Questions tagged [symmetric]
Symmetric cryptosystems assume two communicating entities share a pre-established secret key.
0
votes
0answers
51 views
Key Reduction in symmetric cryptography [on hold]
The number of keys in a system with $n$ users where every possible pair of users desire to securely communicate between themselves using symmetric cryptography is $n(n−1)/2$.
Is there a way to reduce ...
0
votes
0answers
27 views
Difference between Sibling Intractable Function Family and Secret Sharing? [closed]
What is the difference between any Secret Sharing Scheme Link and Sibling Intractable Function Family (SIFF) Link?
1
vote
0answers
22 views
How does the key agreement process take place in Virgil E3Kit SDK for end to end encryption?
I'm using Virgil E3Kit SDK to implement end-to-end encryption in my App. Their E3Kit SDK is very effective and not too hard to understand, but I still don't understand how does the key agreement ...
3
votes
1answer
78 views
Zero-knowledge proof with only a ciphertext
Suppose there is a plaintext p, which is encrypted with a symmetric cipher using a key k, resulting in a ciphertext c. Bob knows both c and k, but Alice knows only c. Is there any protocol by which ...
3
votes
1answer
60 views
What does it mean : “Canonical representative of Sbox is 0123468A5BCF79DE”? and How can we calculate this representative for Sbox?
In paper :Cryptographic Analysis of All 4 × 4-Bit S-Boxes Saarinen has classified $4 \times 4$ S-Boxes and defined Canonical representative for each class of S-Boxes.
What does "Canonical ...
6
votes
1answer
3k views
AES: Why is it a good practice to use only the first 16 bytes of a hash for encryption?
I'd like to encrypt Text with AES/CTR and a password defined by the user in java. I already checked the internet (and stackoverflow) for answers. The most used version is to hash the user password ...
1
vote
1answer
55 views
What is the inverse function of the finite field GF($2^3$) and GF($2^4$)?
I am currently reading a paper Cryptanalysis of a Theorem Decomposing the Only Known Solution to the Big APN Problem. In this paper, they mention that they used $I$ which is the inverse of the finite ...
2
votes
1answer
59 views
What does $x^{1/e}$ mean in cryptography in this open butterfly structure?
I am currently reading a research paper that introduces this thing called a butterfly structure.
I am confused about the structure of the open butterfly in this paper which has the equation $H^{\...
0
votes
1answer
72 views
Reed Solomon secret sharing and as a one-time symmetric key?
Shamir's Secret Sharing is just a special case of Reed-Solomon where only one coefficient is used to store the secret instead of the entire polynomial.
McEliece however, suggests that the latter can ...
0
votes
1answer
27 views
Randomly initialised global counter used to encrypt the kth message with IV = IV + k mod 2^n
The use of an increasing IV is not secure for a block cipher. That is, using a random IV for the first message then IV + 1 for the second , IV + 2 for the 3rd etc. How can I construct an attack to ...
3
votes
1answer
300 views
Is there a symmetric-key algorithm which we can use for creating a signature?
I know that in the asymmetric-key algorithm the RSA signature exists but what about the symmetrical ones?
0
votes
0answers
46 views
How can a node establish pairwise shared key with other nodes using its own polynomial share together with other's public values?
A server has a symmetric bivariate polynomial $ F(x, y) = \sum_{{i,j}=0}^{t-1}a_{i,j}x^iy^j$ $\in GF(p)[X, Y] $ of degree $t-1$. For simpliciy, $ F(x, y) = a_{0,0}+a_{1,0} x+a_{0,1}y+ a_{1,1}xy$ mod ...
1
vote
1answer
64 views
Find encryption algorithm knowing input, output and secret
Today on my PC I found some old backups; they contain also some pictures I encrypted years ago with a smartphone running Windows Mobile but I don't remember the application I used to cipher them.
I'm ...
9
votes
1answer
183 views
CAESAR finalists: Lightweight case (Ascon vs ACORN)
The Ascon cipher has been selected as the first choice in lightweight case and ACORN as the second. However according to Face-off between the CAESAR Lightweight Finalists: ACORN vs. Ascon paper, the ...
1
vote
1answer
59 views
OAEP security with variable length hash function
I'm implementing a hobby cryptosystem for fun and to increase my knowledge on the subject, and I was wondering if the OAEP construct was still sufficient as an all-or-nothing-transform if variable ...
3
votes
2answers
815 views
Insecure private-key encryption
I am learning about crytography and the differences between the public and private keys encryption examples and I was wondering if it is possible to have a private key encryption scheme that is ...
