# All Questions

2answers
416 views

### Is splitting AES ecrypted data safe?

Say I have a key, an iv and an AES/GCM/NoPadding encoded string and I want to split this information between three people such that only jointly can they reveal the ...
1answer
145 views

### On the privacy of perfect hash functions

I'm digging into the several algorithms for building (Minimal) Perfect Hash Functions. It seems that the recent works provide quite a few very efficient algorithms. However, I'm wondering how a (M)...
2answers
90 views

### linear computations over bilinear pairings

Does this hold in asymetric bilinear pairings? $e(x_1,x_2)e(x_3,x_4) = e(x_1x_3,x_2x_4)$, where $x_1,x_3 \in \mathbb{G}_1$ and $x_2,x_4 \in \mathbb{G}_2$ for a bilinear pairing $e$
2answers
130 views

### Three different numbers with x³=x mod p

p is a prime greater than 2 and $a \in \mathbb{Z}_p$. Why are there exactly three solutions for a³ = a mod p? Obviously 0 and 1 are both in $\mathbb{Z}$ and valid solutions, but that still means, ...
3answers
3k views

### How to calculate Modulo using a standard calculator for a one time pad encryption

I wrote a simple python script to preform one time pad encryption I would like to be able to decrypt the ciphertext by hand. In my script I use mod 26. This is how I was shown to calculate a mod ...
3answers
355 views

### What is h in this RSA variant?

I am trying to implement a proposed improved algorithm of RSA . Here the author has increased the number of exponents. However I am unable to understand what $h$ is in the Key generation step. Can ...
4answers
3k views

### How does TLS generate the shared secret?

From many readings, I got to know that TLS generates master shared secrets using pre-master keys and uses the DH algorithm to generate the shared secret/Master secret. What values during the hello ...
1answer
1k views

### Pollard’s Rho Method

I can't get my head around Pollard’s Rho Method for solving discrate log problem I have read in a book: The basic idea is to pseudorandomly generate group elements of the form α^i · β^j ...
2answers
105 views

### What is the difference between PPE and SPPE?

Can somebody explain, in simple terms, the difference between Pseudo Random Permutation Ensemble and Super Pseudo Random Permutation Ensemble?
2answers
1k views

### Is it possible to subtract/multiply numbers using homomorphic encryption?

Most of the libraries I've seen allow you to add encrypted numbers. Is it possible to subtract and multiply them?
3answers
244 views

### Which area of Maths should I pursue?

I would like to know which area of Mathematics would be most beneficial to cryptography. Surely Algebraic Number Theory and maybe to a lesser extend, Elliptic Curves, are closely linked to ...
2answers
200 views

### Does collision resistance stay when extending a hash function to a set domain?

Given a Cryptographic hash function $h$ for element $x$, let's extend it to sets via $H(S)=\prod_{x\in{S}}{h(x)}$. I am asking if the new hash $H$ (in domain of set) is still collision resistant? To ...
2answers
1k views

### Generate fixed length cipher text from arbitrary length plaintext

Using an encryption algorithm like AES, is it possible to generate a fixed length cipher text no matter how long the plain text becomes?
3answers
2k views

### Implementing secret reconstruction in Shamir's Secret Sharing

I am trying to implement Shamir's secret sharing in C++. I have got the generation of shares working. However, I am very confused with the reconstruction of shares. I get the part on how three users ...
2answers
194 views

### Do I need to know the “mode of operation” to decrypt a message encrypted with a block cipher?

If I have received an AES encrypted message, and if I do know the key with which it was encrypted, do I also need to know the mode of operation with which it was encrypted in order to decrypt it? My ...
1answer
221 views

### What does modular inversion mean?

I'm trying to implement an e-voting algorithm, which is described at the paper "Internet Voting Protocol Based on Improved Implicit Security" by Abhishek Parakh & Subhash Kak. At the Example 1 ...
2answers
122 views

### What can a master password also be called?

When having a company computer that is full disk encrypted, it is common that the boss have a master password / backdoor, so the data always can be decrypted. I have heard some call this for "scrow" ...
1answer
101 views

