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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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Generating a MAC on a Polynomial

In the following, all the operations and polynomials are defined over a finite field of prime order, $\mathbb{F}_p$, where $p$ is a sufficiently large prime number. All polynomials and values below ...
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Algorithm/encryption technique which outputs a set number of numerical digits e.g. 20 digits from a given input

What the name of the algorithm/encryption technique which outputs a set number of numerical digits e.g. 20 digits based on some input. You can input some data e.g. text or numbers but the output is ...
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What is the most secure encryption algorithm that keeps the entropy the same or even lowers it? [on hold]

On top of my mind comes caesar cipher, but that is not really secure so what is the most secure encryption algorithm that doesn't affect entropy or even lowers it? I know this might not be as ...
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1answer
47 views

Is there an algorithm that allows to distribute elements securely between parties?

Let's say we have a set of numbers $n = \{ 1, 2, 3, 4, 5, \ldots \}$ and $m$ players ($m < \operatorname{sizeof}(n)$, of course). I want to know if there's a way for all $m$'s to pick different ...
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2answers
80 views

Is obfuscation considered a cryptographic primitive?

The general definition of obfuscation is the process of obscuring a message (not necessarily source code). There is a "rigorous" method for obfuscation (indistinguishability obfuscation, ...
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Is there a name for encryption which relies on repetitive calculation (=time) instead of a key-value? (e.g. block chain, hash value, block cipher)

Many encryption problems are fast to solve if a key, factor, exponent or something similar is known. Other encryption methods don't have such keys. E.g. a hash value of another value. It's used ...
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30 views

GCD in Montgomery arithmetic

Wikipedia article on Montgomery modular multiplication contains the following statement: Many operations of interest modulo $N$ can be expressed equally well in Montgomery form. Addition, ...
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In search of a pedagogically simple example of asymmetric encryption routine?

(I am not a cryptography expert; I do write software) I am working with some youth (ages 11-13) and wanted to explore for an hour or so some basic cryptography. Doing symmetric ciphers is pretty ...
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Why is ECB+CTR not a thing?

AES-CTR is nice for its parallelizability and simplicity but if you duplicate an IV you reveal plaintext. Chaining modes like CFB and CBC don't have that problem per se but they are not ...
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Is there a 'chain-function' which allows computing the value for the index which is next, previous, +/- some constants but has no shortcut for other?

Looking for an algorithm which has a cyclic 'chain'-function which only allows the computation of next, previous element and in addition to that also a shift by a small amount of constants. Example 1 ...
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Does a digital signature algorithm exist which has a normal, a blind, an elliptic curve and an elliptic curve blind version?

Q: Does a digital signature algorithm exist which has a normal, a blind, an elliptic curve and an elliptic curve blind version? I am searching for an algorithm where you can see what happens if you ...
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50 views

Is there a way to easily encode a message without a computer on either end?

I enjoy making notes and passing them to my friends, and I also like making them encrypted for no reason. My friends enjoy it too, but it's a bit annoying to use the Caesar cipher for everything ...
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Do any block cipher encryption functions (or similar functions) exist which are associative to each other and cyclic?

Most block ciphers encrypt a plaintext deterministically into a ciphertext which allows decryption in the opposite direction. Now, instead of encrypting just one plaintext, I'm looking for a cyclic '...
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57 views

Do there exist cryptographic algorithms where the “core” function is 96-to-32-bit?

There exists a FOX family of block ciphers (Wikipedia article: IDEA NXT). This cipher uses a function called "f32" which operates on three 32-bit words and outputs one 32-bit word. This function ...
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1answer
155 views

Why doesn't GMAC/GCM encrypt its authentication tag?

As most know, a duplicate nonce with GMAC/GCM allows key recovery attacks against GMAC itself and thus the ability to forge messages. This is because GMAC computes GHASH and then just XORs this with ...
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1answer
74 views

Are there any LFSR-based ciphers with variable feedback polynomials?

All LFSR-based stream ciphers that I know of use a fixed feedback polynomial (i.e. the taps are always in the same position). I know that, at least for non-trivial output lengths, it is necessary to ...
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Can zero-knowledge proof be used to determine if another person knows a certain movie with a twist ending?

Suppose I want to talk with a co-worker about a movie called "The Twist Movie". I know the movie contains an interesting twist, and bringing up the movie in a discussion about twists in movies might ...
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134 views

Efficient way of generating a random number of N (less than 64) bits with exactly M bits equal to one [closed]

Would there be an efficient way to implement a function with the following signature: unsigned long long int random_word(size_t n, size_t m) that would generate ...
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3answers
337 views

Nonce-misuse-resistance scheme applied after the fact to AES-GCM for defense in depth?

