Tagged Questions
0
votes
1answer
77 views
If sent the same message m to Alice and Bob, how someone who follow the channel can find m ?
Alice has public key (n,ea) and Bob has public key (n,eb) with gcd(ea,eb)=1. If sent the same message m to Alice and Bob, how someone who follow the channel can find m ?
0
votes
2answers
168 views
RSA: Prove that all messages encrypt to itself
RSA: Prove that all messages encrypt to itself if $p=5$, $q=17$, $e=33$.
0
votes
1answer
147 views
RSA: What message will Alice receive?
In RSA, Alice chooses $p=47$, $q=57$, public key ($n=2679$, $e=11$). When Bob sends the message $m=3$, what is the message that Alice will read?
0
votes
0answers
44 views
How would I create a birthday attack? (Hash Functions)
I'm trying to create an birthday attack, but I can't seem to get through it as I've never done it before. The basis: We have $E_K$, an encryption function, which has $N$ possible keys $K$, $N$ ...
4
votes
1answer
97 views
RSA Encryption with number theory
I have a number theory class but my professor just put the homework about RSA encryption where we have absolutely no clue how to do, here's the two question, help appreciated:
a) A word has been ...
1
vote
0answers
157 views
Diffie-Hellman key exchange public key calculation
I encountered a question that I can't seem to get around it. Lets say user A and B uses the DHKE defined over $GF(2^8)$ induced by the irreducible polynomial $x^8 + x^4 + x^3 + x^2 + 1$ and the ...
1
vote
1answer
123 views
Expected number of tosses - coin tossing
I have here 2 methods for generating a random number, and I need to calculate the expected number of tosses for each method.
In each, we let n = log(N) Ne be the bit-length of N and let ...
1
vote
1answer
146 views
question on how to decrypt the message
A message is encrypted using an affine cryptosystem in which plaintext
uses the 26 letters A through Z (all blanks are omitted), the letters are
identified with the residue classes of integers (mod ...
1
vote
1answer
122 views
doing an attack on elgamal using pycrypto, how do i solve for this random K? [closed]
I am working on a cryptography homework, doing an elgamal attack. I am using pycrypto's package.
$(a, b) = encrypt(plaintext, K)$
where
$a = g^K \bmod p$
$b = (M * (y^k \bmod p)) \bmod p$
note* ...
0
votes
0answers
139 views
homomorphic encryption
Homomorphic encryption is a form of encryption where a specific algebraic operation performed on the plaintext is equivalent to another (possibly different) algebraic operation performed on the ...
0
votes
1answer
128 views
Diagramatic Puzzle
This is the Puzzle:
and this is the hint:
and the answer seems to be 000111 but I have absolutely no idea how it is done. Can anyonw help me out here?
That's the puzzle. There are no other ...
0
votes
1answer
58 views
Cryptographic Coding
If the word “BRIGHT” is coded as” OCPLKV”, then how will you code the word “SERIAL”?
1) CDKYFG
3) CKDGFY
2) FPYNDN
4)FPNDYN
5) none of these
Can someone give me the answer with a little ...
3
votes
3answers
103 views
3
votes
1answer
162 views
RSA public key cryptosystem
I got stuck on a homework question. If anyone could help me with this certain problem, I would be grateful. I'll state what the problem say and some relevant theorem (i believe) that I used to partly ...
2
votes
1answer
209 views
Perfect square modulo $n = pq$
I've been stuck on this problem for a while. Any insights to the problem would be great!
We start with $n = pq$, where $p, q$ are distinct odd primes. In addition, $\gcd(a,n) =1$. If $x^2 \equiv a ...
1
vote
1answer
127 views
RSA cryptography Algebra
This is a homework problem I am trying to do.
I have done part 2i) as well as 2ii) and know how to do the rest. I am stuck on 2iii) and 2vii).
I truly dont know 2vii because it could be some special ...
0
votes
0answers
59 views
entropy of perfect cryptosystems
I am working on the product of two perfect crypto-systems and I need to prove that the product is secure.
$$a -- [\text{system}\ 1] -- b -- [\text{system}\ 2] -- c$$
How can I prove that $H(a) = ...
2
votes
2answers
129 views
block cipher algorithm
Consider a block cipher algorithm with the properties:
- Input, output block length is 64 bits and key size is 56 bits.
- Given a key K, the key scheduling requires 2 microseconds.
- After the key ...
0
votes
1answer
178 views
AES Key Scheduler
How do you get the rcon for AES's key scheduler? Where does it come from; is it a constant because it seems to differ?
7
votes
1answer
1k views
Cracking Playfair code
I need to crack a Playfair encoded text without knowing the keyword. While searching the internet I found a way to do this using a 'shotgun climbing hill' method. Problem is, I can't decide how to ...
1
vote
1answer
244 views
Breaking RSA in a special case
This is a part of homework assignment, and I am stuck.
The RSA signature is being calculated using Chinese Remainder theorem technique. Find the detailed description here.
Public and private keys are ...
3
votes
1answer
211 views
How is the Schnorr Signature insecure in the following 2 scenarios:
When there is no hash function used, $s = k-x \cdot m \mod {q}$ instead of $s = k-x \cdot H(m||r) \mod{q}$?
When a hash function is defined as $H(m)$ instead of $H(m||r)$?
Ref: Schnorr Signature
2
votes
2answers
266 views
Why is hash function $h$ ($h(w_1 \oplus w_2) = h(w_1) \oplus h(w_2)$) not good?
Suppose $h$ is a hash function, $h$ : { 0, 1 } * $\rightarrow$ { 0, 1 } n and for all $w_1$, $w_2$ it holds: $h(w_1 \oplus w_2) =
h(w_1) \oplus h(w_2)$.
$\oplus$ is the XOR operation.
Why isn't $h$ ...
