# All Questions

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### How to construct a next bit predictor from a distinguisher

I read the claim, without proof, that it is possible to construct a next bit predictor for any PRNG given an oracle distinguisher for that PRNG and vice versa. How do I prove that? A distinguisher ...
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### pairing-based schemes

some authors claimed that computational performance of a pairing-fee scheme (based on scalar multiplication over an elliptic curve group) is about 1000% more efficient than a pairing based one I would ...
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### Clarification of the terms “brute force” and “guess”

In the answer to the question “What exactly is a negligible (and non-negligible) function?” There is a part in the explanation that – as far as my knowledge goes – is conflicting: But instead of ...
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### Does CCA security imply authenticated encryption?

Does CCA security imply authenticated encryption?
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### How does recovering the public key from an ECDSA signature work?

It is possible to recover the public key from an ECDSA signature (R,S). Please explain me how this works.
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### Effective security of block cipher – equal the key size, or half the key size?

The Wikipedia “Key Size” article states: The security of an algorithm cannot exceed its key length (since any algorithm can be cracked by brute force), but it can be smaller. … … … Most ...
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### Is jacobian to projective conversion unique?

I am doing a small project in ECC. I have used the following equation for converting Projective to Jacobian coordinates: $$D = AC\\ E = BC^{2}\\ F = C$$ and also the following equation to convert ...
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### Is there any _true_ anonymous cryptocurrencies? [migrated]

I've been looking into Bitcoin recently and stumbled upon numerous notes how Bitcoin is not anonymous at all, or how it's only partially anonymous and you can easily trace your funds. So, this ...
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### If I add a stream of true and pseudo random numbers, do I get another stream of true random numbers? [duplicate]

I am thinking of buying a USB hardware advertised as producing a stream of 'high quality' random numbers which I take to mean they are indistinguishable from a stream of 'true' random numbers. If I ...
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### Determining if a stream of bits is statistically random [duplicate]

Suppose I would like to build a hardware RNG. The details aren't important but let's say I've found a way to generate theoretically random bits, and I want to test to see if they are in fact "random ...
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### In RSA, why does $p$ have to be bigger than $q$ where $n=p \times q$?

In openSSL – during RSA key generation – if $q$ is bigger than $p$, they exchange them. Why is that?
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### Generate Finite Field power of g

consider the field $\mathbb{F}_{2^4}$, defined by using polynomial representation with the irreducible polynomial $f(x) = x^4 + x + 1$. Given element $g = (0010)$ as a generator for the field, How ...
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### CBC-MAC length extension attack with IV simulation

I'm doing Matasano's challenges and struggling with second part of 49th problem where I'm asked to do the length extension attack with CBC-MAC without IV manipulation. There is a hint that I can ...
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### What curve and key length to use in ECDSA with BouncyCastle

I'm developing a client/server system in Java which is not interacting with third party software, so I don't have to worry about compatibility. At a certain point, I need the client and server to ...
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### Use ElGamal to solve Diffie-Hellman problem

Say we are able to decrypt a Elgamal ciphertext $c$ using only the public key. Apparantly it is now possible to solve the Diffie-Hellman problem (given $g^a, g^b$ calculate $g^{ab}$). How? I know how ...
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### In symmetric searchable encryption are the algorithms public?

If a user (other than the data owner) possesses the secret key in symmetric searchable encryption scheme are they able to run the trapdoor algorithm, or is this not publicly available?
120 views

### Getting 88bytes cipher output from 48bytes input in AES

The other day I saw this Hybrid Cryptographic Algorithm in the Google and felt curious about it. I am trying to understand this Hybrid Algorithm. And hopefully its not so hard to understand whats ...
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### Cryptool - DES (ECB and CBC ) - double encyption

So, I uploaded a text file in Cryptool and encrypted it with DES-ECB with the key FF FF FF FF FF FF FF FF. I encrypted the cipher text again, with DES-CBC using ...
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### AES256-GCM - can someone explain how to use it securely (ruby)

I am looking into using AES256-GCM for encrypting some database fields. I know that for AES256-CBC, I need to generate a new IV for each encrypt, but I can use the same key. The IV can be openly ...
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### Is SipHash cryptographically secure?

I'm evaluating different hash algorithms for use in my application. One of the kind of algorithms I am looking at are cryptographically secure ones to protect against DOS attacks. SipHash seems ...
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### SHA256 output to 0-99 number range?

Is it mathematically possible to take a SHA256 hash and turn it into a 0-99 number where each number in 0-99 range is equally likely to be picked? As a 256 bit hash means the highest value possible ...
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### Public and Private key encryption in simple math

Can anybody show me (or point me to resource) how to generate public key and private key with simple math? Steps which can be reproduced in a simple calculator – so the message, keys all can be ...
127 views

### Algorithm for computing square roots in $GF(2^n)$

Short question: is there an algorithm for efficiently computing square roots in $\mathbb{F}_{2^n}$?
The Feistel cipher algorithm produces a pseudorandom permutation with domain size equal to $2^{2m}$ (for some $m \in \mathbb{Z}^+$). That is, a one-to-one function $\pi$ of the set \$\{0, 1, 2, \dots, ...