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 ...

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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 $...
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4answers
117 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?
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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', then ...
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1answer
303 views

One cipher to rule them all?

I learned from Dan Boneh's course that many cryptographic primitives (prngs, stream ciphers, hashes, hmac, key derivation functions) can be built from just one a block cipher or PRF. For example, the ...
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39 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.
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2answers
116 views

Homomorphic Encryption with Addition and Exponentiation

Is there any homomorphic encryption scheme which supports addition and power over cipher text ? Paillier is close but it supports addition and multiplication with a constant. I am getting an output ...
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900 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: $\operatorname{CRC}(a) \oplus \operatorname{CRC}(b) = \operatorname{CRC}(a \oplus b)$ ...
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1answer
122 views

Big block cipher as memory-hard function

I'm wondering, if something like block cipher with big block size is a good memory-hard function? All memory-hard key derivation functions I've seen look more complex than that, which made me ...
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47 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 constants....
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1answer
49 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 ...
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2answers
155 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 square ...
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2answers
187 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 ...
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1answer
130 views

Image sharing without data overhead

The idea is to share $n$ images among $n$ persons so that all images can be reconstructed by someone in possession of all shares. However, there must not be any data overhead (which means the shares ...
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19 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 ...
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0answers
29 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 ...
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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, ...
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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 ...
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1answer
97 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 ...
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63 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 ...
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0answers
70 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?
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1answer
53 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. ...
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2answers
77 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 example;...
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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, ...
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1answer
70 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 ...
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46 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 ...
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4answers
3k views

Does encrypting twice using the same block cipher produce a security weakness?

If I use the output of a cipher, for example a block cipher such as AES and encrypt it again with the same algorithm, I read that this introduces weaknesses into the overall security of the system. ...
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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 ...
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1answer
57 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 authenticity/...
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2answers
420 views

What operations are used in symmetric cryptography and why?

In continuation to Why are bitwise rotations used in cryptography?: what other operations are commonly used in symmetric cryptography? Are there particular operations on numbers that are good for ...
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1answer
82 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 ...
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1answer
39 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 ...
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0answers
58 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 ...
2
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1answer
146 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, ...
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2answers
353 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 ...
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1answer
28 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 ...
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1answer
104 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.
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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? ...
3
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1answer
101 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 ...
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2answers
171 views

Advantages of making streamcipher stream depend on plaintext?

Most descriptions that explain how streamciphers work (like the one on Wikipedia), tend to describe a model that boils down to a simple “$ciphertext = plaintext \oplus stream$”, where the stream is ...
4
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2answers
126 views

Is there such a thing as a hash function with a fixed size input?

That seems like it would be a useful primitive. Using it in place of a block cipher in the Merkle–Damgård construction would give a variable-length hash, maybe without the tricky business with related ...
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3answers
176 views

How to convert RSA public keys to one key to use for text hashing?

I've recently asked a question about RSA encryption. One of the things that I don't understand is the usage of two public keys. In the example on Wikipedia, a message is encrypted like: ...
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0answers
121 views

Homogenous and heterogeneous Unbalanced Feistel Networks

Unbalanced Feistel networks can be homogenous (F-function identical in each round), or they can be heterogeneous (F-function not always identical in each round). The advantage of heterogeneous UFNs ...
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4answers
720 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: ...
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2answers
225 views

Is there an algorithm to hide text in another text, while preserving the meaning of the latter?

Is there a way to hide a text message $A$ inside another text $B$ using a cryptographic cipher/algorithm, while preserving the sense/meaning of $B$ and without anybody being able to notice there is a ...
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0answers
69 views

What can I do to improve my encyption method [closed]

I'm new to cryptography and I want to learn more. For me, the best way to learn about something that I have no experience with is to experiment and I've coded a very basic approach to a simple ...
0
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1answer
213 views

Self-Convergent Hashing

What is the name of an algorithm that hashes its result as an embed of larger set of data that results back to the hash? For instance where $f(x)$ is the hashed result and $x$ is the dataset, and $f(...
4
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0answers
84 views

Adding parameters to sponge's capacity

Is it safe to XOR parameters like domain, length of the message or block counter into sponge's capacity or that gives attacker control over capacity? For example NORX XORs domain into capacity. Does ...
3
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1answer
590 views

How to prove that a function is not pseudorandom?

I am currently enrolled in a cryptography course, which uses the book by Katz and Lindell. I'm struggling with the exercies which ask for proofs, like the following one: Let G(k) be a PRG with |k|...
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1answer
235 views

What is the difference between key size and block size (for AES)

We are working on AES and want to develop a website which should provide an encryption facility but we are not understanding the difference between key and the block size. More appropriately what does ...
3
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1answer
144 views

Theoretical decryption of RSA

I am currently looking into RSA and have some questions. I am interested in theoretical answers, assuming there is infinite time for decryption. Is it necessary to work out the private-key exponent ...