Questions tagged [symmetric]

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

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How to properly guarantee authentication, confidentiality, and replay-resistance for multiple messages using a pre-shared key?

I have a device that needs to communicate with another host and exchange fixed-length messages. All traffic should be encrypted and authenticated, and it should be resistant to replay attacks. ...
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Cons for stream ciphers that are based on hash functions

In an answer of here someone mentions: if you have a hash-function-with-oracle-powers, then it is rather easy to generate a pseudo random stream from a secret key, by hashing K||n where K is the ...
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Do groups generated by round functions generate the alternating group?

Let $K,X$ be sets and let $F:K\times X\rightarrow X$ be a function. For each $k\in K$, let $f_{k}:X\rightarrow X$ be the function where $f_{k}(x)=F(k,x)$ whenever $k\in K,x\in X$. Assume that each $f_{...
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is $F_{k_{1}}(m)||F_{k_{2}}(F_{k_{1}}(m))$ always a PRF? when F is a PRF

is $F_{k_{1}}(m)||F_{k_{2}}(F_{k_{1}}(m))$ always a PRF? when F is a PRF As an intuition it seems to me that the answer is "NO" as the two halves of the output depends on each other
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Key Encryption: Does it need to be Authenticated?

Alice wants to store files $m_i$ on Bob's untrusted cloud storage platform, with the additional restriction that she can only store one master key $k$ herself. She encrypts the files with keys $k_i$ ...
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Is PRF XORed with its key still a PRF? (always)

$\forall k \in \{0,1\}^n,m \in \mathbb{M},F_k(m)$ is defined as follows: $F_k(m) = F'_k(m) \oplus k$. It is known that $F'_k$ is a PRF. Note: 𝕄 is the message space and it's assumed that the key $k$ ...
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Is the following derived MAC where the output is XOR'ed with the key secure?

Hey I'm wondering if the following scheme is secure or not , I tried reductions and some tries to prove that it not must be secure but I feel completely stuck . More details: It's just any reduction ...
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Proper implementation AES-256 for single block E_k then being used on AES-GCM

My first objective is to implement AES-GCM in PowerShell 5.1 since there is not an implementation that not use external dll libraries. According to the GCM schema of encryption: the E_k block should ...
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A few questions regarding the 4-Round AES-Distinguisher (by Gilbert and Minier) and DS-MITM

I am struggling to understand the DS-MITM attack on AES (Original Paper). Especially the 4-rounds distinguisher by Gilbert and Minier (section 3). I get the basic idea that we check exactly on which ...
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CPA Security vs Multiple Message Secrecy

In chapter 3 of Katz Textbook, there is a theorem which states as follows: "Any private key encryption scheme that is CPA-secure is also CPA-secure for multiple encryptions." I can make ...
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Is the polynomial system representation of a symmetric cipher overdetermined?

Is the representation of the polynomial system of a symmetric cipher overdetermined?
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LR Oracle for CPA Security for Multiple Encryption

How does LR Oracle model help achieve the CPA security for Multiple Encryption. I am not able to understand how LR oracle model gives an advantage over the normal encryption oracle.(Reference to ...
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Is it possible to crack AES-256 ECB when provided with the ciphertext and a portion of the corresponding plaintext? [duplicate]

AES-ECB encrypts the message by breaking it into blocks and encrypting them one by one. Provided the knowledge of the ciphertext, a portion of the plaintext that corresponds to a block in the message, ...
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Targeting integer number of right pair in differential attacks

As we know, purpose of attackers is finding some high probable differential characteristics in differential cryptanalysis. Then they construct some plaintext structures, plaintext pool and expect some ...
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Role of AND operation in FHE, MPC and ZK

Going through LowMC, one of the main advantage of it seems to be useful in Fully Homomorphic Encryption (FHE), Multi-party Computation (MPC) and Zero Knowledge (ZK) proofs. I have no idea about any of ...
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How does a forward search attack work? [duplicate]

