3
votes
3answers
101 views

In an A5/1 stream cipher, why do the registers have a stepping probability of 3/4

I know that the probability of each register to step is 3/4 but I have yet to find an explanation of why. Can anyone explain this to me?
1
vote
0answers
71 views

How to calculate min entropy of the output of PRNG?

As min entropy of a random variable provides the maximum probability of getting the desired realization of the random variable, which is the most conservative way of measuring the uncertainty of ...
1
vote
1answer
40 views

What is the last value in a cipher suite?

I understand that a cipher suite should contain the MAC algorithm at the end. So ECDHE-RSA-AES128-SHA256 should use SHA256 in HMAC for the MAC. But what about the ...
1
vote
1answer
90 views

Encrypting a string as smaller pieces vs. encrypting it as a whole

Is there any difference between these two ways to encrypt a string using FPE? Say the string has the format is specified by this rule First part is in the set $S = \{\text{AA,AB,AC,BA,BB,BC,CA,CB,CC}...
3
votes
1answer
49 views

Bitwise operation question with shifting involved

I am trying to find a value of X (32 bits) such that ((X XOR a)+b)<<3 = (X+c) XOR d. <<3 means shift left 3 bits. a,b,c and d are all constants which have been determined elsewhere. ...
1
vote
3answers
139 views

List of post quantum cryptography protocols [closed]

What are the post quantum cryptography protocols that have been proposed until now? I know about McEliece cryptosystem, and LWE scheme. What are the others? Can you provide me a list or a website ...
1
vote
2answers
125 views

Best non-digital cipher?

Is there an undisputed cipher that was considered the best before the computer age? (This is not suppose to be a discussion, it's either a yes or no.) Please give a brief description why it is yes ...
1
vote
1answer
80 views

Determine whether a given function is a pseudorandom generator/function

I am trying to solve the following three tasks (for exam practice, not as a homework): Define $𝐺 : \{0,1\}^* \rightarrow \{0,1\}^*$ by $G(x_1,...,x_n) = 𝑥_1 \oplus 𝑥_2,𝑥_1,⋅⋅⋅,x_n.$ Prove that ...
1
vote
1answer
42 views

Monoalphabetic cipher using different languages in the same plaintext

Today I learned the principle of the monoalphabetic cipher. It's simple to decrypt a ciphertext written all in the same language (english for example) because I can use the syntactic properties as ...
0
votes
2answers
46 views

How to find element g order q, given 2 large primes p and q where q|p-1

i have calculated 2 large primes, $p$ (minimum 2048 bits) and $q$ (minimum 224 bits), where $p-1 \mod q = 0$ by using SageMath. $p = $...
1
vote
2answers
83 views

Decrypt affine cipher given encryption key [duplicate]

i have a ciphertext C=TLNJG formed using the equation c=(7p+11) mod 27,c equivalent to numerical equivalent character of ciphertext and p the plaintext how do i ...
2
votes
0answers
54 views

Prove that the given scheme is CPA secure or not

Given: F is a length preserving PRP. Encryption scheme $\Pi$ for messages of n/2 bits where: $m\in\{0,1\}^{n/2}$ $k\in\{0,1\}^n$ Enc: Select a random string $r\in\{0,1\}^{n/2}$ and output $c\...
1
vote
1answer
39 views

Composite vs Prime Order Groups in Attribute Based Encryption

Reading about Accountability in ABE currently and the paper "White-box traceable ciphertext-policy attribute-based encryption supporting flexible attributes" when comparing its system with an existing ...
1
vote
2answers
52 views

Merkle signature scheme

I was browsing the Wikipedia article on Merkle signature schemes and noted that it says: The number of possible messages must be a power of two[…] Why is that? ...
1
vote
0answers
63 views

A topic for my master thesis on post quantum cryptography [closed]

I am a master´s student. I am interested to work on post quantum cryptography. None of my professors are offering any topic this year related to post quantum cryptography. However I have the freedom ...
1
vote
0answers
45 views

Rijndael variant using AES for key schedule?

The weakest part of Rijndael is considered to be the key schedule (I believe that this is true for all variants, including ones not standardized as AES). One solution to this problem is to use (...
1
vote
2answers
49 views

Tell where messages begin and end in a series of ciphertext blocks?

