Questions tagged [symmetric]

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

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Clarification needed on encryption concepts [closed]

Symmetric Encryption Algorithm AES provides: Confidentiality (Yes and it is very obvious) Authenticity (I think yes but some blogs say no, assuming only the parties communicating, have the shared key ...
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Why do web-services tend to use preshared secret keys for client authentication instead of public keys?

Every API that I have ever signed up with gives you a secret key that you can then paste into your application. They know the key, and so do you. (The one exception may be VAPID for Web Push). Why is ...
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Do symmetric and skew symmetric key schedules have any known weaknesses?

A symmetric key schedule is a key schedule of the form $(k_1,\dots,k_{n-1},k_n,k_{n-1},\dots,k_1)$ or of the form $(k_1,\dots,k_{n-1},k_n,k_n,k_{n-1},\dots,k_1)$. A skew symmetric key schedule is a ...
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How LastPass decrypts database on web browser?

According to video from Dr. Pound, password managers (LastPass in particular) holds encrypted image of your data on their servers and then with master password you authenticate to get encrypted image ...
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How to destroy a randomly generated key after using it?

for example, I have an encryption program like this: Input: a message, M; my public key Kpub Step 1: randomly generate a ...
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AES vs Kuznechik (GOST R 34.12-2015) comparsion [closed]

Which algorithm is more crypto-resistant: AES or Kuznechik (GOST R 34.12-2015)?
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Encrypting a document with 2 different keys

Is there a way to encrypt a file with 2 (or more) keys and then access it with only 1? Scenario: Bob and Alice have a tight memory and can only remember ONE key. Bob and Alice encrypt a file with ...
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Can raw hash be used as secret key

I am trying to use argon2 hash to derive secret key to be used for AES-GCM , in package argon2-cffi in python there is a function argon2.low_level.hash_secret_raw(secret: bytes, salt: bytes, time_cost:...
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Can cryptographically secure randomness be used to implement one time pad?

if I use an one time pad key generated using a cryptographically secure random source like python's secret module , to encrypt a message, will the one time pad scheme be secure? I think the entire ...
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What happens if the number of message queries are restricted?

In this thread, we only consider symmetric key encryption. I am not familiar with this field, so I am somewhat of an idiot myself. The usual symmetric key encryption allows unbounded queries of ...
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is HMAC required if i am using AES-CFB and using Digital signatures for Authentication

I researched online and found AES-GCM and ChaCha20Poly1305 aren't post quantum secure. So I am planning to use symmetric AES256 cipher in CFB mode do I need to implement MAC using HMAC like HMAC-...
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Use blake2 permutation as a block cipher

Blake2(1024 bit state) permutation (compression function core) is basically a modified ChaCha permutation. One of the modifications is to mix in message bits (key schedule?). Given that blake2 is a ...
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Is a static IV really less secure than an IV generated from a master key?

As an example, let's take a simple situation where AES-256-CBC with IV + MAC is used to encrypt a given plainText and offer authentication. ...
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When would we need a bigger IV than 2 bytes when the IV is derived of a master key?

As an example, let's take a simple situation where AES-256-CBC with IV + MAC is used to encrypt a given plainText to offer both authentication and prevent identical cipherTexts. ...
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Whats a practical and safe encryption to use today? [duplicate]

I'm new to making applications that encrypt sensitive data and so don't know where to start. My question is what is a good encryption scheme that can be run in a good time for normal application and ...
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Distinguishing key reuse in encryption algorithms

Let $E$ be any encryption algorithm, and consider the following game capturing key reuse. Alice samples a key $k$ Bob sends a set of messages $\{m_1, ...,m_n\}$ to Alice Alice flips a coin if heads ...
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Sponge Duplex authenticated encryption with nonce reuse or no nonce

With a Sponge permutation in a Duplex construction for authenticated encryption. illustration example: ascon; actual interest if relevant: keccak Suppose there is no associated data and there is no ...
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Encrypting two messages with the same content with different keys/IVs still secure if attacker knows they are the same?

