Questions tagged [symmetric]

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

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Do I need to use unique IVs if all encrypted data is unique?

I am designing a service where each user has both a unique 256-bit private and public ID. These IDs should be derivable from one another, but only within the backend of my service (as to not expose ...
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Is a Shift Cipher with Random Insertions Unbreakable?

Imagine an Encryption Algorithm which applies a classic Shift Cipher (also called Caesar or ROT-X) to a text (with only lowercase [a-z] and the space ...
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Are semantic security and indistinguishability equivalent for symmetric key cryptosystems?

I've seen a lot written about how, in the context of public key cryptosystems, these definitions are equivalent. Is the same true of symmetric key cryptosystems? If so, what are the precise statements ...
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Does this protocol description and design look sound?

I am working on a tool that uses password derived keys for AES and a selectable modes of operation to encrypt (and later decrypt) text for storage on an insecure media. The tool is constrained to ...
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Web app server side encryption scheme

I'm asking if this encryption scheme would increase the security of the user's data. Here's how it would work: The user would create an account (username + password). An encryption key (symmetric) is ...
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Shared Key message-encryption multiple receiver communication

Say there are 5 parties. 1 is the sender, and 4 are the receivers. The sender has a unique shared key with each receiver. k1 - between sender and receiver1 k2 - between sender and receiver2 k3 - ...
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In Symmetric encryption where Alice and Bob message each other, how can both decrypt the same data?

I first posted this question on StackOverflow but they told me it belongs here instead: https://stackoverflow.com/questions/77856486/in-symmetric-encryption-where-alice-and-bob-message-each-other-how-...
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How does SMB authentication work?

When I learned about the inner workings of the TLS protocol and what exactly it protects a connection against, I was surprised to learn that even asymmetric encryption can be defeated by a MITM attack ...
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Key-dependent cipher generation

Is there any cryptanalysis possible if the cipher itself is deterministically derived from key material? For example, suppose you have n building blocks (ARX primitives, AES ops, other primitives) and ...
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Security of this MAC scheme

I'm studying for a cryptography exam, I have this question from a past exam: Consider the MAC with key $k$, based on a block cipher $E_{(k)}$ with block size $n$, and a collision-resistant hash ...
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Is plaintext and ciphertext absolutely one-to-one in symmetric encryption algorithms? [closed]

Known conditions: The block size of this algorithm is 16 bytes. If there are multiple encryption modes, then it is limited to ECB mode. Always use only one immutable key. Since only ECB encryption ...
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The security of cyclic affine key schedules

Suppose that $k$ is the key for a block cipher. I am interested in the security of key schedules of the form $(k_0,\dots,k_n)$ where $k=k_0$ and $k_{j+1}=A_jk_j+b_j$ where each $A_j$ is some constant ...
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Can the requirement to increase rounds with key size be bypassed?

When taking AES for example, the number of rounds increases as the key size increases. This is done in order to adequately diffuse key bits into the state of the cipher. Suppose you replace the AES ...
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How to evaluate the minimum complexity of the key recovery when the success probability p is given?

Since the practical security of a symmetric-key primitive is determined by evaluating its resistance against an almost exhaustive list of known cryptanalytic techniques. My problem is that could we ...
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Does something like Symmetric reencryption exist?

I'm an amateur so bear with me. I was thinking about an E2E solution for data-at-rest proxy scenarios (like cloud storage provider) that allows you to issue and revoke users via symmetric keys. I'm ...
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Why does symmetric encryption not provide authentication and integrity? Is it only this type of encryption or cryptology in general have this issue?

Studying for Cryptology and came across a presentation regarding on "Integrity vs Authenticity" where the discussion briefly mentions how Encryption "does not provide integrity or ...
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Why KeePassXC is deriving (stretching) the key again before saving changes to the database?

KeePassXC supports Argon2, which is great for security. However, there's a quirk that's been bothering me. Every time I save modifications to the database, it seems to stretch (derive) the key again, ...
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For Symmetric Cryptography, why is it considered more important to safeguard a key than the function/algorithm for encrypting/decrypting a message?

