Questions tagged [algorithm-design]

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 name.

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135 views

Security of AES under modification of Sboxes and/or MDS mixing layer

Is the security of AES algorithm increased by using many s boxes at the same time instead of using only one s box , and the same question for using many MDS instead of only one.
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1answer
105 views

Proof of Disclosure? Is there such a thing?

Let's say I have a document. I want to give you a copy, and then I want to prove that I gave you a copy. Ie, I want some kind of digitally signed receipt from you. If you're dishonest, you may receive ...
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1answer
172 views

Using non-standard constants for SHA-256

For SHA-256, FIPS 180-4 states the following on the constants: These words represent the first thirty-two bits of the fractional parts of the cube roots of the first sixty-four prime numbers. If ...
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1answer
266 views

AES: a question about dual ciphers and security

I have recently learned of dual ciphers, in particular dual ciphers of AES. It seems there are many. Most of my information comes from:(1) Representations and Rijndael Descriptions. In this paper the ...
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1answer
135 views

(AES in mind) How can we show two irreducible polynomials have a bit-wise linear isomorphism

This refers to answer 2 on a similar question:Design properties of the Rijndael finite field I am unsure what many of the terms mean in this answer. I think a bit-wise linear isomorphism of ...
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200 views

If we use another irreducible polynomial for AES how can we show it is still resistant to DCA and LCA?

AES has been rigorously tested against all known attacks. However, I believe there are 30 suitable irreducible polynomials that could be used for AES. If we were to change the current irreducible poly ...
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2answers
73 views

How to transform a text into numbers in the shortest way possible? [closed]

My challenge is to transform a text into a representation of numbers 0-9. The number representation has to be as short as possible. What are the best options to achieve this? Edit: I also need to ...
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2answers
71 views

How to combine AES-CMACs

I have a primitive that is able to generate a AES-128-CMAC from a message. $\operatorname{CMAC}(\text{MessageAddress}, \text{MessageLength}) \rightarrow \text{result}$ I cannot change this primitive....
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1answer
922 views

Cryptography math requirements [closed]

I know that most of the math related to cryptography is number theory/abstract algebra/probability, but I was wondering if there are some algorithms that make use of other fields of math like real/...
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4answers
13k views

Cryptography algorithms that take longer to solve on a GPU than a CPU

I know that Graphics cards are faster at solving algorithms like SHA-256 because of the many builtin processors, but are there Algorithms that take actually longer on a Graphics card than on a modern ...
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2answers
303 views

Homomorphic Encryption Arithmetic Operations [closed]

I am looking to do arithmetic operations on encrypted values that will decrypt to be the result of the value decrypted. Does anyone know of any code examples of this in use? Usage of the equation ...
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1answer
289 views

Is there an encryption algorithm with a key that can only be used to decrypt?

I was wondering if there were any encryption algorithms that kinda worked like RSA in the sense that there are two keys, however, one of the keys only decrypts (meaning you can't encrypt with it) and ...
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3answers
834 views

An unbreakable book cipher?

In a recent press interview, a former terrorist of the 1970s described the cipher his group used to communicate. He claimed that method was unbreakable and I wonder if cryptographers today would agree....
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What Is The Weakest Possible Encryption Algorithm [closed]

I've been creating a Capture The Flag site and for one of the challenges I wanted you to have to break an encryption algorithm. Granted I want it to be a weak one, so I want the weakest out there. One ...
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2answers
198 views

Is encryption possible without secure random numbers?

All cryptographic algorithms I know of that satisfy Kerckhoffs's principle rely upon secure random number generation. Assuming the existence of a 'numerical oracle' capable of perfectly predicting the ...
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1answer
219 views

Assuming that NP = RP, how would this impact cryptography?