I just came across this term “forward search attack” while reading about Interchange key and Session key. The book mentioned that using session key helps to prevent attacks such as forward search ...
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Fixed size output hash from varying input

To begin with I need to say I have no experience in cryptography (I'm a software developer) and found this place trying to figure out how to solve this, Here is the problem I need to solve in my job: ...
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Proof that the cardinality of the cipher text set is greater than or equal to the cardinality of the plaintext set for a symmetric cryptosystem

I have been working on this problem and would appreciate some help Consider a symmetric cryptosystem with non-empty finite sets $P, C, K$ of plaintexts, ciphertexts, and keys, respectively and with ...
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Verifying affine spaces in Xoodoo component

I am reading "The design of Xoodoo and Xoofff". On page 13 there is a collorary related to the component $\chi$ [Algorithm 1, 1]. Corollary 1. For fixed (difference or mask) $a$, the ...
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What does a linear function with huge order mean?

I am reading this paper "Farfalle: parallel permutation-based cryptography", and there are some terms that I do not understand. Page 4 says ratio efficiency vs. safety margin. What does ...
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AES-128 CBC encryption : ciphertext size seems too large

I am trying to encrypt messages with the AES symmetric algorithm using C language. I am using a key, an Initialization Vector (IV) and a plaintext, all with a length of 16 bytes. I expected as output ...
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Should I encrypt the signature along with the message? [duplicate]

Given that A wants to send a message M to B, I have 2 scenarios as shown: The difference between the 2 is that for case 1, the digital signature is appended to the message before being encrypted ...
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Strategies to address an immutable key in a symmetric cryptosystem

I have a power constrained environment where I do not have enough power to update an encryption key. For this reason, the symmetric key will be programmed before the devices are distributed, and this ...
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Why is the market for cryptographic primitives non-commercialized?

There are not many successful companies in cryptographic primitives market. Certicom holds many patents attached to the ECC. RSA Security probably made some profits from the patent. Are there more ...
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How useful is proxy if we use a symmetric key?

I am trying to understand the proxy re-encryption scheme. In proxy re-encryption: (1)Alice use AES key to produce the symmetric ciphertext of her message. (2)The proxy encrypt symmetric ciphertext ...
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Using $key^{th}$ multiple of $\pi$ as a one-time pad

With a key $k$ of sufficient length, say 128 bits, is it possible to use $k^{th}$ multiple of $\pi$ as a one-time pad? Please enlighten on the security as well as practical aspects (only if secure of ...
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How exactly to concatenate two differential trails to form a boomerang disguisher in practice?

I've been reading many papers on boomerang/rectangle attacks. The general strategy is to find two trails for a small number of rounds and then concatenate them to form a longer distinguisher. ...
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Implement deterministic authenticated encryption using libsodium

Note: this is my first question on stack exchange, let me know if you miss some details to answer and I will edit the question accordingly Context I'm willing to create a git encryption tool (...
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1answer
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How to calculate the branch number of a linear mapping?

Is there an efficient algorithm which can be used to determine the branch number of any given linear mapping?
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Enigma Machine rotors math

I have been doing a study about the enigma machine for the past weeks. I managed to get ahold of the formulae used in "Cryptography, Information theory and error-correction" book for the ...
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1answer
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How do we know a single differential/linear trail dominates the others?

I have read the proof of AES's resistance against differential cryptanalysis. In the proof the authors show that there is no single differential trail with prop ratio higher than $2^{-300}$ over 8 ...
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Is there any standard present to measure strength of a generated key using true random number generator?

I was wondering how to measure the security strength of a generated secret key for the below protocol: "A 128 bit random number is generated by TRNG and the random number will be used as a ...
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Add setup to GPG symmetric

I use GPG symmetric, to encrypt text file. Is it possible to use GPG symmetric, to encrypt a text file, and at the same time, add additional setting to the encrypted file, to give us 2 conditions: ...
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Encrypting h(k) for defeating partition oracle attacks

Is encrypting $h(k)$ (or even just $k$) and verifying it before checking the MAC enough to defeat partition oracle attacks and thus make the whole scheme robust/committing (without depending on ...
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Number of bit operations required for encryption in a Block cipher

I want to find out how many bit operations are performed for encryption in AES-128 with messages size $128$ bits. For public key encryptions such as RSA and ElGamal, I know that number of bit ...
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What symmetric algo does TLS use?