As stated for the question above here's an analogy: You are a robber looking for a house to rob with two different scenarios that might occur. 1. You have a key that you know belongs to a house and ...
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Does ISAAC really guarantee a cycle length of at least 2**40?

I just noticed that the FSE 1996 conference paper which defines ISAAC mentions a counter variable cc. This variable is said to be the reason why ISAAC has a ...
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Is ISAAC+ actually an improvement over ISAAC?

I just tried to implement ISAAC from scratch, using the Jean-Philippe Aumasson paper from 2007 as a reference. This paper gives a definition of the original ISAAC algorithm as well as the improved ...
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How secure is a file encrypted with GnuPG, a strong passphrase, and the symmetric option?

Suppose I encrypt a file, of, say, 10 MB, with a secure, suitable passphrase, and the command: gpg --symmetric my_file.txt What level of expertise and hardware ...
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symmetric key generation - random number vs pbkdf2

I am working on improving my grasp on applied cryptography. Following question is just for learning/understanding purposes.. Lets say I want to generate a 16 byte key that I want to use for some ...
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Does any encryption/decryption algorithm supports linear decomposition?

I am not sure whether "linear decomposition" is appropriate to summary my question: We know that the traditional symmetric encryption/decryption algorithm (like AES, TDES) can be written as: ...
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Safe implicit value validation: $H_k(k \oplus m) \sim H_k(m)$?

$H_k$ is a cryptographic hash function that's keyed using a section of key material $k$ (for whatever definition of "keyed" that's appropriate for the given hash function $H$). Are the ...
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Can I predict CryptGenRandom on my own device?

I have a Windows 10 laptop with an algorithm that creates a random number using the PRNG CryptGenRandom. According to Wikipedia: Because CryptGenRandom is the de facto standard CSPRNG in Win32 ...
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Given $i$ keyed-$PRP$ labels $\ell_{i,x}$ from a $2^{256} \times 2^{256}$ Sudoku (Latin-square), how difficult is it for an adversary to solve?

There's a keyed-permutation I'm playing with, $\ell_{i,x} = \pi_i(x_i)$, which is a bijection $X \leftrightarrow X$, where $|X| = 2^{256}$, and whose evaluations on plaintext inputs $x_i$ perfectly ...
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Securing symmetric ciphers with 56-bit keys

Under the Wassenaar Arrangement and applicable export control law, symmetric cryptography of an (effective) key size of 56 bits or less is (generally) exempted from export control. I am forced to work ...
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Fully-encrypted (non-fingerprintable) symmetric encryption algorithm?

I am a student in the process of creating a firewall circumvention program based on smuggling data inside of legitimate HTTP. I have limited cryptographic knowledge. I need a way to encrypt my higher-...
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Derrive a new key from Trusted Third Party (e.g. Kerberos) session key

Kerberos (and I assume other Trusted Third Party protocols) use (hash) an existing shared secret key to create a session key used for authentication. I read that this authentication secret key can ...
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How to write monomials in $GF(2^n)$ as a system of equations in $GF(2)$

Let $F = GF(2^n)$ and $P(x) = x^e, P : F \rightarrow F$ be a monomial of degree $e$. How to write each bit of the output of $P$ as a function of input bits? In other words, how to write it as a system ...
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Linux Kernel CryptoAPI key exchange and key derivation

I have a custom network and I want to implement a symmetric key exchange and key derivation mechanism with ECDH. I know that I need to use KPP API and ECDH helper functions, but I can't find any code ...
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Symmetric and asymmetric encryption using the same encryption/decryption algorithm?

If we use the following notation: $$C = E(P, K_e)$$ $$P = D(C, K_d)$$ Where: $$E(), D(), C, P, K_e, K_d$$ are the encryption algorithm, decryption algorithm, ciphertext, plaintext, encryption key and ...
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How are the iterations of the AES encryption algorithm determined?

All the knowledge I have learned about encryption algorithms tells me that the AES encryption algorithm uses three key bit lengths of 128, 192, and 256 to encrypt data, and these three key bit lengths ...
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Issue with AWS Encryption SDK for JavaScript in Browser: 'Buffer is not defined' [closed]

I'm trying to implement AWS Encryption SDK for JavaScript in a browser environment within a React application. When I attempt to construct an instance of the encryption client using buildClient ...
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AES-GCM for sensitive database field - good solution?