In terms of complexity classes, we assume that NP = RP. In other words, we assume that there is a randomized algorithm that solves a NP complete problem (and through polynomial time reductions, ...
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1answer
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Confusion and Diffusion in the AES functions

I am pondering, how each of the four functions that a full AES round does consist of (Add Round Key, Substitute Bytes, Shift Rows and Mix Columns) add to the confusion and diffusion of the full AES. ...
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2answers
281 views

Suitable Symmetric Algorithm for Encryption

Please, I would like to encrypt word not more than 5 letters such as (GO, HI, APPLE, EYES) and my key length just (40 bits only), please I am looking for a suitable symmetric algorithm that it can be ...
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1answer
488 views

Is there such a thing as “Fast Hashing Algorithm”

Short version Is it possible to accelerate hashing process by computing several hashing together in a "smart" way? Long version It's generally true that the algorithm complexity of several problems ...
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4answers
604 views

How can an amateur introduce a cryptographic algorithm?

I have a new cipher, and I want to get it properly vetted, but I don't have a strong way to prove its security properties. I'm an amateur without ties to a strong cryptographer/university. I have ...
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2answers
801 views

Does a two-way fixed-length hash function exist?

Just wondering if a two-way fixed-length hash function exists. I'm not talking about encryption where your output is the same size if not larger than your input. I guess the best way I can put it is "...
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1answer
1k views

Primitive polynomials and irreducible polynomials? [closed]

This question may seem annoying to some scholars as it is a very silly question but as I am new on this topic, it seems quite confusing. All minimal polynomials or primitive polynomials are ...
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1answer
105 views

Are “deterrent” algorithms like NFS and Coppersmith's algorithm actually used in practice?

It seems like there are a lot of algorithms in number theory which I would classify as "deterrent" algorithms -- for example the various number field sieves for factoring, Coppersmith's algorithm for ...
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1answer
96 views

What are the “natural language input messages” that were used to derive Streebog's constants?

This is more "cryptography trivia" than proper cryptography, but I'm curious. In Note on Streebog constants origin, V. Rudskoy says that the constants used in the definition of the Streebog hash were ...
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3answers
194 views

Why are the right halves kept unchanged in Feistel networks?

As I'm going through the Feistel network in the DES algorithm. While encryption uses a Feistel Network, the input block is divided into two halves left ($L$) and right half ($R$). In each round, the ...
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1answer
67 views

What would be the most efficient way to find two large (2048bit) integers $k$ and $q$ such that $p = kq + 1$ is prime and so is $q$?

What would be the most efficient way to find two large (2048bit) integers $k$ and $q$ such that $p = kq + 1$ is prime and so is $q$? Is there some standard algorithm that I could use?
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1answer
265 views

Does the prime modulus have to be bigger that the generator?

In the DH algorithm $ a^x \bmod b $ where $ a $ is the generator and $b $ is the prime modulus does $b $ have to be bigger than $ a $ or could $ a $ be larger for example $ 19^x \bmod 17 $ . Because I ...
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1answer
192 views

Simple compression functions an sponge functions for educational purposes

For block ciphers, there are the very well designed schemes of Simple-DES and Simple-AES, which have been created not for security but for teaching the design principles of the real algorithms while ...
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2answers
144 views

Key vs Algorithm when applied to Enigma

I've just been reading the Why should I make my cipher public? question and answers on this site. I understand Kerckhoffs's principle, but I'm unsure exactly how this applies to Enigma - i.e. where ...
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1answer
150 views

Getting the Encryption Function From the Decryption Function + Decryption Key + Encrypted Item

Is it mathematically possible to always be able to get the encryption algorithm used to encrypt a certain item (file, number, text, ...etc.) by knowing the decryption algorithm that will be used to ...
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1answer
87 views

Online attendance system

This summer I have made a website for my school's NHS program and integrated it with google scripts to automate tasks such as accessing how many hours users have and to allow members to view how many ...
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Antshares (NEO) algorithm (dbft) - Vulnerability to attacks - Game theory

This is more a game theory question, I think that this Forum is the best for this question. Please also correct me at the following text if I write something wrong. I understand the consensus ...
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363 views

A novel encryption method using only a (huge) lookup table. Is this remotely secure? [closed]

So I've come up with an (admittedly impractical) encryption method using a lookup table. The table is a shuffled list of all unsigned 32-bit integers, effectively making it a 32-bit unkeyed PRP. I ...
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2answers
116 views

What is the purpose of the middle-man actor in chaffing and winnowing?

