Questions tagged [symmetric]

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

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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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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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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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Proof that in a perfect cipher the key must be unique

Can someone give me a hint about how can i prove that if i have a (Shannon) perfect cipher then it must be that the key $k$ that $\text{enc(}k, \text{message) = ciphertext}$ is unique.
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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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Encryption in SET protocol

I have a rough idea of what is symmetric and asymmetric encryption, but I can't apply the idea to the SET protocol (Secure Electronic Transaction Specification), so how the symmetric and asymmetric ...
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Symmetric Exchange Key Sharing

Question: Suppose that there are 10000 = 10^4 banks and 10 payment card organisations (PCOs). How many secret keys will be needed if each PCO shares a unique secret key with each bank? How many extra ...
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How is the 'Algebraic Degree' calculated in the paper about analysing the white-box AES(Chow et al. 2002) by exploiting internal collisions?

This paper proposed a new attack on the initial white-box AES implementation of Chow et al. In order to determine the good solution, we use the particular structure of the function $S_{0}$. $S^{-1} \...
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What are the fundamental roots of modern symmetric encryption?

In academic pursuits, we often have people (and their ideas) who are considered fundamental to the subject, such as Bayes and probability. In cryptography, it's obvious to see that the Diffie-Hellman ...
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Zero knowledge proof of symmetric keys and encrypted texts resulting in the same text, if the symmetric keys are encrypted with asymmetric ones

Suppose I have: text T, symmetric keys X, Y encrypted text T with symmetric keys X, Y = TX, TY accordingly asymmetric key Z, used to encrypt X, Y to transmit them to a person. Let the encrypted ...
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IND-CCA secure symmetric encryption

Although this question maybe looks silly, I have searched similar questions in this forum and googled it but got no desired answers. IND-CCA security has already been deeply studied in public ...
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Generation of Rijndael S-box [duplicate]

I'm an electrical engineering student and was doing a brief research regarding the round transformations of the AES-128 and came across the Wikipedia article describing the generation of the ...
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What is most secure way for one party to encrypt 4 bytes in less than 40 bytes, which will be publicly available?

I have a project where a user needs to store a U32 encrypted on a blockchain such that they can recover it themselves: the user will always have their key available but may "forget" the U32 ...
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Designing a simple challenge-response symmetric mutual authentication protocol

I am designing a protocol that 2 devices will use to mutually authenticate over an unreliable, unsecure channel. The system must be fast and low-power, so symmetric cryptography is a requirement. I ...
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Is Caesar cipher perfectly secret?

The only time a shift cipher considers to be perfectly secure is when used on a single letter of plaintext and no more. Having that in mind, we can say it is certainly not perfectly secure. Caesar ...
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Help needed for IBM KCV

I found old key letters used in EFT HSMs with TDES keys, parted in two halfs. The check value printed on this letters is called IBM CV and doubled IBM CV. My newer HSM does not support this kind of ...
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Best practice for JWE symmetric key encryption

After the user authenticates with Auth0, the backend issues a JWE with some info about the user. I do not want the user to be able to see the payload, which is why want to encrypt it. Furthermore, ...
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Bruteforcing a symmetric cipher [duplicate]

I don't understand how we could bruteforce a symmetric cipher. Let's take AES with a key size of $128$ as an example. It means that there are $2^{128}$ possible keys, and as many ways to decrypt a ...
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Calculating symmetric key bit strength

16 byte key where each byte is in range 0-255, generated using cryptograhic PRNG will be believed to have 128 bit strength. What would be a bit strength of a key generated using same quality PRNG, ...
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Questions about Symmetric Encryption part of TLS

In TLS, we use DHKE for establishing the session key & then encrypt the actual communication with session key using symmetric encryption. While reading about DHKE, I learnt that you could use the ...
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How to estimate the maximum computational cost bound for Key Derivation Functions (KDFs) before it becomes useless security-wise?

From my understanding of Key Derivation Functions (KDFs), e.g. scrypt, Argon2, etc, we can tune their parameters such that it eventually becomes harder for an attacker to brute force a password-to-key ...
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Can Key-Encryption Key (KEK) be symmetric?

This from Cryptography course from Coursera: Key wrapping or encapsulation using a KEK can be accomplished using either symmetric or asymmetric cipher For my information KEK solves the key ...
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What should the nonce value be for client-side encryption?

I am using the following chacha20poly1305 Rust library to encrypt some data in a desktop application. The user provides the key, which never leaves their device, to locally encrypt some data, and then ...
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How to generate the exact AES key in both client and server side?

I am using AES to create a secure tunnel for transmission of data. As the symmetric key encryption will require the same key to encrypt and decrypt, so we need to generate the exact same key for the ...
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regarding usage of hashing

I have a question regarding pitfalls of using only encryption. Suppose Bob and Alice want to flip a coin over a network. Alice proposes the following protocol. Alice randomly selects a value X ∈ {0,1}...
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Matrix cipher - symmetric or asymmetric cryptosystem?

Matrix cipher is defined by: a) Encryption: $C = K \times Z$, where $C$ is a cryptogram vector, $Z$ is a message vector and $K$ is encryption matrix (encryption key) b) Decryption: $Z = K^{-1} \times ...
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Proving security of $\Pi' = E_k(E_k(m))$ knowing $\Pi = E_k(m)$ is secure

I recently started studying cryptography but I am not sure I quite understand the concept of proof by reduction. Question I am trying to solve is as follow: Suppose $\Pi$ is a symmetric encryption ...
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Is it safe to use RSA multiple times

Assuming I have multiple symmetric keys on specific machine(more than 10000 probably), can I use the same rsa key to encrypt all of those keys? I'm a bit concerned from a situation where multiple ...

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