Questions tagged [symmetric]

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

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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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218 views

Why is possible to encrypt multiple messages within the same stream in AES

I have a standard random key and IV. Then I am creating a cipher using these keys and iv and then encrypt a specific message. Later on, if I try to encrypt another message with the same cipher(which ...
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Fernet symmetric-key encryption

Fernet symmetric-key encryption To encrypt and provide data — e.g. JSON strings in a database — using Python I'm wondering what is a good approach (package) for symmetric-key encryption. The Python ...
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How can we link AES with Elliptic Curve Diffie-Hellman Key Exchange Method

Actually, I am working on a project to combine symmetric and asymmetric cryptographic algorithms. The shared secret key for AES will be generated through the Elliptic Curve Diffie Hellman Key Exchange ...
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Lack of response to CAESAR competition

Why is there so little response (e.g. implementation in crypto libraries, programs...) after the end of the CAESAR competition? As far as I can see, there is no shift from AES-GCM to any of the CAESAR ...
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621 views

What is the mainstream cryptography?

I am always hearing the term "mainstream cryptography", I am looking forward to more clarification on this concept. What I the mainstream cryptography? Is its definition subjective? Is ...
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Is it possible to use HKDF in the TPM? [migrated]

Is it possible to use HKDF in the TPM? My goal is to load in a master symmetric key and derive keys from that using HKDF. I see there are other KDF functions available, but no mention of HKDF.
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Have the automorphism groups of block ciphers like the different version of the AES or DES been calculated?

Suppose that $F:K\times X\rightarrow X$ is a function. If $k\in K$, then let $F_{k}:X\rightarrow X$ be the mapping defined by letting $F_{k}(x)=F(k,x)$ for each $x\in X$. Then we shall call $F$ a ...
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Don't human generated passwords used with key derivation functions reduce the security of symmetric encryption?

The key size for AES is chosen as 256 because that's considered the minimum keysize which can protect against a brute force attack - i.e. $2^{256}$ tries. However, in practice, for a lot of ...
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Getting the plaintext encrypting the ciphertext

Context: an encryption game from overthewire (the link to it: https://overthewire.org/wargames/krypton/krypton6.html, also good for more info) where given the ciphertext, one must obtain the plaintext....
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Using two keys and two messages

Is the following cryptosystem possible: There is an encryption function: encrypt (k1, k2, T1, T2) = M, where T1, T2 - two plain texts, with the same number of characters, k1, k2 - encryption keys of ...
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Authentication by Presenting the Symmetric Key over an Encrypted Channel

I have devices which need to communicate with a server over a mutually authenticated and encrypted channel. Authenticating the server is relatively easy, since I can embed the CA certificate in the ...
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Designing a CRAM protocol for mutual authentication in constrained devices

We are currently designing a simple Challenge-Response Authentication Mechanism (CRAM) protocol based on symmetric cryptography that would be used on the constrained embedded devices that would ...
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How many keys are used in symmetric, asymmetric, and hybrid encryption?

There are 8 people in total working on a project. Each one of them will send information to the rest of the team individually 2 times a day. They use 6 days in total for this project. Cryptosystem 1: ...
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Is it practical to build a symmetric encryption cipher that needs the changing of the "main" key for each plaintext?

I read about an encryption cipher that needs the changing of the "main" key for the encryption of each plaintext. Sometimes this change depends on the plaintext and is done automatically. ...
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Are there any estimates for the spectral radius and distribution of eigenvalues for the AES, DES, etc round functions?

Suppose that $F:K\times X\rightarrow X$ is a function such that for each $k\in K$, the mapping $F_{k}:X\rightarrow X$ defined by letting $F_{k}(x)=F(k,x)$ is a bijection. Suppose that $F$ is the round ...
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How to calculate a common encryption key between sender and receiver

In the picture below, for the text underlined in red color: 7X(MOD 11) = 72(MOD 11) =49(MOD 11) My questions are: (1) obviously there is no equal relationship between 72(MOD 11) and 49 (MOD 11), and ...
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36 views

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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825 views

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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50 views

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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59 views

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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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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