I want to store two ciphertexts inside the same file. The data stored in each ciphertext is the same (except for padding), but the data was encrypted with different keys and IVs. Both ciphertexts were ...
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Simon's quantum algorithm for symmetric encryption

Though there are many papers available on application of Simon's algorithm for symmetric encryption, nothing is clear on implementation - like how to build the oracle, how many PT-CT combinations are ...
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Private key encryption based on NP-complete problem

Over a decade ago, a question was asked on Stack Overflow, which basically asked if there were any encryption schemes that are reducible to an NP-complete problem, in the sense that breaking the ...
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Do we want to allow/Have we allowed parallelization (e.g GPU programming) to enter the cryptographic field? What are the consequences?

With the term GPU programming, I'm referring to highly parallelizable computing in general. Lastly, I have built a bit of a background in cryptography. So I have started to wonder if/where GPU ...
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Asymmetrical scheme: insecurity concerns of saving a hash of a hash of a password

please verify or explain how to do this properly. I'm letting a user create keys from the client through a secure server. I ask the user for a password on the client, then send the hashed password to ...
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Why do we need to use Asymmetric cryptography if Diffie-Hellman solves the key exchange problem of symmetric cryptography?

I am new to cryptography and I cant get my head around this issue: If symmetric cryptography is faster then asymmetric and given that Diffie-Hellman key exchange algorithm allows you to exchange keys ...
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Sending encrypted message without public key from recipient (elgamal)

assume Bob and Alice use Elgamal encryption scheme. Alice wants to send Bob a message, but does not know Bobs public key. Is there a way for Alice to find out Bobs public key by receiving multiple ...
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How to use symmetric encryption on 1on1 and group chat messenger?

Hi everyone so currently I'm trying to learn about encryption to build secure messaging app (Mobile-app, flutter based). I want the app to have 2 messaging features which are 1 on 1 messaging and ...
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Symmetric encryption algorithm based on multiplication

I've been wondering about this paragraph for some time: Multiplication is a great mixing function. If you work out what multiplication looks like in terms of ANDs and XORs it becomes apparent how ...
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Can a digital signature be used to generate a key for AES encryption?

I am looking to see if using a digital signature is a secure and reasonable way to generate a key for AES encryption. To flow would be as follows: A user signs a message ...
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Encrypting with one key and decrypting with a related key

Given $n$-bit block cipher $E$ (and its inverse $E^{-1}$), define block cipher $E^\prime_k(m) = E_k(E_{f(k)}^{-1}(m))$ where $k,f(k) \in \{0,1\}^n$ and $\forall k:f(k) \ne k$. Under the ideal block ...
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$t'$ parameter in XSL Attack

In XSL Attack, $t'$ parameter can be defined as "the number of monomials in the S-Box equations to be used in $T'$ method" Without taking into account the arguments about the attack, how can ...
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Why some people said we should use Asymmetric key to cipher the weak Symmetric key?

I heard from some people that create a software licensing. They need to generate a short license number format. So if they use RSA (Asymmetric) they will got long key. Also if they use AES (Symmetric)....
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Connecting, joining or merging Substitution Permutation layer

I am trying to identify how the SP Network is constructed. I am looking for plausible solutions that help to connect these layers together and what are the ways that exist in literature other than Kam ...
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Security analysis of North Korean block cipher Jipsam1

The cipher is a modification to AES and is described on this website: The only difference between Jipsam1 and AES-256 is the S-box. Whereas in AES the S-box is public and constant, namely $$ \begin{...
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gpg symmetric encryption decrypts without asking for the symmetric key when --decrypt option is used

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How to ensure files on client computer haven't been tampered with by client?

I'm designing a program that clients can download to the computer. This program needs to sync with my online server on a regular basis to confirm that the client's Activation Code hasnt expired and ...
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If the symmetric key is stolen; can I key revoke without reencrypted data?

