Questions tagged [symmetric]
Symmetric cryptosystems assume two communicating entities share a pre-established secret key.
705
questions
1
vote
1answer
31 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. ...
1
vote
2answers
781 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 ...
1
vote
1answer
38 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_{...
2
votes
0answers
34 views
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
1
vote
1answer
72 views
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 $k_i$ ...
3
votes
1answer
67 views
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 $k$ ...
2
votes
0answers
81 views
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 ...
0
votes
0answers
32 views
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 ...
0
votes
0answers
28 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 ...
4
votes
1answer
174 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 ...
2
votes
0answers
28 views
Is the polynomial system representation of a symmetric cipher overdetermined?
Is the representation of the polynomial system of a symmetric cipher overdetermined?
0
votes
0answers
15 views
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 ...
1
vote
0answers
16 views
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, ...
0
votes
2answers
42 views
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 ...
2
votes
2answers
93 views
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 ...
0
votes
0answers
26 views
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 ...
0
votes
1answer
34 views
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:
...
1
vote
1answer
49 views
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 ...
2
votes
0answers
17 views
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 ...
2
votes
2answers
85 views
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 ...
0
votes
1answer
51 views
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 ...
0
votes
0answers
36 views
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 ...
0
votes
1answer
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 ...
14
votes
3answers
4k views
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 ...
0
votes
0answers
24 views
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 ...
3
votes
2answers
82 views
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 ...
3
votes
1answer
78 views
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. ...
1
vote
0answers
60 views
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 (...
1
vote
1answer
58 views
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?
0
votes
0answers
53 views
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 ...
1
vote
1answer
61 views
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 ...
1
vote
1answer
78 views
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 ...
0
votes
0answers
32 views
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:
...
1
vote
1answer
80 views
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 ...
0
votes
0answers
31 views
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 ...
1
vote
2answers
77 views
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 ...
0
votes
0answers
36 views
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 ...
0
votes
2answers
53 views
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) \...
0
votes
1answer
53 views
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}: ...
1
vote
1answer
101 views
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(...
0
votes
1answer
63 views
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 ...
0
votes
0answers
45 views
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 $\...
1
vote
1answer
32 views
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:...
1
vote
1answer
54 views
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-...
0
votes
1answer
44 views
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 ...
2
votes
1answer
162 views
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 ...
-1
votes
1answer
56 views
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 $k$ ...
0
votes
0answers
79 views
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 ...
0
votes
2answers
206 views
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 ...
0
votes
0answers
69 views
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 ...
