Design of cryptographic primitives (algorithms), like block ciphers, stream ciphers, random-number generators, hash functions, MACs, key exchanges, public-key encryption or signature schemes. Also tag with the relevant type of primitive. If you ask about a known existing algorithm, also tag with its ...

learn more… | top users | synonyms (1)

1
vote
0answers
34 views

Issue Factorization Quadratic Sieve

Good evening, I'm about to write my own quadratic sieve implementation in C using GMP library for large numbers. I'm facing an issue while attempting to do the last factorization step for the number: ...
9
votes
1answer
70 views

Collisions in the cyclotomic knapsack function

I've been working my way through the paper “Efficient Collision-Resistant Hashing from Worst-Case Assumptions on Cyclic Lattices” by Peikert and Rosen, and I've come across something that doesn't seem ...
-2
votes
0answers
30 views

How do Galios fields work in AES? [duplicate]

I am trying to learn how AES functions but I keep hanging at the subject of Galios fields. I am reading a lot about them but I just can not find an understandable explaination in how they work. Could ...
1
vote
1answer
47 views

Expire signature

I am looking for a way to have a 'did it expired' key. There's a similar question here, but I have to prevent reusing of the 'did it expired' signature . A possible solution would be a two one-way ...
2
votes
0answers
25 views

Security of randomized data dependant key schedules?

An example to demonstrate the point with two Feistel networks: Cipher A: \begin{align} roundkey = hash(key || counter)\\ roundkey = hash(key || roundkey)\\ left = left\oplus hash(roundkey || ...
1
vote
2answers
27 views

Validating subset of a password

Is anyone aware of an algorithm/method that allows me to validate just a few letters (or other characters) from a password. For example, the application asks for the 2nd, 3rd, 6th and 9th letters from ...
1
vote
0answers
54 views

Is it safe to encrypt data using XOR along with CSPRNG seeded with a truly random number? [closed]

I was wondering a couple of days ago whether I could reverse the normal encryption order to produce a good AES based cipher variant. The method is as follows: Two users, Alice and Bob, each have a ...
3
votes
1answer
67 views

How are boolean functions used in cryptography?

I recently started becoming interested in Boolean functions. Because they are defined as $f: \{0, 1\}^n \rightarrow \{0, 1\}$, or in other words only over $\{0, 1\}$, I guessed they can somehow be ...
1
vote
0answers
48 views

Given a public-key encryption and signature scheme, define a new primitive

I'm new to cryptography and am currently working on the following question: Say you are given a public-key encryption scheme $\Pi_e=(\mathcal{K}_e,\mathcal{E},\mathcal{D})$ and a signature scheme ...
0
votes
1answer
72 views

Inverting RSA using an oracle

Say you are given an efficient deterministic algorithm 'I' that can invert the RSA function on 1% of the points in $Z^*_{N}$. That is to say that if y $ \in $ $Z^*_{N}$ is a "good" point for 'I', ...
9
votes
2answers
2k views

Why is the permutation in AES (and other ciphers) not random or key-dependent?

If the permutation in AES (or other ciphers) were randomly generated or dependent on the key, would it not be stronger against differential attacks? If this is so, then might we need fewer rounds for ...
0
votes
1answer
46 views

Secret construction

Given set of random strings $w =\{s_1, s_2, s_3 ... s_n\}$ are there any algorithms to construct single master secret $S$ from them? Subsequently we should be able to deconstruct the $S$ back to ...
1
vote
0answers
36 views

How to encrypt an image with logistic chaotic map?

I need to encrypt color images, using logistic chaotic map. Could you please recommend an algorithm for this? All the articles that I've found on the Internet are completely unclear.
6
votes
1answer
81 views

Calculation of the avalanche effect coefficient

Given a strict avalanche criterion matrix/dependence matrix for a hash function,how do I calculate the avalanche coefficient for it. I want to calculate a single parameter(value) which represents the ...
3
votes
0answers
41 views

Can an analog of ChaCha with 64-bit words be defined, and would it be secure?

Blake2b has a lightning fast compression function with more-than-overkill security even against quantum attacks. It seems to be based on ChaCha, but with 64-bit words and different rotation ...
1
vote
2answers
71 views

Factoring large $N$ given oracle to find square roots modulo $N$

When $p$ and $q$ are distinct odd primes and $N = pq$, the points in $\mathbb Z_N^\ast$ have either zero or four square roots. A quarter of the points have four square roots; the rest have no ...
11
votes
2answers
885 views

Why is CRC said to be linear?