This is a follow-up to a previous question about encrypting IV/MAC results from AEAD ciphers. I have a system I'm working on that needs to use standard (NIST/FIPS) cryptography, at least for its ...
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Are there any cryptographic methods which use multiple cyclic groups?

For some cryptographic methods you can construct them. e.g. elliptic curves (product of two cyclic groups) or Diffie–Hellman (can be product of n-cyclic groups). But they have no usage because at a ...
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1answer
76 views

Risks of publishing multiple signatures

Is there a risk when publishing multiple signatures for the same message? For instance, an ECDSA key (using an EC key) and a RSA-PSS signature (using a RSA key). The context of my question is the use ...
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1answer
109 views

Is Permutation conjugate problem hard?

Let $x$,$y$,$z$ be permutations. Then public key is $z=xyx^{−1}$ and $y$. Is permutation conjugate search problem easy? if yes, how to find $x$ from $z$ and $y$? Let be a is Alice's secret key as ...
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How to encrypt a small number of identities (which are related to each other)? / Which algorithm has the smallest bit-length?

I'm looking for an encryption with as small numbers as possible. Given a small group of identities ($G$) (e.g. numbers from $1$ to $N$). Given one entry (or a small number) $e_i$ allows to compute ...
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1answer
212 views

Are “non-mathematical” encryption algorithms comparably secure against brute force key recovery?

I recently learned about a desktop encryption application called ALKEMI, which does not use mathematical encryption according to the website, which I understand to be a misnomer, at best: The ...
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1answer
140 views

How to construct a “toy” version of Gimli permutation for three (instead of twelve) 32-bit words?

I am interested to see a "toy" version of the Gimli permutation for three (instead of twelve) 32-bit words. I see that the "core" sub-permutation of Gimli operates on three 32-bit words, but I don't ...
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18 views

Off-Chain Channel With Multi Participants That Have Different View/Write Access

I'm looking to expand my blockchain ability to have off-chain channels between different participants (let's say more than 2 participants). The requirements: Only the participants of the channel ...
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Constructing Low-Density Parity-Check Codes of length $n$ and minimum distance = $\delta n$ over $GF(q)$? [closed]

I am looking for a way to construct an LDPC (Low-Density Parity-Check) Code $C$ of length $n$ and minimum distance $d_C$ that scales linearly to $n$, meaning $d_C = \delta n$ for $\delta \in (0,1)$. ...
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Determining which encryption algorithm to use [closed]

I'm a traditional software engineer. Recently, due to the nature of a current project, I have been exposed to many cryptographic libraries--there are so many encryption algorithms! How do you choose ...
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1answer
83 views

Reversible Decryption in Symmetric Key Algorithms

I am currently learning the Internal Working of Symmetric Key Algorithms, like DES, AES, BlowFish, IDEA just to name a few. These are all quite complex Encryption alogrithms, which requires a lot of ...
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1answer
40 views

Does any problem arise when the order of an elliptic curve is equal to its prime field modulus? [duplicate]

Regarding cryptographic schemes in elliptic curve cryptography, is there a problem with having the order of an elliptic curve being equal to its prime field modulus? That is, an elliptic curve where $...
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52 views

Modifying Elliptic Curve Parameters

For context, I was watching this bit of the video: which goes over this source code. The piece is about elliptic curve cryptography and how it works. I want to use some of this knowledge to make my ...
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1answer
115 views

Why does a padding block exist for ECB and CBC modes?

In ECB and CBC mode, the size of cipher text is more than the plain-text size by one padding block. From what I read, ECB does a simple encryption to each 64 bit block of a Plain text, and produces ...
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48 views

Chinese remainder theorem

Z/11Z[X] is the finite field P(2) = 4 P(3) = 3 P(5) = 7 How can I solve my congruence system with polynoms? I made my system of congruence like that : X = 2 [4] X = 3 [3] X = 5 [7] And it gives me ...
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1answer
81 views

Cryptography on programming

In pursuit of understanding a randomly found topic I was interested in learning the connection between integer programming and cryptography and found Lenstra Jr.'s Integer Programming and Cryptography....
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2answers
108 views

Why is prime number size important for RSA security?

