All Questions

0
votes
0answers
5 views

Is salt bring more security for digital signature!

Is it good idea to use salt in digital signature? Is it bring more security? If so, I should use it for key or the message?
0
votes
0answers
9 views

Recover a secret message in a .wav file

First, I apologize for my english, I'll do my best. On my computer, I got a .wav audio file that hides a secret message. I want to recover that message. But I'm stuck and I need your help :). My ...
0
votes
0answers
15 views

How does hash function in Elgamal signature scheme prevent existential forgery attack?

I have heard that hashing the message M prevents an existential forgery attack. I was wondering how.
2
votes
2answers
36 views

Real life systems that use concepts of crypto computing

Are there any working cloud/internet solutions/products that operates on encrypted data such as systems using homomorphic encryption, secure multiparty computation, electronic voting, private ...
0
votes
1answer
41 views

Addition / Multiplication modulo 13

I am currently studying Diffie-Helman protocol. In my lecture notes I have a generator g=2 and I'm in group $Z_{13}^*$ . There I calculate a remainder cycle from 1 to 12 with $r =g^i \mod 13 \forall ...
0
votes
0answers
38 views

PHP secure random number generator

I was trying to find a better way to generate random numbers in PHP and thought that using /dev/urandom would be the way to go (based on a few lectures). So I thought I would implement the following, ...
0
votes
0answers
12 views

Change of axis positions in Vigenere Square

Is there any history of codes in which there have been changes in the normal axis positions of the Vigenere Square? Have been working on a code which has two non-normal positions -- one with the ...
0
votes
1answer
41 views

Python. RSA common modulus attack problem

I have: N = /*500 decimal numbers*/ E1 = 3740453 E2 = 4226171 M^E1 = /*500 decimal numbers*/ M^E2 = /*500 decimal numbers*/ I must use RSA common modulus ...
1
vote
2answers
47 views

Bilinear Map vs Inner Product

What is the difference between a Bilinear Map and a Inner Product?
2
votes
0answers
25 views

Gap problem for Learning With Errors

Informally, a "Gap" problem is the one that arises when solving the computational (or search) version using an oracle for the decisional version. For example, the Gap Diffie-Hellman Problem (GDH) is ...
1
vote
0answers
34 views

Can a secret message be securely transmitted within a MAC tag?

A sender wants to transmit an ultra secret code $M$ which could be either 'go', 'stop' or 'wait'. This could be any selection of code words really and adopted for any use such as transmitting short ...
0
votes
0answers
20 views

java.util.Random and Dice Rolls

For this question, a dice roll will be considered two 6 six sided dice, to give a possible output of 2-12. Given a java.util.Random instance r, the output of one roll would be: ...
0
votes
1answer
32 views

What Java actually stores inside Keystore when generating Keys?

When we use Keytool to generate a Keystore to store Private/Public keys, what Java actually stores inside the Keystore file ? I ...
0
votes
0answers
19 views

Problem description “SAFE” [on hold]

So this is the problem, sorry for the bad img quality. The answer which i don't know is 10 chars long. And there are thease 3 safe knobs with numbers inside them. I have been trying to solve it,yet ...
0
votes
0answers
21 views

Designing hash function in space-efficient identity based encryption

Let $n$ be an RSA-prime and we know prime factorization of $n(=pq)$. The hash function is the current context maps from a given user identity(id) to a positive integer less than $n$, whose jacobi ...
-1
votes
0answers
18 views

CBC-MAC, possible attack that violates computational resistance

received this question in an assignment and figured the wizards of crypto.stackexchange could give me some useful and relevant input. Suppose an attacker knows three message/CBC-MAC pairs $(M_1 , ...
1
vote
1answer
77 views

Hash collision using the leading 40-bits of SHA-1

I am trying to implement Floyd's cycle finding algorithm for finding a leading 40-bit hash collision in the SHA-1 algorithm. However, my code will not find a repetition even with 800,000,000 hashes. ...
2
votes
0answers
35 views

Are all binary-additive stream ciphers reciprocal?

I'm writing a thesis focused on Maurer's provably-secure stream cipher. Long story short, this cipher works by expanding a short key into a long keystream and then XORring this keystream with the ...
2
votes
1answer
61 views

What is the difference between order of base point and curve order in EC?

