# All Questions

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### Usage of Fermat primes in RSA

Why are Fermat primes ($2^{2^n}+1$) useful as $e$ (the public key) in RSA encryption? I understand why $2^n+1$ primes are useful, because they would simply be ...
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### Does re-iterate AES128 with different keys gives any benefict?

I'm not cryptography expert (well, I'm here after all!) but I have this doubt… Suppose I have 2 different keys: secretkey1 secretkey2 And a plain text: myReallySecretPlainText If I use AES128 ...
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### How to specify last $t$ bits are only sent when a signature is sent?

I have read that in cases where there is a limit on the amount of data sent over the network, one idea is to sent only $t$ bits of data rather than sending all the bits. For example, in the Schnorr ...
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### Authentication and deniability

I have the following problem: Alice wants to send Bob a message such that Bob knows it is from Alice but at the same time he cannot prove that Alice send him this message. The solution I came up ...
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### What is the padding scheme for the original Tiger hash?

The specification doesn't seem to indicate how to pad messages to the requisite 512-bit boundary. What is the padding scheme for the original Tiger hash?
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### Is it feasible to break an encrypted and later encoded message?

A message is sent from a person to another. The plain message is first encrypted, even with a weak algorithm - say, DES. Then, the encrypted message is encoded with a simple substitution, which is ...
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### Secret sharing - no dealer, modifiable, verifiable

I need to find a secret sharing scheme with these properties: The scheme is set up by all participants, ie no single entity called the dealer The parameters of secret sharing need to be ...
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### Hardness of finding mutual discrete logarithms of small generators in $\mathbb{Z}_p$

Suppose you want to select a prime $p$ such that finding e.g. $log_2(3)$ in $\mathbb{Z}_p$ is expected to be either at least as hard as the general Discrete Logarithm Problem in $\mathbb{Z}_p$, or at ...
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### cryptography permutation [closed]

Let $\pi$ be a permutation of the integers $0$ through $2^n-1$ (the integers that can be represented in $n$ bits). For example, $\pi$ could be used as a substitution cipher in which each plaintext ...
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### One-way function and uninvertible function [closed]

How can I prove the following: If $f$ is a one-way function, then it is an uninvertible function?
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### Z*p Generator (Cyclic Group) in java

I am trying to implement ElGamal in java without using the in-built libraries. The problem occurs when I am trying to find the generators of the number(in this case 11). Everything works perfectly ...
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### ElGamal encryption with private key [closed]

Does the encryption with a private key and decryption with a public key works in ElGamal likewise what is done when we use RSA for sender authentication?
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### Avoiding overflow when encrypting with RSA

When encrypting with RSA one calculates $m^e \pmod n$ by doing the following: m^e % n Where $m$ is what we encrypt. Often $e$ is a very big number to make it ...
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### Generating bilinear pairing parameters - running time of finding member of p-torsion group

Update: Question completely rephrased. I want to create the parameters for a bilinear pairing (the Tate pairing in this case). In case you're interested I'm following this thesis, specifically the ...
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### Method to calculating e in RSA

For simplicity I choose two small primes for p and q. p=3 q=11 n=33 Φ(n)=20 Now we need ...
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### Why do we use 1024 / 160 bit primes in DSA?

I am looking at DSA's parameter generation and don't understand why for $p$ a 1024 bit prime is needed if $q$ is chosen as a $160$ bit prime. I thought that the security of DSA relates on the discrete ...
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### Predicting Java's PRNG using partial output

I have a program (a game) that uses Java's nextInt function with parameter 0x10000 to get a random 16-bit number. Java's ...
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### Would requiring reciprocal signatures create a stronger Web of Trust?

In this post on Cryptome it's noted that a person called Michael Vario is willy-nilly signing people's public key's and uploading those signatures. He is effectively forging a web of trust. I'm sure ...
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### Choice of reduction polynomial in Whirlpool's internal cipher

Whirlpool is an interesting little hash function in the Miyaguchi-Preneel family. In my mind, it's most interesting feature is the design of internal cipher W, where the distinction between key and ...
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### Cryptanalysis of an certain algorithm

Is an attacker of an cryptographic algorithm allowed to change order of sub-keys but not changing their number in attack? Would it be called an attack on broken algorithm of cipher?
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### How cryptographically secure was the original WW2 Enigma machine, from a modern viewpoint?

If cryptanalysts today were to crack the original Enigma machine, how fast/ how easily could they do it? What methods would they use? The original cracking was significantly helped by operator ...