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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Encryption algorithm with random number generator and seed

I am an amateur working in another field, but I am interested in CS. Recently, I dabbled in cryptography. I came up with the following to encrypt text: 1: convert text to unicode bit representation ...
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How Secure Is This One-Way Function (Key Schedule)

While thinking about cryptography and how to "derive a key schedule" (like in AES), I thought of an algorithm that I can't figure out how to reverse (which is good). It's very simple and ...
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Is there an efficient algorithm that allows to construct a cryptographically secure $n$-bit hash function based on two unkeyed $n$-bit permutations?

Let $f(x)$ and $g(x)$ denote two independent, “ideal”, unkeyed, public $n$-bit permutations (two publicly known bijective functions that produce $n$-bit outputs from $n$-bit inputs), where $n$ is an ...
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Cryptography scheme to prove you really are the author for something

Say I'm a researcher like Satoshi Nakamoto that wants to stay anonymous. I want to publish documents and sign them somehow. A few years, I want to reveal my identity and prove it was me who was ...
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1answer
621 views

Padding Oracle Attack with AES-128-CTR and MAC

Assume Alice and Bob are communicating using 'MAC then Encrypt' paradigm. Specifically, they are using HMAC with SHA256 as the hash function and the output is truncated to 40 bits. They are using AES-...
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1answer
355 views

What does “$<\!\!<\!\!<$” mean?

What does the symbol $<\!\!<\!\!<$ mean? It is normally followed by a number. An example: It would be appreciated if you could explain it in fairly basic terms.
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1answer
25k 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 ...
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1answer
53 views

Can the EdDSA signature scheme be customized with OpenSSL?

EdDSA has currently 2 signature scheme Ed25519 and Ed448 where Ed25519 is the EdDSA signature scheme using SHA-512 (SHA-2) and Curve25519 Ed448 is the EdDSA signature scheme using SHAKE256 (SHA-3) ...
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70 views

Anamorphic Cryptography, what do you think about it? [closed]

I'm currently working on a personal project using a special kind of crypto I've imagined (noooo please don't !!!), called the Anamorphic Cryptography. The project: create a complete keyless ...
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1answer
53 views

What papers describe the rationale behind cryptography algorithms

I am trying to introduce myself to cryptographic hashing and encryption. I am looking for original papers of sorts, to describe the inspiration behind why they choose certain numbers, if they are ...
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1answer
105 views

Montgomery Multiplication with CRT

I am attempting to understand how to use Montgomery multiplication in an RSA private key operation: $X \equiv a^{e} \pmod{n}$ where $a$ is the message, $e$ is the exponent, $n$ is the modulus. Using ...
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2answers
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What's the name of this random number generation algorithm?

I'm looking for the name of an RNG method or algorithm, described below. Combining multiple results of a non-uniform random number generator can produce a more uniform result. It seems like this would ...
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4answers
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Is there a string that's hash is equal to itself?

I was wondering if there's any string that has a hash equal to itself, so that – when using any (none specific) hash function – the hash would be equal to that string? so that: ...
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1answer
118 views

Error correcting codes that are indistinguishable from random

Suppose you have a public program P(n) which takes message n and generates an encrypted output (utilizing asymmetric cryptography) for some entity which has the private key to decrypt it. Using a ...
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47 views

How to design number of rounds in my cipher?

I have specific cipher which is built from permutations. It has or should has few rounds. If we do 2 rounds it is like 2 permutation composition. 3 rounds are like composition of 3 permutations and so ...
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1answer
101 views

Cryptographic function that can 'pack' numbers

Is there a cryptographic algorithm that can 'pack' a bunch of strings/numbers and "confirm" if a string/numbers exists (later in the code) while keeping the output hidden? For example, I have ...
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How to construct a “toy” version of the Ascon permutation?