So my understanding of TLS is that it uses asymmetric cryptography such as DH to perform a key exchange, once this has occurred it then used an symmetric algorithm for the data exchange. (Obviously I ...
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nonlinearity and autocorrelation of common s-boxes

I cannot find publications comparing the properties of popular cipher s-boxes. First of all, I am interested in nonlinearity and autocorrelation of s-boxes, which are used in seed, cast-128, camellia ...
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Is there an algorithm that gives a reasonable chance of decoding the entire ciphertext of this encryption scheme?

Suppose Alice and Bob share two $n$-bit shared keys, $k_1$ and $k_2$, and decide to send multiple $n$-bit messages to each other. The encryption scheme they use simply sends $c_i = (k_1 + i k_2) \...
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Can any message be decrypted using a given ciphertext and an appropriate key?

Does the following proposition hold for any deterministic, symmetric cryptosystem $(\mathcal{M}, \mathcal{C}, \mathcal{K}, Enc, Dec)$? $$\forall C \in \mathcal{C}: |\{M'| \exists K \in \mathcal{K}: ...
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Where is the SIV in AES-GCM-SIV?

This is my understanding of Synthentic IVs You have 2 keys $K_1$ & $K_2$. $F$ is a PRF Instead of choosing a separate IV, you instead generate the IV from the PlainText. $IV = F(K_1, m)$ $c = E(...
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Brute force strategy

I am a beginner in this field, and I was thinking about brute force strategies to break symmetric key encryption. Let's say we have a block cipher in CTR mode and the key is 56 bits in size. What ...
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Question about IND-CCA security

We are given the following securitygame $G^{\text{LOSTNAME}}$: Generate $k \leftarrow \{0,1\}^{\kappa}$ uniformly at random Choose $h \leftarrow \{0,1\}$ uniformly random Create decryption oracle $\...
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Encrypting a broadcast message decryptable by a subset of receivers

I wasn't certain how to title this request/problem, but here goes: I'm A, and I want to send a message that is received by B, C, D. Each receiving entity here is part of some set of domains D1, D2, D3:...
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Modular Addition in RC5 is linear or not?

So, far my understanding was Modular addition is non linear function which is mainly used in ARX based ciphers. While I was glancing through RC5 paper (https://link.springer.com/content/pdf/10.1007/3-...
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Symmetric key as proof of ownership of a session?

I have a question, or rather multiple questions that all relate to the same topic. I am building an application with both a frontend (FE) and a backend (BE). All communication between FE and BE is ...
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Could a symmetric encrypted communication with a SHA-512 hash still be manipulated?

I just got back from an exam review and there was a question I remembered that I apparently got wrong. I wonder if someone could help me with this, since it bothers me. The question was something like ...
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Encryption on one AES mode and decrypting on another, where both use HMAC

Let's say there are 2 ciphers, $enc$ and $dec$, where: $enc$ will encrypt the data, and $dec$ will decrypt it. Both $enc$ and $dec$ must be an AES cipher. $enc$ and $dec$ will use the same key $k$ ...
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Mathematical and empirical analysis of AES

Hello everyone and happy new year in advance. I'm doing a work about the analysis of the AES algorithm, and I have some doubts about this. First, I need to do the mathematical analysis of the ...
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Is CTR more secure than CBC?

In cryptography, a block cipher mode of operation is an algorithm that uses a block cipher to provide information security such as confidentiality or authenticity. A block cipher by itself is only ...
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Key storage management of session keys and long term keys

In key management, one of the topics is key storage, I want to know where and how these keys(long-term and short-term) are stored? For example I read that android password apps use KeyStore api to ...

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