I have been researching the best encryption to use in a .NET application for managing a sensitive database field (column). This encryption is on top of e.g. AWS at-rest encryption applied to the whole ...
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Provably secure cryptography in blockchains

Do you know a blockchain that does not use at all cryptographic primitives standardized by USA or other countries? It is strange to me that the security of many cryptocurrencies is based on ciphers, ...
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Choice of nonce for reproducible encryption

In my application I have an SQLite database that stores labels for images, like this: IMAGE ID LABEL 1 foo 1 bar 2 bar 3 foo The LABEL column is indexed as it is important that I can efficiently ...
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Does triple ChaCha20 have 256-bit post-quantum security?

Experts suggested 3DES when AES wasn't developed yet, since meet-in-the-middle attack, they suggested triple DES. Grover's algorithm, a quantum algorithm, weakens symmetric encryptions, how about ...
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Is a pseudorandom function (PRF) also a one-way function (OWF)? If yes, how can we proof that a PRF $f_k$ is a OWF? If no, what is the closest work?

Let $f_k$ be a PRF. We claim that $f_k$ is a OWF. PROOF let $f_k$ is not a OWF, there exists a $PPT$ algorithm $A$ that can invert $f_k$ with non-negligible advantage. Even if we know the input $x$ ...
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Deriving secret keys vs generating and encrypting them

Suppose one has a password manager, based on symmetric cryptography, that requires a master passphrase to be unlocked. Argon2 is used for deriving a secret key from the master passphrase. I need ...
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NIST statistical tests [duplicate]

I'm having trouble testing a not-so-popular algorithm that I haven't found an implementation of, so I wrote it myself and now I'd like to test it with nist tests, but I have a suspicion that I'm doing ...
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Can Quantum Computers crack RSA and AES?

Im trying to learn more about cryptography and ran into a post, Is AES-128 quantum safe?, which asks if AES-128 is safe. From the articles and replies it seems that AES-128 (symmetric key) is safe ...
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Can new decryption keys be issued without modifying the encrypted contents? [closed]

I'm curious if there's an encryption scheme where content may be encrypted to a public key where the associated private key can generate new decryption keys for the same content. The goal is to ...
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Resistance against timing attacks of AES candidates

It's difficult to implement AES securely and efficiently if the adversary can observe the timing and (approximate) location of memory accesses, unless you have dedicated hardware. The naive ...
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In AES, why do we multiply the columns by a polynomial with a repeating coefficient?

In the MixColumns step of AES, one multiplies each of the columns of the $4\times 4$ box of bytes by the polynomial $a(x)=\{03\}x^3+\{01\}x^2+\{01\}x+\{02\}$ (modulo $x^4+1$). But in this polynomial, ...
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Age: stream cipher with public key cryptography?

I have some rudimentary cryptography knowledge but am by no means an expert. I generally understand stream ciphers, such as such as ChaCha20-Poly1305, to be symmetric. I am wondering how age (https://...
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Do multiple keys mitigate Grover algorithm?

Grover, a quantum algorithm, weakens AES and ChaCha20. Is it possible to use multiple symmetric keys to encrypt a message multiple times to achieve 256-bit security for quantum computers?
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What kind of symmetric key ciphers are secure thanks to the intrinsic cryptographic method instead of making the key length very long and secure?

For example, Threefish has a key length of 1024 and a very long number of rounds (80). but, I have not heard much about Threefish-1024 being particularly secure, so what symmetric key ciphers are ...
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How does AES-CBC encryption achieve non-repeating blocks of ciphertext?

I am very interested in encryption algorithms, especially AES encryption algorithm in symmetric encryption. To this end, I have studied a lot of theoretical knowledge about AES encryption algorithm ...
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What is the most secure hybrid cipher suite(Library) possible today?

What combination of public key cryptography (DH) and symmetric key cryptography is currently available that is (subjectively) as secure as possible over other ciphers (AES,curve448) when security is ...
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