It is commonly understood that CRC satisfies the linear identity with respect to the $\oplus$ (XOR) operation: $\operatorname{CRC}(a) \oplus \operatorname{CRC}(b) = \operatorname{CRC}(a \oplus b)$ ...
4
votes
1answer
45 views

Could a strong round function be immune to slide attacks

An excerpt from the wikipedia article on slide attacks states: ...The only requirements for a slide attack to work on a cipher is that it can be broken down into multiple rounds of an identical F ...
3
votes
0answers
89 views

Finding sum of two encrypted numbers

Let's consider such process: Two emitents emit two (integer) secret numbers independently They encrypt (encode) these number in such a way that no-one (except emitent) can decode these numbers. ...
4
votes
2answers
186 views

Should I use a self-designed Block Cipher Mode of Operation?

We all know we should NOT roll our self-designed encryption algorithm, how about block cipher mode with a certificated cipher method like AES? Will a self-designed block cipher mode cause any flaws or ...
3
votes
0answers
17 views

security of Even-Mansour scheme with keyed shuffle

I was researching the Even-Mansour scheme and had a question that wasn't addressed in the paper that I saw, and google was minimally helpful. What if a permutation that uses secret data like the ...
3
votes
0answers
28 views

Publishing only items your subscriber previously subscribed to, without you knowing which those items are

Let's say you were given a dump from a security breach. You want to share the email addresses affected by the breach with a separate company who pays you for this service so that they can protect ...
0
votes
0answers
16 views

Implications of pattern in finial digit of prime numbers [duplicate]

http://qz.com/639452/mathematicians-are-geeking-out-about-a-bizarre-discovery-in-prime-numbers/ What are the implications of this (very) new research on crytopgraphy? I would have thought this would ...
16
votes
2answers
2k views

Why is Pearson hash not used as a cryptographic hash?

The original algorithm produces 1 byte long hash and is (of course) not suitable for cryptography use. But according to wikipedia, it is possible and easy to produce Pearson hash of any length, ...
0
votes
1answer
41 views

Sum of digits flaw name request

Let's say I am making an encryption algorithm, and in the algorithm in have the following step: "multiply the integer from the previous step by 9 and take the sum of the digits of the resulting ...
3
votes
1answer
71 views

Why inversion and multiplication operations are costly in elliptic curves?

There are several algorithms for efficient scalar multiplication of an arbitrary point P(x,y) by some positive integer k in elliptic curves defined over $F_{p}$ or $F_{2^{m}}$. The scalar ...
1
vote
4answers
110 views

Do any cryptography algorithms work on numbers besides primes?

I know prime numbers are important for several algorithms and protocols. Are there any algorithms and protocols that don't require primes?
1
vote
0answers
56 views

Encryption & decryption of integers using modular multiplicative inverse and extended euclidean algorithm

I'm looking for a neat algorithm, which is capable of encrypting an integer to another integer and decrypting it again AND is secure. When I was in university, my professor showed me an awesome way ...
1
vote
0answers
54 views

Fast algorithm for reduction modulo a prime [closed]

If the prime is $p=2^a\cdot3^b+1$ , is there any fast reduction technique modulo this prime?
3
votes
1answer
48 views

Bitwise operation question with shifting involved

I am trying to find a value of X (32 bits) such that ((X XOR a)+b)<<3 = (X+c) XOR d. <<3 means shift left 3 bits. a,b,c and d are all constants which have been determined elsewhere. ...
3
votes
2answers
58 views

Non primitive lfsr sequence

Given a non-primitive LFSR sequence (i.e number of states is less than $2^n - 1$); how do we find out the the characteristic polynomial? Will Berlekamp-Massey algorithm work in this case? for ...
2
votes
1answer
64 views

Distinguishing two sets of pseudorandom values when their keys differ by one

Suppose we use a pseudorandom function $PRF$ and a random key $k$ to generate a set of pseudorandom values: $\forall i, 1\leq i \leq n: w_i=PRF(k,i)$ Now, consider instead of picking a fresh key, ...
2
votes
1answer
177 views

How is a per round key generated in DES algorithm?