I want to obtain a “toy” version of the Ascon permutation defined for five 8-bit words (instead of five 64-bit words.) It seems that it is possible to use the same bit-sliced 5-bit S-Box. But is it ...
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Are there popular and secure Authenticated Encryption schemes with Salsa20/Sosemanuk in CTR-mode with a Carter-Wegman MAC?

I read that AES/GCM is a good choice for authenticated encryption because: AES has very strong heuristic security Encrypt-then-MAC leaks no information about the plaintext The CW-MAC in GCM can be ...
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2answers
943 views

If the first key-bit is flipped, which DES s-boxes are affected?

Instead of the input bit being flipped... if the 1st bit of the key is being flipped, which s-boxes are affected during encryption/decryption of DES?
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Help on validation code algorithm [closed]

I wonder if someone can help me find the algorithm used to generate validation codes from a serial number. I already have some working examples of serials->codes pairs: 19003148 -> 523254 19003162 -...
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27 views

How to determine the maximum number of times the DES algorithm needs to be run?

I am only a beginner in cryptography and I am getting confused by the following: Question Consider a known-plaintext attack performed on a double-DES cryptosystem. (a) Determine the maximum number ...
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35 views

Approach used with XOR cipher in black box scenery

What's the approach used in cryptanalysis to make an decrypter for a simple xor stream cipher in a Black Box scenery with only the output?
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1answer
50 views

Multiparty dataset intersection count

Typically, Private Set Intersection (PSI) protocols let you learn the subset of items on each party's dataset that are in the intersection. The problem in this case is a relaxation of these kind of ...
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1answer
60 views

How to calculate RSA Key Size correctly starting from 384 bits to 15360 bits or beyond 15360 bits

Hello fellow experts here, I am new to cryptography. Recently I looked into RSA Key Size (Microsoft RSA library), it actually describes that the minimal key length required is 384 bits and maximum ...
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34 views

How to calculate degree of confusion of an encryption algorithm?

I am programming an encryption-decryption model in python 3. I want to check its strength. I found 3 methods to check, they are: 1. Degree of diffusion 2. Degree of confusion 3. Integrity check For ...
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745 views

One ciphertext, multiple keys, multiple messages

I recently came across following idea, does anyone know a name and if it is actually used? A wants to send B a message (A and B know both have a common secret key) and C wants to intercept it (...
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1answer
30 views

Can MFA codes be predicted if you know what their values were at a previous time?

I use an app on my phone that, after scanning a QR code on a website, gives me 6-digit codes which change every 30 seconds. These codes can be used for Multi-Factor Authentication (MFA) on some ...
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1answer
58 views

easy hash algorithm to use without computer [duplicate]

I am searching for a simple hash algorithm(s) which can be used to calculate relatively secure hash without using of any computer. Some requirements: use only simple arithmetics operations (+ - / *, ...
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Crypto-Compression Algorithms?

I was wondering, whether there exist such algorithms/enciphering procedures which both compress and encrypt the input data. That means, for starters, the output will be both smaller in size and ...
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Finding the relationship between generating elements represented by a Hamiltonian cycle of a Cayley graph (like in strong RSA condition)

Consider an undirected Cayley graph of a finite group $\mathbb{Z}_p \times \mathbb{Z}_q$, where $p$ and $q$ are distinct primes. Let the generating set for the Cayley graph be $S=\{g_p, g_q\}$, where $...
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How could I verify that a contract was actually sent to me from the client as soon as the contract is received?

with the information provided - what would be the best solution - something like document management program like IBM Filenet ? or trusted timestamping? If I want to store electronic contracts for ...
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How to disperse personal data before returning?

I am working on a project that is dealing with personal data. The task is to find a method such that when user makes a query into multiple institutions, the result will contain already scattered/...
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34 views

WPA/WPA password algorithm

I would like to understand the mechanism behind wpa/wpa2 algorithm. Is there any script that can put this theory:(Key = PBKDF2(HMAC−SHA1, passphrase, ssid, 4096, 256)) into action to test it ? I made ...
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57 views

What are the standard properties of an S-Box [duplicate]

Apart form the following, what are the other properties of a good cryptographic Substitution box or the S-Box: Changing one input bit should change about half of the output bits. Each output bit ...
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1answer
67 views

Is there a term for cryptographic attacks where you can verify decryption without assuming any known structure on the plaintext?

