Mathematics Stack Exchange
Mathematics Stack Exchange

Questions tagged [cryptography]

Questions on the mathematics behind cryptography, cryptanalysis, encryption and decryption, and the making and breaking of codes and ciphers.

Please only post questions about the mathematics of cryptography here.

  • Coding and implementation specific questions should go to Stackoverflow with encryption or cryptography tags.
  • You may also consider asking at Cryptography Stack Exchange which is for asking questions about the mathematics and properties of cryptographic systems, their analysis ("cryptanalysis") and subsidiary topics that generally make up cryptology.
1915 questions
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Knapsack Decryption Help

I am currently trying to decrypt this superincreasing Knapsack cipher. I thought I understood how to do it, but the answers I am getting don't seem correct. Superincreasing w: [2, 9, 16, 43, 71, 156, 301, 619] q: 1337 modular inverse of r:…
Mayo
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ElGamal clarification

I'm just looking for a bit of clarification on a question I've found on ElGamal: You want to let people send you messages using ElGamal. You begin by choosing $p =101, g =2$ and $a =12.$ (a) Calculate your public key and then decrypt Bob's…
Lauren Burke
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Swap the encryption function with the decryption function

For any given one-key cipher (M,C,K,Ek,Dk), we may modify it into (M,C,K,Dk,Ek). In other words, we swap the encryption function with the decryption in the modified cipher. Prove that the two ciphers have the same level of security with respect to…
Ng Clement
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What kind of Encryption to use?

Is there any technique that could secure a public document from being counterfeited, given the constraint that the documents shall be available to cracker and hence an unlimited number of ciphertext and plaintext pairs shall be available to cracker…
Soham
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Affine Cipher finding the decryption map

Given two letters of the plaintext 'ZP' corresponding to the ciphertext 'AE' respectively, I have found the key to be (a,b)=(10,10) (modulo 26). Therefore the decryption map $D(x)=a^{-1}(x-a)\bmod26$ I obtain here is $D(x)=10^{-1}(x-10) \bmod26$.…
DavinaGoodman
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Number Theory Exercise, defining a set

Let N = pq be a product of two distinct primes. Show that if N and an integer d, where d is defined as : 3d = 1 mod ($\phi(N)$) then it is possible to compute p and q in polynomial time in the equation : $p^2$ + p(($\phi(N) - 1) - N) + N =…
user3317647
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How can I decrypt the ciphertext?

In RSA, how do I calculate $c^d \bmod n$ to decrypt a ciphertext $c$? Suppose that: $$ n= 120781\\ e=3\\ d=90043\\ c=38191 $$ How can I work this out by hand or with a basic calculator so that I can see the steps?
Jaja 1
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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 explanation?
user33984
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Meaning of the term "deterministic" in visual cryptography

In the paper " Random Grid and Deterministic Visual Cryptography with Enhanced color patterns" http://dl.acm.org/citation.cfm?id=2743130; uses the term deterministic. Can anyone help me to understand the significance of the term deterministic.…
user356595
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dining metaphysicians

I thought I'd read about this problem years ago, but cannot find the answer online. There is a more well-known dining philosophers problem that is vaguely similar. https://en.wikipedia.org/wiki/Dining_philosophers Here is my problem: three…
maibaita
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Understanding simple equality

Looks like I got stucked. Could you please help me to understand that simple equality? If $A\in\mathbb{N}$ and $B\in\mathbb{N}$ than why do we have $$ (7^B \pmod{11})^A \pmod{11} = (7^A \pmod{11})^B \pmod{11} ? $$
AseN
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RSA Cryptography, finding the secret key

Alice, Bob and Eve are all present in the classroom. Alice and Bob want to agree on a password that Eve will not be able to know. Eve has access to all communication between Alice and Bob, and Alice and Bob share no common information unknown to…
TheRapture87
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ECB mode decryption

I have used the ECB mode (with block length $4$) to encrypt the message $m=1011000101001010$ into $c=0010011001001101$ using the key $$\pi = \begin{pmatrix}1&2&3&4\\2&3&4&1\end{pmatrix}$$ and initialisation vector $IV=1010$. Now I to decrypt it we…
user2850514
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RSA Paper Example

I am reading the 1978 paper on RSA Algorithm. There is an example included in the paper and there is a section I can't get my head around. It says: Since $e = 10001$ in binary, the first block ($M = 920$) is enciphered: $M^{17} = (((((1)^2·…
Alice
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$RSA$ cryptosystem with $e=2$

There exists a $RSA$ cryptosystem with $e=2$ , where $e$ is the encryption exponent ?(In general $e>2$)
ale
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