When I was read about the elliptic curve cryptography I found some definition about domain parameter of elliptic curve like the follow. But I did not understand something $p$: prime number. $a, b$: ...
5
votes
0answers
91 views

Verbatim of early work on public-key cryptography?

In late 1997, the history of public-key cryptography was turned around with the announcement by the CESG (April 2000 archive) that public-key cryptography was theorized in a 1970 note [1] by James ...
1
vote
0answers
18 views

Is there a Javascript and Java implementation of a good CSPRNG [on hold]

I need to use a cryptographically secure pseudo random number generator in my client running Javascript and in my server running Java. Is there a well-known implementation of a good CSPRNG in both ...
1
vote
1answer
35 views

Proving correctness of a decryption of a homomorphically summed ciphertext?

I would like to take some additively homomorphic cryptosystem - don't care much which one for now - and encrypt a series of numbers with it. I would then like to (in public) take these numbers, add ...
0
votes
0answers
35 views

Difference between signing with SHA256 vs. signing with RSA-SHA256 [on hold]

I play with digital signatures using node.js (server side JavaScript, built on Google's V8 JS engine). There is a "crypto" module included. For test purpose, I created a digital signature of some XML ...
0
votes
0answers
39 views

Cryptographic Operations and Security

sign((M’, TAlice, sign(( encrypt(( encrypt(M, KpbBob), M’), K), TBob), KsBob)), KsAlice) Can you tell me six security-related facts ...
0
votes
2answers
61 views

Availability of a simple limited PRNG algorithm

I am in need of a really simple limited PRNG, that either exists or can easily be created in virtually any language on any platform. It takes only the initial seed, and is only expected to generate a ...
0
votes
0answers
50 views

Is there an “additive” proof-of-work?

I'm trying to find a proof-of-work algorithm with the following properties: If A(1) is a proof of work with Difficulty(A(1))=n (requires n basic operations on average), then one can find a proof of ...
0
votes
0answers
44 views

Should I study advanced abstract algebra and more than elementary number theory to pursue a career in cryptography?

Do I need to study advanced abstract algebra and more than elementary number theory in order to pursue a career in cryptography ? I've already taken a course in abstract algebra, but I'm wondering ...
1
vote
1answer
63 views

To prove $r \cdot f_1 +f_2 \cdot (s+1)$ is secure

We define the polynomials $r, f_1,f_2,s \in R[x]$. Where $r$ is a random degree 1 polynomial and $s$ is a random polynomial such that: $degree(s)=degree(f_1)=degree(f_2)$, let $R$ be $\mathbb{Z}_p$ ...
0
votes
1answer
67 views

AES - Encrypting multiple blocks of files

On my site, users can download files which are stored on public hosting, so I need to encrypt them. A downloaded file is divided into blocks of 1 kB and I want encrypt them individually, using the ...
0
votes
0answers
24 views

homomorphic paillier cryptosystem vs Elliptic curve cryptosystem

what are the pros and cons of homomorphic paillier cryptosystem compare to Elliptic curve cryptosystem??
1
vote
0answers
49 views

Modes of encryption for hard drives?

What are the currently recommended modes of encryption for large disks? Basic requirements would seem to be that you can update an encrypted sector independently of others, which rules out most ...
0
votes
1answer
80 views

Where have all the cypherpunks gone?

In 1992, cypherpunks was created as a mailing list for activists advocating for cryptography. Arguably, the cypherpunks mailing list was the foundation for the movement and the centre of it all. ...
0
votes
1answer
40 views

Simple encoding function mapping integers [on hold]

I am trying to analyse the following function. From an integer inputs it generates a series of 5 numbers. When looking at the some valid samples, clearly I can recognize some patterns (42 is ...
0
votes
1answer
66 views

DHE key exchange. Is it really secure?