RSA modulus is $N = pq$ where $p$ and $q$ are prime numbers. I read from somewhere that the time it takes to decrypt the RSA encryption increases exponentially as key length increases, which depends ...
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Aside from Keccak, are there any keyed/unkeyed permutations where the choice of all rotation constants is not based on heuristic methods?

I am interested to see examples of cryptographic algorithms (namely, keyed or unkeyed permutations that transform an $n$-bit input to an $n$-bit output) where the choice of all rotation values is not ...
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1answer
88 views

Bit-strength of discrete logarithm for a group of integers modulo a safe prime

Preliminaries Let $p$ be a safe prime number. Let $\mathbb{Z}_p^*$ be the multiplicative group of integers modulo $p$. We have $\mathbb{Z}_p = \{\,a \in \mathbb{Z} \mid 1 \le a \lt p\,\}$ . Let $g \...
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3answers
202 views

How can a hash have a fixed length?

I am very new to cryptography, I apologize if my question is so basic. I do not understand how a hash can have a fixed length, because you can have infinite inputs to a hash function. With a fixed ...
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1answer
71 views

How to symmetrically encrypt 64bit values?

I'm curious about an algorithm that would be good for the following scenario: 32-bit "plaintext" input, taken from a counter 32 or 64-bit "ciphertext" output It should be possible to decrypt the ...
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2answers
143 views

Choosing the size of an S-box

The most common S-boxes that I've seen are 4-bit and 8-bit (I've seen a 3-bit S-box in PRINTcipher, but I'm pretty sure they only did so due to significant hardware constraints). I understand that ...
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1answer
33 views

Which is the fastest way to find a member of a subgroup with known size modulo prime $P$, with know factorization of $P-1$?->$x$ with $x^s \mod P = 1$

Assuming you know the factorization of used prime $P-1$ $P-1 = s \cdot f_2\cdot f_3...f_i$ Now you want to find a member of a subgroup $\mathbb{Z}_s$. This means any $x$ with $x^s \equiv 1 \mod P $ ...
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1answer
126 views

New Cryptographic Algorithm [closed]

I was wondering about an algorithm that would take a bitstring as an input, shuffle it and output it. You could use a deterministic RNG to select pairs of bits to swap, using the seed as some sort of ...
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24 views

Security implications of an extra inner encrypt for a single block Matyas-Meyer-Oseas hash function

Was giving some thought to simple MMO constructions for fast single block hash functions for things like PQ crypto. There's Haraka, but that's not standard and readily available while simple AES is in ...
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51 views

Unique numbers with $P^aQ^bR^c \mod N$ for each combination of $a,b,c$ possible? Would it be safer than separate form (like $T^a \mod P$ for each)?

Main question: Is the computation of $a,b,c$ in $P^aQ^bR^c \mod N$ (much) harder than in $T_p^a \mod P$, $T_q^b \mod Q$, $T_r^c \mod R$ ? (assuming the first form exists) $P^aQ^bR^c \mod N$ With $P^...
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1answer
43 views

How much more secure is $c = mg_1^r + g_2(g_1(g_1^r-1)/(g_1-1)) \mod p$ compared to just $c = mg_1^r \mod p$ (dis. log), all known but $r$?

To encode a message $m$ to a cipher $c$ you can use the only hard solvable problem of computing the discrete logarithm with a generator $g$ in base over a prime $p$. $c = mg_1^r$ mod p If an ...
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2answers
110 views

Origin of values for “security margin”?

It seems that the acceptable "security margin" for ciphers is set to be between 25% and 30% as a target by designers, where this number represents the number of rounds that remain "unbroken" for a ...
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1answer
152 views

Deterministic Authenticated Encryption with AES-OFB and HMAC

I have an encrypted column in a database that stores sensitive information. The existing encryption scheme is deterministic and a database index exists on the encrypted value to allow searching. I am ...
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2answers
73 views

human readable unpredictable & no collision uid based on time

I need to create an unpredictable uid based on time. I plan to allow it to work during a time frame of 100,000,000 seconds. So the seconds will go from 00000000 to 99999999. I need an algorithm that ...
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1answer
84 views

Comparing Shanks' Algorithm to Brute Force

I'm trying to understand how/why Shanks' algorithm solves the discrete log problem $y=g^x \bmod p$ faster than a brute force search does. Any explanation would be great.
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49 views

How to create an ultra-secure connection between two clients with xor? [closed]

At work, I was asked to create ultra-secure connection over lan between two computers. It will be some kind of messager. I have a bunch of same random data in them(near 100mb). Also I can start a ...