Questions tagged [symmetric]

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

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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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Shark cipher SBox

In the literature, I can’t find the S-Box component of SHARK block cipher. I appreciate if anyone help to find the elements of the S-Box of this cipher.
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Seeking symmetric encryption algorithm optimized for short and human readable ciphertext

In my application, the user logs in when connected to the central database, and their login credentials are authenticated against that data and cached (encrypted). Then, when the user is offline, ...
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INT-CTXT game adversary

I am trying to answer this question. But I think I got it wrong. I am not sure why and how I can improve it. This is the adversary I came up with. Is this correct? ...
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Timing attacks: Symmetric vs Asymmetric Algorithms

There is a statement that I can't give a reference; "Since the timing characteristics of symmetric algorithms are not as key dependent as asymmetric algorithms, they are more resistant against ...
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What are security reductions of symmetric-key algorithms?

I was reading Wikipedia page of post-quantum cryptography. It says that it is desirable for cryptographic algorithms to be reducible to some particular mathematical problem, that is intractability of ...
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What are the misconceptions of IBM's CEO Arvind Krishna talk on the "Axios on HBO" about the quantum computing

IBM CEO Arvind made a talk in HBO's Axios program. It seems that there are misconceptions/misleading/flaws in reasoning etc. What are those! Some of the details of the speech is given as; IBM says ...
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Equivalent conditions for perfect secrecy of a symmetric crypto system

I've been reading about perfect secrecy in crypto systems and I've ran across two definitions which turn out to be equivalent. The first is Shannon secrecy: A crypto system $(\cal K, \cal M$, $\text{...
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Can a nonce be completely random on (simplified) Needham–Schroeder Protocol?

From what I've read so far, nonces are random one-time values, which are sent in plaintext in addition to the ciphertext to verify identity of sender/receiver. Theoretically, if the nonce is random, ...
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Perfect secrecy of the reverse of a crypto system that has perfect secrecy

I am trying to solve a problem that reads as follows: Let $E_1 = (\text{Gen}_1, \text{Enc}_1, \text{Dec}_1)$ be a crypto system that has perfect secrecy. Denote the message space $\mathbb M_1$, the ...
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What are the lower computation and memory cheap fractal symmetric encryption algorimths?

I would like to know about encryption schemes that are based in Fractal theory, while they have decent security and are pretty fast.
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Is Diffie-Hellman Key Exchange an Asymmetric or Symmetric Algorithm? [duplicate]

To my understanding, the DHKE algorithm is symmetric since it only produces a shared secret, rather than public and private keys, however googling "is diffie hellman asymmetric?" results in ...
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How to interpret my professor's statement about "seed" and "symmetric-key encryption"?

In the cryptography course, the professor said that: these days for symmetric key encryption, instead of sending out the key, Alice sends the seed to Bob, and then based on that Bob can get the key. ...
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What would be an O(n) time adversary for this kind of scheme

Suppose we have a block cipher $$E:\{0,1\}^k \text{ x } \{0,1\}^{2k} \rightarrow \{0,1\}^{2n} \quad \text{ with } \quad k,n\geq128$$ K is the key generation algorithm that returns a random k-bit key. ...
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Decrypt one cipher with multiple and independent passwords

Consider that an online shop subscribes an embedded external service for their customers. This external webpage is accessible through a clickable banner on the online shop. On the subscription area of ...
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Possible for a different key to decrypt properly?

I am thinking about CPA-security for symmetric encryption. So $A$ gets access to an encryption oracle, and it can keep asking queries (training phase). In this training phase, he asks $m_i$ and ...
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Encrypt/Cipher and Decrypt/Decipher a string with a secret

In developing an app I have a simple use case in where I want to encrypt/cipher a string (it could also be a couple of bytes because it's essentially just an IP-Address). On the output I think it ...
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