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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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38 views

### Should I proceed with this for my project? Is it correct?

We have: Select five Prime numbers $p$, $q$, $r$, $s$ and $t$ Compute $n=p*q*r*s*t$ Calculate $Φ(n)=(p-1)(q-1)(r-1)(s-1)(t-1)$ Collect $e$ such that $p < e < Φ(n) … Φ(n)$ and $n$ are co-prime ...
41 views

### Why does solving the underlying polynomial system “break” the multivariate cryptosystem

I was wondering why exactly does solving a polynomial system (directly or indirectly) "break" a multivariate cryptosystem as a digital signature. I realize that the exact reason differs from system ...
92 views

### How does this formula work $(aG + bG) = (a + b) G$ in ECDSA?

Please explain how does this formula $(aG + bG) = (a + b) G$ work in ECDSA? According to the source: $a$ and $b$ are different private keys Suppose $a = 3$ $b = 4$ then the public key is $Q = aG$...
74 views

### When Frankensteining ciphers together, why does order matter? [duplicate]

In a comment on this answer, Cort Ammon states I have heard interesting solutions to these issues involving encrypting something with a proper tested algorithm first (not second), and then ...
8k views

### Creating cryptographic algorithms at runtime

Would it be possible to create a program with which to create a cryptographic algorithm (i.e. encryption or hash) using well-known elements of other algorithms in the same way that algorithms "reuse" ...
11 views

### OpenSSL performance test on a specific file [migrated]

I m new in this world of Cryptography. I`m trying to check the performance of the various algorithms on with OpenSSL. Looking on the internet I find this command : openssl speed aes-128-cbc des ...
34 views

### Is it possible to decrypt a message if a hash of the message was used as a key to encryption [duplicate]

I encountered a scheme where a hash of a message was used to encrypt the same message: result = Encrypt(message=m, key=hash(m)) Specifically: ...
60 views

### Is there such a thing as shortcutable key stretching?

I'm curious if there's a cryptographic (or mathematical) technique for key stretching that allows someone with a secret to quickly derive the final key, requires a deterministic number of rounds for ...
70 views

### 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 ...
51 views

### 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 ...
63 views

### What is the most secure encryption algorithm that keeps the entropy the same or even lowers it? [closed]

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 ...
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 ...
83 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, ...
43 views

### 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 ...
32 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, ...
415 views

### 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 ...
1k views

### 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 ...
23 views

### 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 ...
23 views

### 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 ...
58 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 ...
38 views

### 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 '...
60 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 ...
166 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 ...
78 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 ...
71 views

### 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 ...
137 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 ...
360 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 ...
117 views

### 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 ...
79 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 ...
114 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 ...
35 views

### 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 ...
222 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 ...
146 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 ...
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 ...
45 views

### 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 $\delta \in (0,1)$. ...
72 views

### 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 ...
90 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 ...
41 views

247 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 ...
73 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 ...
185 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 ...
### 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 $x^s \equiv 1 \mod P$ ...