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Questions tagged [cryptography]

Questions about the construction and analysis of protocols and algorithms for secure computation and communication (including authentication, integrity, and privacy aspects).

Cryptography studies techniques for secure computation and communication, i.e. secure storage and manipulation of information, both theoretical and practical.

The purposes of cryptography include confidentiality (leading to ), data integrity (leading to functions), authentication and more. Cryptography often relies on algorithms based on mathematical operations to transform data. Cryptography also includes the study of secure communication protocols.

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Can a public key be used to decrypt a message encrypted by the corresponding private key?

From what I have seen about usage of a pair of public and private keys, the public key is used for encrypting a message, and the private key is used for decrypting the encrypted message. If a message is encrypted by the private key, can it be…
Tim
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Meaning of: "'If factoring large integers is hard, then breaking RSA is hard,' is unproven"

I was reading CLRS and is said: If factoring large integers is easy, then breaking the RSA cryptosystem is easy. Which makes sense to me because with the knowledge of $p$ and $q$, it is easy to create the secret key which the knowledge of the…
Charlie Parker
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What is an extremely basic asymmetric cipher that I can present at the pub?

I'm trying to explain the basics of Bitcoin to my parents. One of the core components of bitcoin, is signing transactions to make sure your identity can't be impersonated, and thus the need to explain a simplified asymmetric cipher. What's an…
Ryan Leach
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Given RSA, why do we not know if public-key cryptography is possible?

I was on wikipedia on list of unsolved computer science problems and found this: Is public-key cryptography possible? I thought RSA encryption was a form of public-key cryptography? Why is this a problem?
Namster
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Why is fully homomorphic encryption so slow?

What are the reasons that FHE is so slow? Is it possible to make the FHE algorithm so fast that it can be used in practice (say, the practical FHE algorithm should be slower no more than 10 times compared to conventional calculations)? Or there is…
user92507
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Blockchain cipher suitable for preschoolers

Is there a cipher that well suited for preschool-aged children to work out on pencil and paper, to learn concepts of block chains? It must have the following requirements: Able to be easily verified a. For example, Joe submitted red, but Suzy…
Aaron Thomas
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Encrypting a 180-bit plaintext into a 180 bit ciphertext with a 128-bit block cipher

I have a field in my data store which must take exactly 180 bits of information. Some users will choose to make this data encrypted, some won't, so some of those 180 bit fields will be ciphertext some will be plaintext. A boolean will indicate which…
jjdjdjdj sjsjsjsjs
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Partially homomorphic encryption (on addition modulo N) not based on prime factorization

A cryptographic function is homomorphic on some operation if that operation is preserved in the encrypted data. Such a function is homomorphic on addition modulo if the following holds for some cryptographic function $E$: $ E(x)\cdot E(y) =…
user13675
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What is a protocol for determining which of two numbers is larger, without sharing those numbers?

Situation: Alice has selected a positive integer $a$, and Bob has selected a positive integer $b$. Alice and Bob want to know whether $a > b$, $a = b$, or $a < b$, but neither wishes to reveal their chosen number to the other party. How can Alice…
senshin
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Trustless exchange without a third party

Is there a cryptographic (or even not entirely cryptographic) way of exchanging objects between Alice and Bob that would not require a third party, and Alice and Bob would not need to trust each other? For example, Alice and Bob have Y and X objects…
Lee J.
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Proof of correctness of the XL-algorithm for polynomial systems

Section 12.4 of G.V. Bard's Algebraic Cryptanalysis discusses the XL-algorithm (first reported by N.T. Courtois and A. Shamir in Efficient algorithms for solving overdefined systems of multivariate polynomial equations and Courtois' thesis). The…
user13675
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Perfectly Secure Ciphers known other than the OTP

By Information-Theoretic definitions, the One Time Pad (OTP) is called/was proved to be a Perfectly Secure Cipher. For the sake of completeness, we define OTP: An enc/dec function, $f:\mathcal{P} \times \mathcal{K} \rightarrow \mathcal{C}$ Perfect…
Subhayan
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Is F(F(s,x), x) necessarily a PRF if F is?

Given a PRF - F, is $G_s(x)=F_{F_s(x)}(x)$ necessarily a PRF? First I thought how to tackle this problem. First I tried using a hybrid argument: $|\mathbb P[F_{F_s(x)}(x)] -\mathbb P[f(x)]|\leq |\mathbb P[F_{F_s(x)}(x)] -\mathbb P[F_{f(x)}(x)]| +…
Yuval Kirstain
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Proof of non-receipt of the file

The condition of the problem and the statement of the problem: Alice pays Bob for the fact that he, at the request of users, gives out files of interest to users. For example, the user is interested in the file #hash1. The user learns from Alice…
J. K.
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dining metaphysicians problem

Here is a problem vaguely related to the dining philosophers problem. Three metaphysicians go to a restaurant for dinner. When it is time to pay the bill, they decide that they want one of them to pay the entire bill, but without the other two…
maibaita
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