Questions tagged [symmetric]

Symmetric cryptosystems assume two communicating entities share a pre-established secret key.

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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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Is lattice-based cryptography relevant in symmetric cryptography?

I've seen that lattice-based cryptography works well with public key cryptography as well as cryptographic hashing algorithms, but does it apply to symmetric key cryptography?
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how are variable key sizes produced?

I am current learning the internal working of several Symmetric key Cryptographic algorithms, and came across DES and AES. DES takes in input a 64 bit key and AES-128 takes in input a 128 bit key ...
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AES encryption question

If we consider the generation of keys as $$\begin{aligned} K_0 &= E_K(IV); \\ K_{i+1} &= E_{K_i}(A) \end{aligned}$$ Where A is a block of zeroes, and the ciphertext blocks are computed as ...
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In GnuPG, what's the difference between --s2k-cipher-algo and --cipher-algo? [duplicate]

I want to change some encryption options while using GnuPG to encrypt a file symmetrically. 1) However, for choosing the cipher algorithm, GnuPG has two commands and I don't know which one to use. ...
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Best practices when encrypting a file with three different ciphers [closed]

I have some files that contain important information, so I want to encrypt them by the most secure encryption method possible. I've read countless StackExchange answers on similar questions and some ...
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Does ChaCha20/Salsa have the same Bit Strength as AES for identical key sizes?

i.e. does ChaCha20 with a 128bit key, require 2^128 attempts to brute force, as with AES-128, theoretically? Ps. notwithstanding that ChaCha is a stream cipher.
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Symmetric property of DDT of inverse function

Given a bijective function $F: \mathbb{F}_2^n \rightarrow \mathbb{F}_2^n$. The entry of the Difference Distribution Table (DDT) at row $\alpha$ and column $\beta$ is defined as $$DDT_{F}(\alpha,\...
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Symmetric Encryption in the P=NP world [duplicate]

I expected to find answers along the lines of quantum-computing insight into attacking AES; however, answers on this question aren't applicable because "Quantum computers give a quadratic speedup on a ...
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Is there a maximum amount of data which can be encrypted using a symmetric (AES256) key?

I am working on an application where we will be encrypting billions of small (< 2,000 bytes) records. Combined, we are facing many TB of data. Each record will be encrypted independently, using a ...
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Are there any symmetric cryptosystems based on computational complexity assumptions?

Are there any symmetric cryptosystems which are provably secure in the sense that there exists a reduction from their security to the hardness of some underlying hard problem such as integer ...
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Key rotation (or other measures) for PASETO v2 “local”

I was looking at using PASETO's v2 "local" encryption (XChaCha20-Poly1305) to implement short-lived tokens to share claims between microservices via an untrusted client. PASETO's documentation is ...
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49 views

Generate $4\times 4$ Sboxes with a given branch number

Say, I want to generate a lot of $4\times4$ Sboxes with linear (or differential) branch numbre of $3$. One idea is to take all the $302$ affine classes, expand each of those classes and check if any ...
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68 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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35 views

Symmetric Key Encryption with the key a seed

Would it be feasible to give two parties a seed to generate random numbers? So that when they want to send data to each other they send the correction on the random number generated? The random ...
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Is it possible to determine the symmetric encryption method used by output size?

I'm attempting to identify the method of encryption for a black-box symmetric encryptor that produces blocks of output that are 4 bytes in length (e.g. small inputs fit in 16 bytes, then 20 bytes and ...
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96 views

How does the key agreement process take place in Virgil E3Kit SDK for end to end encryption?

I'm using Virgil E3Kit SDK to implement end-to-end encryption in my App. Their E3Kit SDK is very effective and not too hard to understand, but I still don't understand how does the key agreement ...
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95 views

Zero-knowledge proof with only a ciphertext

Suppose there is a plaintext p, which is encrypted with a symmetric cipher using a key k, resulting in a ciphertext c. Bob knows both c and k, but Alice knows only c. Is there any protocol by which ...
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What does it mean : “Canonical representative of Sbox is 0123468A5BCF79DE”? and How can we calculate this representative for Sbox?