3
votes
1answer
73 views
Definition of symmetric cipher and definition of asymmetric cipher
So I'm currently taking a cryptography class right now and my professor has told the class that she can't even define symmetric cipher for us without getting into asymmetric ciphers and the textbook ...
2
votes
2answers
90 views
How does an S-box introduce confusion
I'm trying to find the logic for introducing the S-box, but having trouble understanding why. In a simple cipher, e.g.
c = pt xor key
I understand that I can ...
0
votes
0answers
22 views
What are dual codes and the codewords denoted by these dual codes in terms of trace?
I am currently reading a research paper (linked below) that mentions "Consider only maps that vanish at 0, their short codes $C_f$ and their duals $C_f^\perp$. The duals can be written as $C_f^\perp = ...
1
vote
1answer
37 views
What is the link between the parity check matrix, double-error-correcting codes and APN permutations?
I am currently reading a research paper (linked below) which mentions that a map $f:V:=GF(2^{m}) \rightarrow V$ which vanishes at 0 is APN if it satisfies the condition that it is a binary code $C_{f}$...
3
votes
1answer
48 views
What does 2-flat mean when discussing APN permutations?
I am currently reading a research paper that uses the term 2-flat. However, I don't understand what this term means.
For example, the paper mentions in its definition of APN that for all distinct $a$,...
-1
votes
2answers
83 views
Are all block and stream ciphers symmetric?
I'm trying to categorize my knowledge. Can I place block ciphers and stream ciphers under symmetric with RSA/DH under asymmetric?
4
votes
2answers
110 views
Generate one-time-pad with pre-shared key and public randomness
I know very little about cryptography, so I apologize if the question does not make sense.
Let's say we design a function $F(P, X) \rightarrow K$ that takes in a pre-shared private key $P$ and a ...
1
vote
1answer
68 views
How to compare one time pad security and efficiency with AES?
It seems that the minimal size of Pseudorandom permutation (PRP) output is $128$ bits. In general, I'd like to see if there's any minimal size of the output of pseudorandom function (PRF) as well? for ...
1
vote
1answer
80 views
Can POS devices really generate random numbers?
I am doing an implementation of a system designed by a payment company and I am a little skeptical about the way they have designed the end to end cryptography.
The system is as follows:
There are ...
1
vote
2answers
87 views
How many keys in a Hybrid Cryptosystem?
If symmetric cryptosystems have $C^2_n$ keys, and asymmetric systems have $2n$ keys, how many does a hybrid system have? This was in an online quiz from school
Company A is considering to adopt ...
1
vote
1answer
378 views
How Secure is gpg Command Using Symmetric AES-256 From Being Cracked
How secure is any data encrypted using the following command:
gpg -o *encrypted_output_file_name* --symmetric --cipher-algo AES256 *file_to_be_encrypted*
...
0
votes
0answers
72 views
Computing a probability
Let $(w_1,\cdots,w_l) \in (\{0,1\}^\lambda)^l$, and $r_1,\cdots,r_l $ are chosed as uniformly random from $Z^*_q$ such that $r_1+\cdots+r_l=0$ and $q$ is a large prime number. Also, Let $F$is a ...
2
votes
1answer
127 views
Explaining Chaotic Cryptography
I will venture myself into studying chaotic cryptography. However, I find it hard to explain what chaotic cryptography entails to those that have some knowledge of cryptography. Neither can I explain ...
0
votes
1answer
100 views
Format of hybrid crypto envelope structure?
From posts including the accepted answer to
How to encrypt file with RSA and AES that anyone with RSA key can decrypt them?
hybrid crypto (AKA envelope encryption) a GPG-encrypted file has an ...
0
votes
1answer
50 views
Send content to owner of gpg public key, nested content symmetric encryption
If I want to encrypt a text content file using a symmetric algorithm like AES,
is there a standard format gpg will expect, where it can detect a symmetric key (encrypted with recipient gpg public key ...
0
votes
1answer
56 views
PRGs exist if computationally secret encryption schemes exist
I have understood the "equivalences" between PRP, PRF and PRG. Now, I just read an statement in my lecture notes that made me think that there has to be a conversion between PRG and computationally ...
-3
votes
1answer
58 views
One-time pad question (Old ciphers) [closed]
The plaintext SECRETIVE is encrypted using One Time Pad with key DDDDDDDDD. Which of the following is TRUE?
The ciphertext will be the same as using Caesar cipher with key of 4
The ciphertext is the ...
3
votes
1answer
324 views
Security of AES after key expansion 4-MB with ECB and CBC
My question is,
how does the security depend or change if I encrypt with AES-128 in total 4-MB of Data?