The questions https://security.stackexchange.com/questions/1696/if-someone-breaks-encryption-how-do-they-know-theyre-successful and https://security.stackexchange.com/questions/119887/how-to-know-if-a-...
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2answers
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Concerns about use of MAC in my specification

Here is the pseudocode for a routine I am designing: ...
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How does one ensure that a handshake protocol is secure assuming all underlying cryptography used are secure

Suppose one have to design handshake protocol using known secure cryptographic algorithm. The designer of implementer can assume that crypotography is secure but how would they ensure protocol itself ...
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1answer
34 views

With the random numbers generated, can I know which RNG seed was used?

My teacher challenged us to find out which seed was used to generate some random numbers. I would like to know if it is possible to decipher the seed using the generated numbers (break the linear ...
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1answer
63 views

Are there any algorithms for which generating any zero-knowledge proofs is not practical?

It is related to my earlier question: Can zkSNARK or other zero-knowledge proofs be used to proof message authenticity without revealing private key? Are there any algorithms for which generating ...
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1answer
78 views

Can zkSNARK or other zero-knowledge proofs be used to proof message authenticity without revealing private key?

The situation: Alice and Bob are exchanging messages encrypted by some known asymmetric encryption protocol. All their encrypted messages, as well as public keys are intercepted by Charlie. Can ...
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1answer
43 views

How can I get VMAC Code in pure c?

I had find a paper about VMAC algorithm:VMAC: Message Authentication Code using Universal Hashing. Now I want to implement this algorithm, But i don't find test vectors about it. Who can give some ...
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1answer
61 views

How modern messengers encryption keys can't be hacked [closed]

I dont know is this question more like reverse-engineering or cryptographic. Why governments are hunting for encryptions keys? Aren't they delievering by the network the same as the encypted messages? ...
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3answers
541 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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1answer
332 views

I'm trying to understand which cryptographic algorithm is this

I'm reversing a cryptographic algorithm. This is part of the encryption function translated to python (starting from assembly code): ...
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66 views

What is meant by the duality and homomorphism of an encryption algorithm?

I am new to the field of cryptography and security so spare me with this question. What is the general idea of duality and homomorphism of an encryption algorithm? And how one may prove those two ...
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1answer
66 views

How to generate a 16 X 8 perfectly nonlinear S-box

I want to generate a 16,8 perfectly nonlinear S-box for an encryption algorithm I am working on. I don't have a background in math, and I'm an undergrad, so a lot of the math involved is very ...
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1answer
61 views

Are PQ/Classical Hybrid Key Exchanges a reflection of how little we trust PQ cryptography primitives?

My students have asked me some questions about why there are standards being developed for hybrid public key systems with both a classical and a post-quantum component. Given that when elliptic ...
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3answers
477 views

Is it possible to exactly reverse engineer an unknown cipher inside a black box?

Consider the following arrangement:- There is an unknown cipher algorithm operating inside the black box. You can enter infinite key /plain text pairs, and observe all of the outputs. The box might ...
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1answer
96 views

Is it possible that a signing algorithm produces no output?

I am reading Vadim Lyubashevsky's paper on Lattice Signatures without Trapdoors and I came across a somehow counter-intuitive part where he defined an algorithm $\mathcal{A}$: $y\leftarrow D_\sigma^m$...
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1answer
114 views

Non-repudiation and digital signature of a dishonest participant

Let's assume a dishonest Alice who sends, encrypts & digitally signs a message to Bob. Bob stores the decrypted message and the digital signature in a database. However, Alice is a bad girl and ...

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