Context I recently came across a video on the net showing the process of key exchange in Diffie Hellmann. Alice and Bob want to communicate. Eve is the (wo)man in the middle. This video is the ...
0
votes
0answers
22 views

Should I use a key store to keep my symmetric keys

I'm maintaining an application which handles several keys to encrypt/decrypt information. Some keys are used to encrypt text (user passwords, some sensitive data in the db, etc). Some other keys are ...
0
votes
1answer
42 views

Java: How to handle authenticated encryption for big files

First I need to mention that I can't use BouncyCastle to implement this solution. I have to encrypt files into the file system. Those files are not going to be tranfered over the wire to any other ...
1
vote
2answers
81 views

Encryption of big files in Java with AES/GCM

I have to encrypt big files. Say their size ranges from 500mb to several of gigabytes. I would like to use AES/GCM/NoPadding as provided by Java 1.8 since that gives me automatic authentication and ...
0
votes
0answers
19 views

if using cbc+hmac dealing with small size of data(less than 128bit) , will it cause any problem?

if use AES-cbc,HMAC-SHA256, and there is some txt needed to be enc, and I divide this txt into small packages with variable length, then enc them. some of these package can be less than 128bit. Is ...
0
votes
1answer
37 views

What happens when cbc+hmac get a replay attack?

If it use AES-CBC and HMAC-SHA256 for message send online, and someone try to replay attack on this message. Can the attack be successful? what will be happen when attacking?
1
vote
1answer
37 views

Is the output of AES-CBC + MAC the same size as the input?

I use AES-CBC and HMAC-SHA256 to encrypt a text file. Will the output be larger in size than the input or will it be the same size? Is it more secure secure if the size of the output is larger?
2
votes
1answer
40 views

Do data-dependent rotations have any advantage over fixed rotations?

There are many ARX ciphers, however most use fixed rotations. I know data-dependent compared to fixed rotations are: patented harder to implement constant time more expensive in hardware harder to ...
2
votes
2answers
157 views

Is there a way to systematically calculate the public exponent $e$ in RSA?

I'm learning RSA in one of my classes and we were given a problem: $p = 5$, $q = 11$ I have done the following steps: $n = 5 \cdot 11 = 55$ $\phi = (5-1)\cdot(11-1) = 40$ I know that to ...
0
votes
0answers
28 views

Elliptic curve trapdoor function without modular arithmetic?

From what I understand, an elliptic contains a set points satisfying the equation $y^2=x^3 + ax + b$ together with the point at infity. It seems clear how multiplication with a scalar and a point ...
0
votes
0answers
33 views

How many characters per block in an El Gamal ECC cryptosystem?

While I look for how many characters that can be encrypted using the The elliptic curve ElGamal cryptosystem. of each block found for these lines. But I can not understand Actually in our case we ...
-1
votes
0answers
42 views

Which Encryption Method is used for this stream cipher? [on hold]

Plaintext: 378734493671000 Encrypted: +VZyZlAHP6HAgoaPBrBz +VZ is common on all data there, so encrypted data might be yZlAHP6HAgoaPBrBz I think this is stream cipher? Could anyone tell me which ...
0
votes
0answers
27 views

Find the encryption method from the cipher and plaintext [on hold]

I have been given iogdaybDfD which is a cipher of the word narcolepsy. I need to find the type of encryption that has been applied to narcolepsy to encrypt it to iogdaybDfD. Could anyone advise on how ...
0
votes
0answers
17 views

CP-ABE: structure of the secret key SK

I am working on Ciphertext-Policy Attribute based Encryption (CP-ABE) and I need to understand how a secret key looks like. For example, assume that the universe of attributes is defined to be ...
0
votes
0answers
39 views

Interactive assumptions not falsifiable?

Can someone explain why an interactive assumption is not falsifiable? Maybe I'm misunderstanding what the statement means, but isn't even a non-interactive assumption interactive, but just with a zero ...
0
votes
0answers
21 views

Java RSA/ECB/PKCS1Padding encryption with .NET [on hold]

I need to encrypt a password on a web site developped in .NET using a public key. The public key is delivered through a Java web service with the information: The key is a RSA key to be used with ...
5
votes
0answers
66 views

Malicious DH groups

Can an attacker construct a DH group, large enough to be considered secure (say, a modulus of 2048-bits), such that the group appears safe, but the attacker is able to solve the DLP in the group ...

15 30 50 per page