Questions tagged [symmetric]
Symmetric cryptosystems assume two communicating entities share a pre-established secret key.
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Public key stored in PKI [closed]
In a public key infrastructure how does a User A communicate with the user B?
How does user A send his public key to user B ? Where is a public key stored where do they retrieve it from?
This question ...
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1answer
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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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101 views
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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34 views
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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1answer
251 views
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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25 views
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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1answer
45 views
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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28 views
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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2answers
57 views
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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23 views
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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1answer
203 views
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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1answer
146 views
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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28 views
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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1answer
42 views
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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41 views
What are the lower computation and memory cheap fractal symetric encryption algorimths?
Pretty much the title, I would like to know about encryption schemes that is based in Fractal theory, with decent security and pretty fast.
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129 views
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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0answers
57 views
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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54 views
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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1answer
97 views
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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74 views
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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2answers
243 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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1answer
66 views
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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1answer
86 views
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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1answer
133 views
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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2answers
703 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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3answers
83 views
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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2answers
104 views
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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62 views
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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1answer
59 views
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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0answers
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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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4answers
261 views
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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1answer
28 views
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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1answer
37 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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2answers
844 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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1answer
54 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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35 views
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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1answer
219 views
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?