With Electronic Code Book Mode and
Cipher Block Chaining Mode ?
Does an adversary still ...
2
votes
1answer
96 views
Detect MITM with hashed session-key — Is my protocol secure?
I have the following setup:
An app ("client") wants to communicate securely with a device I created ("server").
The client has the public key of the server (and a hashed password) preinstalled.
I use ...
1
vote
1answer
67 views
Can a message be encrypted with BOTH mono-alpha and poly-alpha ciphers?
For my class assignment, I was given this text;
Qpuvu vo vv stazpuykzh Hhycmlmv asb. Ad dhyaqva wh uyo uzb jpwww Avlw.
Tkpjllfdmbp zoatz vzjavfvna ZLHqh. Amva luy yyvlz yu bhk zua zlhvvalaz
yow ...
3
votes
1answer
73 views
Change a secret key in an embedded device
There is a device that uses a secret key Sk to encrypt data.
Assume this Sk is compromised.
Could the following scheme be considered safe, in case we want to change the compromised Sk:
We store some ...
6
votes
1answer
128 views
Combining classical attacks and quantum cryptanalysis
I'm regularly reading that AES-256 is secure against quantum computers because Grover's algorithm will only halve the key strength (i.e. "only" require $\sqrt{2^l} = 2^{l/2}$ operations instead of the ...
4
votes
3answers
406 views
In what cases might PRESENT be implemented as encryption-only?
In the paper, under section 4.1 Goals and environment of use we read:
In applications that demand the most efficient use of space, the block cipher will often only be implemented as encryption-only.
...
0
votes
1answer
53 views
Does repeated xoring of the (same) key K lower the entropy of K?
If a symmetric encryption key $K$ has been generated by some recommended (NIST for example) RBG then we should have a key with high entropy.
But if we xor other bit-strings (e.g. IVs, other keys, etc....
4
votes
0answers
109 views
Why are matrices so common in symmetric encryption?
Matrices have been used in symmetric ciphers since the Hill Cipher (before?) all the way up to modern ciphers such as Twofish and AES.
I understand matrices can be invertible, therefore making them ...
4
votes
0answers
74 views
Patent Status & Usability of AE Modes [closed]
Post Structure:
Sources Cited
Question & Details
Before You Answer
Useful Info From Comments
Sources Cited:
https://blog.cryptographyengineering.com/2012/05/19/how-to-choose-authenticated-...
1
vote
0answers
216 views
CPA-secure private-key encryption scheme that is unforgeable but is not CCA-secure
This is exercise with 4.26 in Katz and Lindell's introduction to cryptography 2nd ed.
The question is: Show a CPA-secure private-key encryption scheme that is unforgeable but is not CCA-secure.
...
2
votes
2answers
345 views
Is there a symmetric cipher that is explicitly designed to be slow?
I am trying to find a symmetric cipher that is explicitly designed to be slow. I realize that this is generally not desirable, but I'd like many cycles and lots of electronic action. I could modify ...
1
vote
3answers
127 views
Could ANY cipher serve as the foundation for a public key cryptosystem?
My reasoning goes like this:
In principle, any trapdoor function can serve as the foundation for
an asymmetric encryption scheme.
All ciphers are trapdoor functions, since it's easier to encrypt ...
0
votes
1answer
56 views
Hash ratchets with truncating hash function
I'm working on a forward secret messaging system that relies on hash ratchet. I'm using BLAKE2b as the one-way function, which by default produces 512-bit digests. These digests are truncated by my ...
2
votes
2answers
302 views
Decrypt Base64 Encoded Monoalphabetic Cipher
I'm attempting to decrypt a body of ciphertext which has been encrypted using a monoalphabetic cipher. The trouble I'm having is that the plaintext was base64 encoded before being encrypted. In this ...
0
votes
1answer
113 views
Oblivious Encryption: Oblivious Transfer Based Encryption
I’m aware of a couple of OT protocols, most of which use Public Key Cryptography, Key Establishment (or similar constructs) as the base. I don’t really have specific knowledge on other OT protocols, ...
5
votes
1answer
152 views
Why do block ciphers use key schedules instead of round constants? (Even-Mansour)
Let's take AES as an example. What would be wrong with just having a 256 bit key that you XOR into your input and then XOR into your output? No key expansion at all.
I believe it's even known as the ...
9
votes
0answers
201 views
What was the BassOmatic cipher, and what made it so weak?
According to Wikipedia, this homebrew cipher was originally used in PGP, before Phil Zimmermann replaced it with IDEA. Supposedly, insecurities in the algorithm were pointed out to him, leading to ...
