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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976 views

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
190 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
194 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
272 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
479 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
590 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
706 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
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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
104 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
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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
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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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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
264 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
183 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
141 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
135 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
85 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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342 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
113 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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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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2answers
680 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
302 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
167 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
260 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
156 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
130 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
140 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
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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
255 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
307 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
610 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-...
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1answer
85 views

Does pairings based cryptography inherently require a CRS/trusted setup?

In all algorithms I've seen that rely on pairings-based cryptography (some examples: snarks without PCPs, more snarks, sublinear ring signatures), a common reference string is required. Is this always ...
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2answers
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DRM simple clone

I have been trying to encrypt media(Video and audio content) from a nodejs server to a client like android or iOS. I heard of DRM but could not get a reliable implementation of DRM. I wanted to make ...
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3answers
5k views

Is there a standard, or widely accepted convention, for magic constants in crypto software?

Inspired by Magic "Nothing Up My Sleeve" Numbers - Computerphile - YouTube [5:31]. If you just need a constant to begin your algorithm, and the value of that constant isn't important, why not have a ...
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2answers
556 views

What's the difference between word-oriented and byte-oriented ciphers?

I am currently learning about the RC4 cipher and its improved version called Spritz. The paper of Spritz says We do not consider other stream-cipher proposals here, and expect that for many ...
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1answer
110 views

New Passwording? [closed]

I just want to note before you continue reading--this does not specifically apply to hashes or the key to encrypted messages. However, I am initially thinking about password/key solving/remembering by ...
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2answers
222 views

Secret Sharing Scheme with variable share size?

Is there a secret sharing scheme construction that allows the shares to have different sizes/lengths? For example a (3,3) scheme, where shares 1 and 2 have large sizes while share 3 has a very small ...
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6answers
444 views

Is building your own inefficient but secure cipher hard?

Everyone says you should never build your own cryptosystem. That doing so is hard and the only way you know it's secure is if it stands up to serious scrutiny. And yet, if you are willing to go way ...
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1answer
347 views

Are there any applications of Lie algebras or Lie groups in cryptography? [closed]

I am interested in the applications of algebra in general to cryptography. In particular, I am wondering if there are applications of Lie algebras and Lie groups to cryptography. Are Lie algebras or ...
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1answer
802 views

AES parameters specifications [closed]

I'm writinig manager for all transformations which is described on https://developer.android.com/reference/javax/crypto/Cipher.html There are few questions about how cryptographic algorithm works. ...
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1answer
206 views

Full diffusion or Partial diffusion between s-box applications?

In regards to maximizing active s-boxes: is it advantageous to apply the non-linear layer after complete diffusion of the state, rather after then partial diffusion? Using AES as an example, with ...
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0answers
39 views

DES: Initial permutation position decreases by 8 - what is the significance? [duplicate]

I'm a beginner in the complex world of cryptography. Doing some basic course on DES, and I found a peculiar (to me) pattern within DES' Initial Permutation table. The table is built as an 8x8 matrix ...
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0answers
31 views

Distinct keys but value revealing

Suppose we have a trust party $P_A$ that can be used to manage a data transfer from parties $P_I = P_i, \ldots, P_{i+n}$ which do not trust each others to a party $P_R$ which is also not trusted. ...
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1answer
55 views

Using the same encryption algorithm for different types of content/data

Can text and media content be encrypted using the same encryption algorithm ? and if there's an algorithm that can do that, how does it work ?