In paper :Cryptographic Analysis of All 4 × 4-Bit S-Boxes Saarinen has classified $4 \times 4$ S-Boxes and defined Canonical representative for each class of S-Boxes. What does "Canonical ...
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AES: Why is it a good practice to use only the first 16 bytes of a hash for encryption?

I'd like to encrypt Text with AES/CTR and a password defined by the user in java. I already checked the internet (and stackoverflow) for answers. The most used version is to hash the user password ...
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What is the inverse function of the finite field GF($2^3$) and GF($2^4$)?

I am currently reading a paper Cryptanalysis of a Theorem Decomposing the Only Known Solution to the Big APN Problem. In this paper, they mention that they used $I$ which is the inverse of the finite ...
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What does $x^{1/e}$ mean in cryptography in this open butterfly structure?

I am currently reading a research paper that introduces this thing called a butterfly structure. I am confused about the structure of the open butterfly in this paper which has the equation $H^{\...
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Reed Solomon secret sharing and as a one-time symmetric key?

Shamir's Secret Sharing is just a special case of Reed-Solomon where only one coefficient is used to store the secret instead of the entire polynomial. Sarwate however, suggests that the latter can ...
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35 views

Randomly initialised global counter used to encrypt the kth message with IV = IV + k mod 2^n

The use of an increasing IV is not secure for a block cipher. That is, using a random IV for the first message then IV + 1 for the second , IV + 2 for the 3rd etc. How can I construct an attack to ...
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328 views

Is there a symmetric-key algorithm which we can use for creating a signature?

I know that in the asymmetric-key algorithm the RSA signature exists but what about the symmetrical ones?
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How can a node establish pairwise shared key with other nodes using its own polynomial share together with other's public values?

A server has a symmetric bivariate polynomial $ F(x, y) = \sum_{{i,j}=0}^{t-1}a_{i,j}x^iy^j$ $\in GF(p)[X, Y] $ of degree $t-1$. For simpliciy, $ F(x, y) = a_{0,0}+a_{1,0} x+a_{0,1}y+ a_{1,1}xy$ mod ...
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Find encryption algorithm knowing input, output and secret

Today on my PC I found some old backups; they contain also some pictures I encrypted years ago with a smartphone running Windows Mobile but I don't remember the application I used to cipher them. I'm ...
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212 views

CAESAR finalists: Lightweight case (Ascon vs ACORN)

The Ascon cipher has been selected as the first choice in lightweight case and ACORN as the second. However according to Face-off between the CAESAR Lightweight Finalists: ACORN vs. Ascon paper, the ...
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74 views

OAEP security with variable length hash function

I'm implementing a hobby cryptosystem for fun and to increase my knowledge on the subject, and I was wondering if the OAEP construct was still sufficient as an all-or-nothing-transform if variable ...
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2answers
823 views

Insecure private-key encryption

I am learning about crytography and the differences between the public and private keys encryption examples and I was wondering if it is possible to have a private key encryption scheme that is ...
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1answer
76 views

Definition of symmetric cipher and definition of asymmetric cipher

So I'm currently taking a cryptography class right now and my professor has told the class that she can't even define symmetric cipher for us without getting into asymmetric ciphers and the textbook ...
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How does an S-box introduce confusion

I'm trying to find the logic for introducing the S-box, but having trouble understanding why. In a simple cipher, e.g. c = pt xor key I understand that I can ...
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What are dual codes and the codewords denoted by these dual codes in terms of trace?

I am currently reading a research paper (linked below) that mentions "Consider only maps that vanish at 0, their short codes $C_f$ and their duals $C_f^\perp$. The duals can be written as $C_f^\perp = ...
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What is the link between the parity check matrix, double-error-correcting codes and APN permutations?

I am currently reading a research paper (linked below) which mentions that a map $f:V:=GF(2^{m}) \rightarrow V$ which vanishes at 0 is APN if it satisfies the condition that it is a binary code $C_{f}$...
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What does 2-flat mean when discussing APN permutations?

