ real ...
0
votes
1answer
190 views

Why does the DES crypto algorithm NOT use 2 rounds?

Now, if we were to go round by round, you could give a distinct reason for not using a single round since after just one round, the right half of the text comes directly, as-is, to form the left half ...
0
votes
2answers
263 views

Generation of a cyclic group of prime order

I am trying to implement a cyclic group generator in Java, but I am running into some issues. In many cryptosystems, the following phrase is expressed during the key generation stage. Let G be ...
0
votes
0answers
23 views

Kryptos K2 keyword derivation [duplicate]

So I've been doing some reading on Kryptos, and to be honest the keyword for K2, ABSCISSA, has a pretty weak derivation. (The method using the eee's). Isn't there a better way to come to that? I dont ...
0
votes
1answer
65 views

Non-repudiation and digital signature of a dishonest participant

Let's assume a dishonest Alice who sends, encrypts & digital signs a message to Bob. Bob stores the decrypted message and the digital signature in a database. However Alice is a bad girl and ...
0
votes
1answer
99 views

XOR cipher with three different ciphertexts and repeated key, key length known. How do I find the plaintexts?

Let us say we have three different plaintexts (all alphabets, A-Z): $x$, $y$ and $z$, each of length $21$. Let the key, $a$, be also of length $21$. Now, what we have is $x \oplus a$, $y \oplus a$ ...
0
votes
1answer
54 views

Why is it a quadratic equation?

In Groth-Sahai NIZK proof system, they have defined something called Quadratic Equation in $\mathbb{Z}_n$ as shown below. But, my idea of quadratic equation was a second order polynomial equation in a ...
5
votes
0answers
116 views

Parallel Pollard's Rho: Number of distinguished points

When using the parallel version of Pollard's Rho algorithm for discrete logs, each processor performs its own random walk to find distinguished points, and reports the starting point and the ...
2
votes
2answers
61 views

One-way function definition

I cannot understand why a one-way function $f$ is defined in this way $\text{Pr}(f(A(f(x))) = f(x)) < \frac{1}{p(n)}$ and not $\text{Pr}(A(f(x)) = x) < \frac{1}{p(n)}$ where $A$ is a ...
0
votes
1answer
96 views

Proof that $gcd(e, \lambda(N)) = 1 \hspace{1mm} \Longleftrightarrow \hspace{1mm} gcd(e, \varphi(N)) = 1$

What is the proof for the fact that $gcd(e, \lambda(N)) = 1 \hspace{1mm} \Longleftrightarrow \hspace{1mm} gcd(e, \varphi(N)) = 1$ Where: $N = P * Q$ where $P$ and $Q$ are both primes. $\varphi(N)$ ...
1
vote
1answer
45 views

Do any stream ciphers with aperiodic keystreams exist?

Exactly what it says on the tin. I can imagine constructing such keystreams from: The binary expansions of irrational numbers Chaotic systems like the logistic map or the Lorenz attractor. The ...
0
votes
1answer
89 views

One time pad probability

I'm trying to solve a question about one time pads but I'm not sure if my assumptions are correct. I am to assume that I have a one time pad with perfect secrecy. This one time pad is used to ...
0
votes
0answers
25 views

Reducing key shares in Damgård-Dupont threshold RSA

I'm working on understanding and implementing Damgård, I., & Dupont, K. (2005). Efficient Threshold RSA Signatures with General Moduli and No Extra Assumptions. Public Key Cryptography-PKC ...
0
votes
0answers
27 views

Proving the complement property of DES? [duplicate]

I'm trying to show that for a given plaintext (P), key (K), and cipher (C) in the DES algorithm: ...
0
votes
1answer
56 views

Is there a reference that prove that the AES Key Schedule generate random looking round keys?

Starting from uniformly random generated AES master key, is there a reference that prove that an specific roundkey can be considered as uniformly random generated as well ?
4
votes
1answer
233 views

How hard is it to find plaintexts whose hashes satisfy $h(a)\oplus h(b)=h(c)$?

Given a cryptographic hash function $h$, for example SHA256, how hard is it to find plaintexts $a,b,c$ such that $$h(a)\oplus h(b)=h(c) \text?$$

15 30 50 per page