With block ciphers, I understand that the plaintext is first broken down into the right-sized blocks, padded, and then encrypted into the same number of cipher blocks. Once these blocks are sent over ...
3
votes
2answers
59 views

Non primitive lfsr sequence

Given a non-primitive LFSR sequence (i.e number of states is less than $2^n - 1$); how do we find out the the characteristic polynomial? Will Berlekamp-Massey algorithm work in this case? for example;...
6
votes
1answer
163 views

Is there any benefit to verifying PKCS#7 padding when using AES CBC and HMAC?

As I'm using HMAC to ensure integrity and authenticity of the ciphertext, is there any additional security benefit to verifying PKCS#7 padding when decrypting using AES CBC? A previous question asked ...
3
votes
1answer
54 views

Is rubberhose cryptanalysis a sidechannel - formally?

I recently was engaged in a discussion in Sec.SE where somebody used the term "sidechannel" to actually mean "circumvent the encryption". By what he said it was clear, that he wanted to not bother ...
2
votes
1answer
60 views

Why is $Mac_k(m_1||m_2) = ⟨F_k(m_1), F_k(m_1 \oplus \overline{m_2})⟩$ not a secure MAC?

I am preparing for an exam and trying to solve the following question I found on the internet: Let $F_k$ be a pseudorandom function. Show that the following MAC for messages of length $2n$ is ...
4
votes
2answers
148 views

Help with breaking AES reduced to 2 rounds

I was studying Rijndael AES proposal, and its cryptanalysis. I started with writing code to break AES reduced to 2 rounds. I am using 128 bit key size and 128 bit block size. 2 round AES means the ...
1
vote
1answer
53 views

How to compute the discrete logarithm of Diffie-Hellman with a composite modulus?

Imagine $n = pq$ with $p-1 = 2 p_1 p_2$ and $q-1 = 2 q_1 q_2$. I can compute the discrete logarithm of $y = g^x \pmod{n}$ by computing the discrete logarithm of $y$ modulo $p$ and $q$. But then how ...
3
votes
0answers
22 views

Can GCM auth be bitsliced?

Is it possible to use bitslicing for GCM? This seems like a way to allow for a way to avoid cache-timing attacks without PCLMUL instructions and with good performance.
7
votes
4answers
202 views

Why haven't we proven many things computationally secure yet?

Brute Force is infeasible for just about every algorithm we use today. Yet, attacks are feasible. This is because weaknesses keep coming up in our algorithms. Why? We have proven lower bounds for ...
-2
votes
1answer
65 views

How to XOR two hex values and am I doing crib dragging correctly? (OTP)

Let's say I have the two cipher texts 7ECC555AB95BF6EC605E5F22B772D2B34FF4636340D32FABC29B 73CB4855BE44F6EC60594C2BB47997B60EEE303049CD3CABC29B According to this website http://xor.pw/? the result ...
3
votes
1answer
75 views

Why is this homomorphic encryption correct?

In LTV-FHE, section 3.3.2 Formal description, a ciphertext looks like this $c=hs+2e+b = (2g/f)s+2e+b$, where $h = 2g/f$ is the public key, $f$ is the secret key, $g, s$ and $e$ are chosen randomly, ...
3
votes
1answer
109 views

Why is not there any ideal S-Box?

i read about linear cryptanalysis and about S-Box that there is not any ideal S-Box (ideal S-Box is a random S-Box in another words S-Box that bias of input and output bits is zero) then i read about ...
0
votes
0answers
15 views

Why Sflash signature scheme is constructed in this way?

Sflash is a Multivariate signature scheme that was accepted by NESSIE in 2003, and completely broken in 2007 by a differential attack. Despite I know the total break of Sflash signature scheme and the ...
1
vote
1answer
31 views

Secret key agreement by public discussion from common information

There is a paper: U. M. Maurer, Secret key agreement by public discussion from common information, IEEE Trans. Inf. Theory, 39(3) 733-742 of 1993, with an IMHO fairly impressive title but having ...
1
vote
0answers
17 views

For the LTV-FHE scheme, after how many additions should modulus switching be used?

From the LTV-FHE paper I find out that after every multiplication there must be a modulus switch to mitigate the noise in the resulting ciphertext, besides relinearization. But, assuming the ...
1
vote
1answer
91 views

What is the importance of 1 < d < φ(n) and 0 ≤ m < n in RSA?

