Questions tagged [symmetric]
Symmetric cryptosystems assume two communicating entities share a pre-established secret key.
683
questions
0
votes
0answers
17 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
65 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
73 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
42 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
47 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
43 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
55 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
65 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 ...
-1
votes
0answers
26 views
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.
0
votes
0answers
23 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
65 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
28 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
70 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
33 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
50 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
51 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
45 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
57 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
36 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
28 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
46 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
40 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
154 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
47 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
69 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
136 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
59 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 ...
1
vote
1answer
22 views
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 ...
0
votes
1answer
62 views
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 ...
1
vote
0answers
33 views
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} \...
0
votes
1answer
81 views
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 ...
0
votes
0answers
21 views
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 ...
3
votes
1answer
126 views
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 ...
1
vote
0answers
52 views
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 ...
1
vote
2answers
425 views
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 ...
0
votes
2answers
117 views
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 ...
6
votes
2answers
5k views
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 ...
1
vote
0answers
37 views
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 ...
0
votes
0answers
20 views
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, ...
2
votes
1answer
248 views
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 ...
0
votes
1answer
57 views
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, ...
2
votes
1answer
94 views
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 ...
2
votes
1answer
138 views
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 ...
3
votes
1answer
122 views
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 ...
7
votes
3answers
1k views
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 ...
2
votes
1answer
903 views
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 ...
0
votes
0answers
113 views
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}...
0
votes
0answers
32 views
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 ...
1
vote
2answers
124 views
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 ...
1
vote
2answers
81 views
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 ...