### Initialization value (IV) bit error

When a bit error happens in an IV, what would the result of decrypting a cipher-text be in the different encryption modes like ECB, CBC, CFB, OFB, and CTR?
2answers
89 views

### find solutions that solve the equations

I am implementing a timing attack on RSA for school and I need to generate two sets of messages $Y$ and $Z$ for which holds: $(Y^d \mod N) \cdot Y < N$ and $(Z^d \mod N) \cdot Z > N$ where ...
3answers
2k views

### Is it possible to use the RSA algorithm, or a variant, for software licensing?

I'm almost a newbie about RSA encryption, so my question could it be banal. I'm beginning to create a licensing system for my software. I need to distribute a crypted license file to many customers. I ...
2answers
529 views

### Complexity of ECB and OFB

What is the complexity of ECB in terms of Time and Memory? and also in OFB? I can't find it in the internet, so I decided to ask it in here.
2answers
215 views

### CPA distinguisher for matrix multiplication in GF(256) with randomized padding

What is the best CPA distinguisher for the function $F_k:\{0,1\}^{8n}\to\{0,1\}^{16n}$ described below? Let $E_k$ be a $2n\times2n$ matrix with elements in $GF(2^8)$, selected by generating bit ...
1answer
324 views

### BigInteger in Java and Randomness

I'm looking for some PRNGs and – as I have been using Java for a long period of time – I thought that the BitInteger class, together with the ...
2answers
2k views

### suggestions for cryptography projects for an ece 3rd year student

I am an electronics and communication engg student currently doing my 3rd year second semester. i am interested in info coding and the security aspects of it. As an ECE student i want to know what is ...
1answer
637 views

### Creating a hash of XOR'd blocks

Suppose a message $m$ is divided into blocks of length $160$ bits: $m > = M_1 || M_2 || ... || M_l$ And define $h(m) = M_1 \oplus M_2 \oplus ... \oplus M_l$ Which of the three desirable ...
2answers
88 views

### How to break a 32 bit block cipher without key?

From what I know Skip32 is the only 32 bit block cipher and I heard its not secure. What do I do or which tool do I use to break a 32-bit block cipher? I did search for this but all I find is attacks ...
1answer
84 views

### Analysis of DGHV Security

I want to know how security of DGHV can be breached using oracle and Binary GCD. As I study this paper : Fully Homomorphic Encryption over the Integers But I am not able to understand Section 4.1: ...
1answer
36 views

### Would A5/1 with a much larger state be a good choice of stream cipher for hardware?

Would A5/1 with a much larger state be a good choice of stream cipher for hardware? Assume that a reasonable choice of MAC is made such as GMAC, with the first 128 bits of the stream cipher output ...
1answer
126 views

### What is the difference between discrete logarithm and logarithm? [closed]

Why discrete logarithm? Is discrete logarithm is part of logarithm? I do not understand the difference between these two concepts.
1answer
94 views

### Really simple RSA style public private key generator

I am giving a talk to high school students and would love to do a real life encryption/decryption demonstration. I am not too familiar with the maths but is it possible to create like a 5-10 bit ...
2answers
87 views

### How to calculate entropy of output of a PRNG

Suppose the entropy of seed key is $H(n)$ which is $n$-bit long and random and the output bit length of the PRNG is $2^n$, which will be used as a long running key. Though it is obvious in that case, ...
1answer
66 views

### Running time of Shamir's secret sharing scheme

Let $p>n$ be a prime number. The key steps in the $(t,n)$ Shamir's secret sharing is as follows: Steps of dealer: Choosing $s \in \mathbb{Z}_p^*$ Selecting $b_i \in \mathbb{Z}_p^*$ for ...
1answer
67 views

### Hash + Salt v. Hash + Encryption

I was wondering if using a salt with a hash is more effective than hashing and encrypting your hash.
2answers
130 views

### Why can't NORX produce intermediate auth tags like Keyak can?

Why can't NORX produce intermediate auth tags like Keyak can? Keyak appears quite attractive because of this, but seems to be slow in the absence of hardware acceleration.
3answers
141 views