I am currently reading a research paper that uses the term 2-flat. However, I don't understand what this term means. For example, the paper mentions in its definition of APN that for all distinct $a$,...
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Are all block and stream ciphers symmetric?

I'm trying to categorize my knowledge. Can I place block ciphers and stream ciphers under symmetric with RSA/DH under asymmetric?
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Generate one-time-pad with pre-shared key and public randomness

I know very little about cryptography, so I apologize if the question does not make sense. Let's say we design a function $F(P, X) \rightarrow K$ that takes in a pre-shared private key $P$ and a ...
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72 views

How to compare one time pad security and efficiency with AES?

It seems that the minimal size of Pseudorandom permutation (PRP) output is $128$ bits. In general, I'd like to see if there's any minimal size of the output of pseudorandom function (PRF) as well? for ...
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Can POS devices really generate random numbers?

I am doing an implementation of a system designed by a payment company and I am a little skeptical about the way they have designed the end to end cryptography. The system is as follows: There are ...
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2answers
132 views

How many keys in a Hybrid Cryptosystem?

If symmetric cryptosystems have $C^2_n$ keys, and asymmetric systems have $2n$ keys, how many does a hybrid system have? This was in an online quiz from school Company A is considering to adopt ...
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884 views

How Secure is gpg Command Using Symmetric AES-256 From Being Cracked

How secure is any data encrypted using the following command: gpg -o *encrypted_output_file_name* --symmetric --cipher-algo AES256 *file_to_be_encrypted* Can ...
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Computing a probability

Let $(w_1,\cdots,w_l) \in (\{0,1\}^\lambda)^l$, and $r_1,\cdots,r_l $ are chosed as uniformly random from $Z^*_q$ such that $r_1+\cdots+r_l=0$ and $q$ is a large prime number. Also, Let $F$is a ...
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133 views

Explaining Chaotic Cryptography

I will venture myself into studying chaotic cryptography. However, I find it hard to explain what chaotic cryptography entails to those that have some knowledge of cryptography. Neither can I explain ...
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121 views

Format of hybrid crypto envelope structure?

From posts including the accepted answer to How to encrypt file with RSA and AES that anyone with RSA key can decrypt them? hybrid crypto (AKA envelope encryption) a GPG-encrypted file has an ...
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1answer
51 views

Send content to owner of gpg public key, nested content symmetric encryption

If I want to encrypt a text content file using a symmetric algorithm like AES, is there a standard format gpg will expect, where it can detect a symmetric key (encrypted with recipient gpg public key ...
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PRGs exist if computationally secret encryption schemes exist

I have understood the "equivalences" between PRP, PRF and PRG. Now, I just read an statement in my lecture notes that made me think that there has to be a conversion between PRG and computationally ...
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One-time pad question (Old ciphers) [closed]

The plaintext SECRETIVE is encrypted using One Time Pad with key DDDDDDDDD. Which of the following is TRUE? The ciphertext will be the same as using Caesar cipher with key of 4 The ciphertext is the ...
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333 views

Security of AES after key expansion 4-MB with ECB and CBC

My question is, how does the security depend or change if I encrypt with AES-128 in total 4-MB of Data? With Electronic Code Book Mode and Cipher Block Chaining Mode ? Does an adversary still ...
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1answer
113 views

Detect MITM with hashed session-key — Is my protocol secure?

I have the following setup: An app ("client") wants to communicate securely with a device I created ("server"). The client has the public key of the server (and a hashed password) preinstalled. I use ...
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76 views

Can a message be encrypted with BOTH mono-alpha and poly-alpha ciphers?

For my class assignment, I was given this text; Qpuvu vo vv stazpuykzh Hhycmlmv asb. Ad dhyaqva wh uyo uzb jpwww Avlw. Tkpjllfdmbp zoatz vzjavfvna ZLHqh. Amva luy yyvlz yu bhk zua zlhvvalaz yow ...