I'm a first year Maths undergraduate and we have recently gone onto RSA. I understand the majority of the algorithm using Fermat's Theorem etc. From the algorithm stated on Wikipedia: 4) Choose ...
1
vote
1answer
82 views

“Security” of SHA functions (Wikipedia), what does it mean?

Wikepedia's table Comparison of SHA functions mentions "Security(bits)" for some SHA functions. From the ratio (Output size (bits): Security(bits)), I feel it is something like "collision resistance". ...
1
vote
1answer
73 views

How to encrypt and decrypt a transposition cipher?

I encrypted the text hello there with a 3x4 table with the key 2 1 3. I fill in the text into the table row by row and got the ...
1
vote
2answers
86 views

Levels of strength: The Caesar Cipher

SITREP: I am deciding what form of "Random" Number generation would fit best for a Caesar Cipher that encrypts each letter with a different integer as a shift. This encryption is being handled via C# ...
1
vote
1answer
55 views

Number of shifts in DES key schedule

In DES key schedule some rounds use one left shift while others use two left shifts. What is the reason behind this?
1
vote
0answers
34 views

Partially homomorphic addition - not all parties present

I often see homomorphic encryption as a solution to a problem where a server wants to know the sum of $n$ users' numbers but can not know each individual users' number plaintexts. My question is: if ...
0
votes
0answers
20 views

Is there any difference between a one-time pad and a Vigenère cipher with a long key? [duplicate]

I've been browsing Wikipedia and stumbled on the article for the Vigenère cipher. I realized after seeing the example that it's quite similar to the one time pad, except with a short key repeated as ...
1
vote
0answers
24 views

Can we use the sponge construct to efficiently authenticate any cipher?

The sponge construct facilitates authenticated encryption independently of the function used to mix its state. Could we use any strong cipher (i.e. AES-256) as the mixing function in a sponge to ...
0
votes
2answers
45 views

Trying to understand MixColumns with Hexadecimal matrix

I am trying to read and understand the textbook's exercise questions. The sample solution at the end the textbook has a final answer and it does not clarify how it got the result. I am trying to ...
4
votes
0answers
52 views

How does Boneh–Lynn–Shacham work?

As described by Wikipedia, BLS uses Diffie-Hellman in some way. I understand how Diffie-Hellman works in both its normal and elliptic curve forms. But what is the "pairing function"?
4
votes
2answers
106 views

Distribution of hash values

I was wondering if the uniform distribution of hash values is a generally required criteria for cryptographic hash functions. The english wikipedia article only mentions four main properties. But it ...
4
votes
1answer
52 views

How is McEliece chosen plaintext secure?

Suppose a challenger creates a McEliece encryption system where there is a public key consisting of a matrix $G$ representing some linear code, and a number $t$ for the number of errors. Then the ...
0
votes
0answers
22 views

Confidentiality then Integrity with different keys [duplicate]

Can anyone describe how we can do what is said in the below sentence which is in Mark Stamp crypto slides (PPTX) on slide number 101 : Can do a little better - about 1.5 “encryptions” The whole ...
1
vote
0answers
73 views

Confidentiality then Integrity with different keys

Can anyone describe how we can do what is said in the below sentence which is in Mark Stamp crypto slides (PPTX) on slide number 101 : Can do a little better - about 1.5 “encryptions” The whole ...
1
vote
0answers
45 views
0
votes
2answers
237 views
4
votes
1answer
167 views

great discovery in the field of elliptic curves cryptography?

Prof. Adi Shamir says in The Cryptographers' Panel 2016: i think that NSA has made a great discovery in the field of elliptic curves cryptography and NSA wants to avoid the increased use and ...
0
votes
0answers
11 views

Calculating inverse of transposition key cipher [duplicate]

I need some help on transposition cryptography. If I'm given the encoding key to a transposition cipher, how do I get the decoding key for it? I tried googling but couldn't find any steps on the ...
0
votes
3answers
48 views

Getting inverse of a transposition key

I'm new to security stuff and I have some questions about the keys of transposition cryptography. If I'm given the encoding key to a transposition cipher, how do I get the decoding key for it? I ...

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