### Is multiplicative blinding less secure than additive?

It's easy to see that additive blinding (e.g., $x+r$ for secret x and random r) is perfectly secure in a finite field (this is a one-time-pad) and statistically secure for $r$ uniformly distributed in ...
1answer
122 views

### Why does image size increase after steganography?

I am working on a steganography technique. Sometimes I need to send my steganographed images online to my friends but in the process the image gets compressed destroying all the data. I found ways to ...
1answer
52 views

### Computing the cardinality of the co-domain of specific modular exponentiations

Consider the following function: $f: \mathbb{Z}_n \rightarrow Y,~x \mapsto x^e \bmod n$, where $n = p \cdot q$ is an RSA modulus and $gcd(\varphi(n),e) \neq 1$ (different as required for a public ...
2answers
156 views

### AES key equal to IV (CBC mode)

Application uses AES in CBC mode with 128 bit key. In this implementation key is always same and is equal to IV. Can attacker get the key or decrypt data? If he knows: First and second blocks of ...
2answers
265 views

### Certificate Signature Algorithm differs from Signature Algorithm Negotiated for Connection

With the upcoming sunsetting of SHA-1 by browsers I was checking signature algorithms for sites I visit. I'm using Firefox 43.0.2 on Windows. I noticed something interesting when I visited the site ...
2answers
190 views

### How can I use the whole potential of DES?

I have recently programmed the DES algorithm. Right now it works just with integers (or better to say chars) in the range <0;255>. How can I use its whole potential - using just ASCII would be a ...
1answer
111 views

### Why is RSA encryption version 1.0 not specified in an RFC?

I saw that there are three RSA encryption versions, as follows: RSA encryption version 1.5 (RFC 2313) RSA cryptography specification version 2.0 (RFC 2347) RSA cryptography specification version 2.1 ...
2answers
63 views

### Can several run of a semi-honest protocol be used to infer malicious security?

In the ideal world, $A$ sends several inputs $x_1,...,x_\lambda$ to the functionality and $B$ sends input $y$. Functionality sends $f(x_1,y),...,f(x_\lambda,y)$ to $A$ and nothing to $B$. Suppose ...
2answers
206 views

### Parity of an encrypted key

Does encrypting a double-length 3DES application key (that has an odd parity) under a double-length 3DES zone master key (also with an odd parity) affect the parity of the application key?
1answer
127 views

### Algorithm to transform plaintext to a key of desired keysize, when using input plaintext as key for FPE?

Using a format preserving encryption scheme that uses AES internally as its block cipher, for a plaintext that I encrypt I want to use that input plaintext as the key. However using AES-128, my ...
2answers
120 views

### What is the meaning of probabilistic encryption algorithm?

I am learning cryptography by myself and I am not able to understand the meaning of probabilistic encryption algorithms. How is it different from deterministic encryption algorithms ? How can the ...
1answer
179 views

### Is there a way to encrypt an integer within an arbitrary range?

I need an algorithm that can take an integer, an arbitrary range, a key of 16/24/32 bytes, and an initialization vector of 16 bytes(ideally), and return an integer in the same range. My latest attempt ...
1answer
44 views

### Security of a signature scheme based on both factoring and discrete logarithms

I have seen this paper: A New Signature Scheme Based on Multiple Hard Number Theoretic Problems by Ismail and Tahat: In this paper, we propose a new signature scheme based on two hard number ...
2answers
311 views

### Basic Encryption and Decryption related question

I recently started studying cryptography and got interested in the subject. But I got this doubt when I was studying the encryption scheme. Even though we encrypt our message and change it into ...
2answers
121 views

### Which data encryption mechanism to use for data transfer?

I have high performance nodes communicating with each other sending logs and data over network. The communication is heavy and over public network. I would like to know how to know which is the best ...
2answers
175 views

### What are the required security properties for salts?

I was recently thinking about password hashing (maybe caused by the PHC progression). I started to think a little more about it and got stuck at this question: What security properties do password-...

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