I have a question about database security. This is a scenario I have. The data is encrypted using symmetric (i.e., AES) and stored in a database, while the secret key is stored on the client side, so ...
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How much time do commodity computers spend doing bulk data (en)(de)cryption on average?

With the proliferation of https, and one of the primary functions of my pc being browsing the intarwebs, it occurs to me that my cpu is spending a lot of cycles doing AES en and de cryption. For the &...
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Is it possible to calculate the plaintext length of an RC5-32 encrypted ciphertext?

Calculating the RC5 encrypted size of any data is as simple as rounding up the plaintext length to the nearest multiple of 8. What I'm wondering is whether this can be done in the other direction, to ...
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What is benefit of using substitution before permutation or permutation before substitution in a block cipher?

I am trying to understand the difference between the usage of permutation and substitution in a SP Network. Normally, in ciphers except DES, substitution appears to be done before permutation. But ...
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Can we transform LWE symmetric encryption scheme into a commitment scheme?

In the LWE symmetric encryption scheme, a ciphertext encrypting a message $\mu \in \{0,1\}$ under the secret key $\mathbf{s} \in \mathbb{Z}_q^n$ is $(\mathbf{a}, \mathbf{b}=\mathbf{a} \cdot \mathbf{s}+...
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Indistinguishability of symmetric encryption under CCA

I am learning about symmetric encryption and its security properties. One of the security notion is security against chosen cipher-text attacks (CCA), particularly IND-CCA notion. Under this notion, ...
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Is secure of RC6 cipher consider as weak secure? / how to increase safety in RC6 cipher?

I saw a paper said RC6 cipher is weak and weakness cause of using 'SINGLE CLASS OF WEAK KEYS' What is that mean? and could we solve this problem ? Thank you.
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Standard way to generate pseudorandom bytes on demand

I considered Extendable-Output Function (XOF) with a random seed but it seems I would have to specify the output length at the start and store the entire output. I don't know how many bytes I will ...
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Is it safe to re-use a key with Fernet?

Fernet is a supposedly idiot-proof, AES-based symmetric encryption scheme that was (again, supposedly) carefully designed to avoid any pitfalls that might compromise security. I want to use the same ...
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Baby steps with example, looking for an "AES for Idiots" type of explanation

Countless examples all over on implementation of AES. None of these actually make sense to someone with zero cryptographic or advanced mathematical experience. This => too abstract & technical.....
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Is this construction a OWF?

Given the OWF function $f: \{0,1\}^{2\lambda} \rightarrow \{0,1\}^{2\lambda}$ and the PRG $G: \{0,1\}^{\lambda} \rightarrow \{0,1\}^{2\lambda}$, is the following function $f^*$ a OWF? \begin{align} f^...
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Which block cipher modes are best used in real life situations?

For an exam I'm studying for, I'm wondering what block cipher modes are best to use in certain situations. We learned about these block cipher modes: ECB, CBC, CFB (+ s-bit), OFB (+ s-bit) and CTR. ...
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Objective block cipher round function measures of security

One issue that may arise when attempting to evaluate the security of a round function for a block cipher is that the analysis of the round function does not treat the round key space and the message ...
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TLS 1.3 - Why have no encrypt-then-MAC modes been specified?

I have been scratching my head for a while why TLS 1.3 does not include any encrypt-then-MAC (EtM) modes. All the previous problems in TLS have been caused by MAC then and encrypt. Whereas encrypt ...
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What class of complexity theory does a trapdoor function belong to

Let's suppose we have a protocol X (symmetric or assymetric codec) and it encrypts a message M and the only way to get decode M is to use the hidden information and impossible otherwise to crack. To ...
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Clarification on hybrid encryption vs ECIES vs symmetric encrypt the message and then use assymetric for key

I am trying to understand Hybrid encryption. When I first came across the term I though it is used to describe a scheme where the message is encrypted using a symmetric key, and the symmetric key is ...

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