1
vote
1answer
412 views

Elliptical curve cryptography key generation time

I am currently trying to learn more about Elliptical curve crypthography and have finally started to get things working and undestanding the different pieces. I've written a small project in C# and ...
1
vote
2answers
393 views

Sharing an encrypted file between a group of people

Is there any way to share an encrypted file with a group? In the other words, can I encrypt a file with a public key so that each person in a group decrypt it with his/her private key? Is there any ...
1
vote
1answer
89 views

simulating rc4-256 with rc4-128

OpenSSL supports rc4 with 128-bit keys and rc4 with 40-bit keys. It does not support rc4 with 256-bit keys. My question is... is it possible to modify the state of the pseudo-random generation ...
2
votes
1answer
129 views

what are multi-primes and how are they different from semiprimes?

I came to know of semiprimes recently. The simplest explanation of semiprimes is you take any two prime numbers and you multiply them, say 3*11 = 33 in which case 33 would be a semiprime. The numbers ...
-2
votes
2answers
271 views

Cracking plain RSA by factoring the modulus n

This is the setup: I have both public and private keys of one "instance" of RSA. And I have only the public key of another RSA cryptosystem, but this system has the same modulus as the first one. I ...
0
votes
2answers
163 views

Where to store the file extension to retrieve it correctly after decryption

I am using Java to write AES-256 to encrypt various files with different extension, the problem is, where am I suppose to store the file extension so the if the data is decrypted, the file extension ...
1
vote
0answers
90 views

Less known hash functions producing 128 bit hash [closed]

Good day. While reversing a malware I stumbled upon a function producing 16 byte hash. I tried to determine which one is that by checking every function from wiki. Nothing fits. So, there are two ...
1
vote
0answers
78 views

Efficient proof of knowledge using Wegman-Carter hash

A verifier wants to ensure, with only little exchange of data with other systems, that a large block of data $M$ that the verifier holds is also available to some other system(s). It is not an ...
0
votes
1answer
83 views

Inverse of a function $f_k(x) := f (x ⊕ k) ⊕ k$

$f : \{0, 1\}^4 → \{0, 1\}^4$ Given a function $f_k(x) := f (x ⊕ k) ⊕ k$, what is the inverse function $f_k^{-1}$? I could not figure out how this would be done. Thanks.
-1
votes
1answer
122 views

El gamal correctness

I tried to find online for the correctness of El-Gamal, but I couldn't find any good resource that will teach me how to show the correctness of El-Gamal, could any body show me how is it done?
2
votes
0answers
103 views

Recovering El Gamal secret key from signatures [duplicate]

Assume out of a set of ElGamal signatures, I've discovered that two have the same y i.e. $signature_{1}$ on $m_{1}$ = $(y,s_{1})$ and $signature_{2}$ on $m_{2}$ = $(y,s_{2})$. The public keys for ...
1
vote
1answer
95 views

What is the difference between IND-CCA2 and NM-CCA2? And how does one imply another? [closed]

Is there any proof that shows the equivalence of these two?
1
vote
1answer
173 views

Building a pad for OTP on-the-fly with Diffie-Hellman

Through repeated DH attempts, could Alice and Bob build a large random key for use as a one-time pad? My intuition is that this protocol would be as hard as breaking DH (discrete logarithm).
2
votes
1answer
144 views

Private Information Retrieval--Is it still theoretical?

Are there any real world products in which private information retrieval techniques are used?(a data hosting server oblivious of which data item was fetched from it?)If not what are the major barriers ...
1
vote
0answers
225 views

Recover a secret message in a .wav file [closed]

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 ...
-1
votes
1answer
438 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.
3
votes
2answers
276 views

Real life systems that use concepts of crypto computing [closed]

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
223 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
1answer
430 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 ...
2
votes
1answer
167 views

Gap problem for Learning With Errors

Informally, a "Gap problem" arises when solving the computational (or search) version using an oracle for the decisional version. This definition of Gap Problem was introduced by Okamoto and ...
3
votes
2answers
179 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 ...
1
vote
0answers
137 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: ...
1
vote
1answer
2k 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
41 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
vote
1answer
461 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
131 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
168 views

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

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. $a, b$: ...
7
votes
0answers
180 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
131 views

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

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
152 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 ...
1
vote
2answers
240 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 ...
2
votes
1answer
97 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 ...
2
votes
1answer
111 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
155 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 ...
3
votes
1answer
161 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 ...
1
vote
1answer
142 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
2answers
209 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 ...
1
vote
1answer
766 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 ...
4
votes
2answers
3k 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
1answer
49 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
151 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
266 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?
3
votes
1answer
156 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
337 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
85 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
1answer
117 views

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

Looking for the number of characters that can be encrypted using the The elliptic curve ElGamal cryptosystem of each block, I found these lines. But I cannot understand them: Actually in our case ...
0
votes
0answers
153 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 ...
1
vote
0answers
143 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 ...
7
votes
1answer
179 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 ...
0
votes
1answer
66 views

special public keys and modulo n

I just picked up cryptography and have some questions on RSA cryptosystem: Say there are two public keys (n, e1), (n, e2), e1 is coprime to e2. They share the same n. Is it possible to find the ...

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