Chaffing and winnowing is presented as a form of confidentiality without using encryption. This is beneficial for countries where encryption is regulated. Below is a diagram from Wikipedia showing ...
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133 views

Is there a way of increasing the time to brute force a cipher, but by increasing the ciphertext size instead of the key size?

If you have a symmetric-key algorithm that is limited to using a small key size (say 40-bits) is there any way you could increase the resistance to brute force attacks without increasing the key size? ...
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726 views

Just how surjective is a cryptographic hash like SHA-1?

From “Are common cryptographic hashes bijective when hashing a single block of the same size as the output” and “How is injective, inverse, surjective & oneway related to cryptography”, it is ...
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Cryptographic Tagging of Information over an Insecure Channel

Is there an efficient algorithm for the tagging and location of information over an insecure channel, where two parties (the tagger and the intended recipient for the tag) can recognize a piece of ...
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1answer
312 views

Is $a b + e \mod P$ hard to invert?

Given $a, p$, $c$ where $c = a b + e \mod p$, can $e$ be recovered? Additional details: $p$ is prime $a, p$ are re-used across many instances of the problem $b, e$ (and by extension $c$) are always ...
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1answer
173 views

Double-CBC as AES-KW Substitute?

Background. I'm trying to make a local command-line based password manager. So far, I've managed to make the output look dizzy on tty, and I plan to encode user credentials in individual 512-byte ...
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1answer
275 views

How do fast multiplication algorithms deal with cryptanalysis?

Math algorithms like Karatsuba and derivatives - do they have any applications for cryptanalysis of asymmetric cryptography algorithms? What if we have very fast multiplier? How can it help with ...
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1answer
159 views

Understanding an encryption technique algorithm

I have trouble understanding steps for Key set generation mentioned in an article titled as "An optimized encryption technique using an arbitrary matrix with probabilistic encryption". The steps are: ...
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1answer
133 views

FHMQV-C \sigma calculation - Full Dual Exponential Challenge Response (FDCR) signature schemes-

I'm studying the protocol FHMQV - C but I don't understand how two honest parties can reach the same value of $\sigma$. The paper that I'm studying is: https://eprint.iacr.org/2009/408.pdf. If you ...
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1answer
63 views

Key generation algorithm based on bytes in a drive [closed]

I am a novice cyber security student and thought of a way to generate a random cryptographic key. The algorithm works as follows: Get the size (in bytes) of every file in a directory (drills down ...
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1answer
147 views

Average number of multiplications in left-to-right k-ary exponentiation

On page 617 in chapter 14 of The Handbook of Applied Cryptography, the average number of multiplications in left-to-right k-ary exponentiation is $ l\times (2^k-1)/2^k$, where $l=\lfloor t/k\rfloor $,...
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1answer
97 views

Looking for the inverse of the following equation

I am working on some image encryption algorithm and got stuck. I have plaintext data value of $256$ and perform the following (all values in decimal): $$[256 \oplus 2] mod (256) = 0$$ What will be ...
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1answer
275 views

Post-Quantum Primitives' Object Sizes

1. Alternative Cryptographic Primitives For quite a while, I've been thinking is it possible to "craft" a cryptographic primitive (like ECC) suitable for the purposes of post-quantum cryptography, ...
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1answer
1k views

Pollard's kangaroo attack on Elliptic Curve Groups

Let's say I've intercepted some bits of a Diffie-Hellman private key: $x = n \mod r$. I can get the remaining bits by doing a kangaroo search. This algorithm works over $\mathbb{F}_p$. Can it be ...
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3answers
323 views

Can we widen hash functions with concatenation?

There seems to be an interest in wider and wider hash functions. This is understandable as bigger is always better. So there have been questions asking about 1024 and 2048 bit functions. So rather ...
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1answer
624 views

In a Feistel cipher structure, what exactly does the “round function $F$” do?

In a Feistel cipher structure, what exactly does the "round function $F$" do to the right half of the data, before taking XOR of the output with the left half of the data?
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1answer
2k views

How to prove security of a randomized encryption algorithm?

I have designed an random encryption in public key setting. I am convinced about its security guarantee but I need a formal way to prove its robustness. How can I prove the security of this random-...