I am reading over a slide that I found online regarding the DES algorithm for encryption and I am a little confused about the per round key generation. From the slide below, I understand that each per ...
3
votes
0answers
42 views

How to make a “zero knowledge” cache/key-value store

I'd like to use a possibly insecure cache for storing expensive-to-calculate sensitive information. My requirements are: If the cache ever gets compromised it should reveal nothing about its ids or ...
0
votes
1answer
51 views

Difference between HMAC-SHA1(key, msg) vs SHA1(key + msg) [duplicate]

Is there any practical difference from using HMAC-SHA1(key, msg) vs SHA1(key + msg) as a way to verify the ...
24
votes
4answers
3k views

Are checksums essentially non-secure versions of cryptographic hashes?

Are checksums basically toned-down versions of cryptographic hashes? As in: they are supposed to detect errors that occur naturally/randomly as opposed to being designed to prevent a knowledgeable ...
1
vote
1answer
36 views

Secure way to hash a lookup value

I want to securely store a database table that consists of an account ID and a few columns of sensitive data. The data only has value if it can be associated with the account ID. My thinking is to ...
0
votes
1answer
65 views

Are any public key algos commutative?

Are there any public key encryption algorithms that allows for arbitrary ordering of crypto operations (commutative). That is, given a plaintext "message1", the following operations work to doubly ...
0
votes
0answers
48 views

Simulation of a custom build network security algorithm with ElGamal Cryptosystem using Elliptic Curve

I am trying to build an algorithm to encrypt and decrypt text using ElGamal Cryptosystem using Elliptic Curve. My algorithm generation is done. But at simulation part I stuck. My algorithm steps are ...
3
votes
2answers
202 views

How to calculate key size of a security algorithm?

There are lots of security algorithms. One of the way to measure security of a cryptography algorithm is to find out its key size. There are many key size of a single algorithm. ECC (Elliptic ...
2
votes
1answer
132 views

Questions about a SHA3 cipher stream encryption scheme

I have written an encryption implementation using a hash as a cipherstream for demonstration purposes. I know it is slower than more sensible options such as AES but I am interested in several things, ...
0
votes
1answer
27 views

Vulnerabilities in specifying the hash algorithm used for signature verification on a per-message basis

Let's say that I have a 4096-bit RSA key and when I sign data, I typically use SHA-512. As far as I understand it, the hash algorithm used to sign/verify a message is specified in the message. If a ...
-1
votes
1answer
103 views

How to find roots of equation $f(x)=0 \pmod p $, where $p$ is prime number?

$f(x)$is any nth degree equation $n>0$, how to find roots of $f(x)$ over prime modulo.
0
votes
0answers
55 views

How do substution-permutation networks work? [duplicate]

I understand what is going on in higher level. But I don't understand what's really going on in page 3 and 4 of this slide. Specifically, How $S_0$ and $S_1$ is used? What goes in what goes out? ...
2
votes
1answer
79 views

Construction of division polynomials

I'm trying to understand the construction of the division polynomials used in Schoof's algorithm. I firstly followed this report of Charlap and Robbins. I stuck with the definition of the leading ...
3
votes
2answers
192 views

What is the difference between SHA-3(Keccak) and previous generation SHA algorithms?

SHA-1 and SHA-2 share the same structure and mathematical operation as their predecessors - SHA-0 and MD5. Both SHA-0 and MD5 have been broken. This is one of the main reasons why SHA-1 is considered ...
3
votes
1answer
92 views

How does RIPEMD160 pad the message?

For RIPEMD hashing algorithm on hardware I am not exactly getting how padding works So as per my understanding padding will work like explained below: For ripemd 160 message should be multiple of ...
5
votes
0answers
141 views

help with cryptanalysis of a sponge permutation

I have been studying and researching hash functions. So far my research has led me to the sponge construction. It appears that the permutation used in the sponge to stir the state is more or less ...
8
votes
4answers
656 views

Hashing a password before using for online accounts

I don't actually know what I'm talking about, so apologies if I get anything wrong. At the moment I have a password naming system for most of my online accounts that looks something like this: ...
5
votes
0answers
31 views

Understanding the definition of HGD

On the section 4.2, page 10, of the paper Order-Preserving Symmetric Encryption, the authors define two subroutines: the first one is called $HGD$ and the second one is $GetCoins$. I have doubts ...