# All Questions

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### Image sharing without data overhead

The idea is to share n images among n persons so that all images can be reconstructed by someone in possession of all shares. However, there must not be any data overhead (which means the shares sent ...
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### If you hashed a hash an infinite number of times would you end up with a unique hash?

If you took a hashing algorithm for example MD5 and passed the output hash back into the algorithm an infinite number of times would you end up with one unique hash? My idea is that the maximum ...
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### How does ROTL work?

what does ROTL stand for? I know it does left shifting but what about the acronym? When we do a left shift, do we take the leftmost bit and add it at the end, by making the second bit the first, and ...
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### SHACAL-2 vs. AES as underlying block cipher for Secure Hash (aka SHA-256)

The hashing scheme SHA-256 (for instance) is based on Merkle-Damgard construction with the underlying compression function based on the block cipher SHACAL-2 configured in Davies Meyer mode. SHACAL-2 ...
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### Use of Lamport's Signature as a primitive

Is Lamport's One Time Signature used as a primitive to construct any other cryptographic protocols?
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### SHACAL in SHA-256

I was reading about hash functions, namely SHA, and I read that it is made of the Merkle-Damgard construction. And then the text said that the compression function used is based on the Davis-Meyer ...
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### S-Boxes and SP-Network

I work on an exercise and I have to study functions as : $f : \mathbb{F}_q \rightarrow \mathbb{F}_q$ with $q = 2^n$ which can define a S-Box for SP-Networks. There is a question that I can't answer ...
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### El Gamal Decryption with Big Numbers

I have a message decrypted in ElGamal. I was wanting help on how to decrypt it. Here is the data that I was given. p: ...
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### Non adjacent form of an integer is unique

I have tried to look up the proof for NAF (Non-adjacent form) being unique for every integer, but as far as I have seen, textbooks only mention it as a property of NAF, but no proof is given. Also I ...
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### Decoding Base64 encoded password with internal hashing [on hold]

I was given a username and encoded password list to decode. The list came from an export function of Cyberoam firewall (physical device), and was a .csv Username,Password,Email list. I expected the ...
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### can you solve exercise 1.20 Stinson [on hold]

Can you help me for solve exercise 1.20 of "Stinson" text book? Excuse me.I have no time to write the exercise.
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### Figure 2 in the Verifiable Computation - Pinocchio

I am reading the Pinocchio paper (verifiable computation): http://research.microsoft.com/pubs/180286/pinocchio.pdf The paper is rather hard for me. For the Figure 2, I guess $v_1(x)$ should be ...
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### Computation indistinguishability questions

The definition I have is: Two probability ensembles $X = \{X_n\}_{n \in \mathbf{N}}$ and $X = \{Y_n\}_{n \in \mathbf{N}}$ are computationally indistinguishable if for every probabilistic ...
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### RSA encrypted in logarithm. Is it right or wrong? [closed]

Factorization and primality test of Lepore-Santo in 4*log [(Y-X)/6]+1 I will show you the basic example, that i sto say the factorization of two prime numbers because reterating this process we can ...
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### Can a cryptographic hash be used as a cryptographic RNG?

Say I roll a six sided die 200 times (6^200 = ~2^517) and string all the results together into a long string of numbers and hash then result with SHA-512. Can I use that result for cryptographic ...
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### Asymmetric cipher with multiple public keys

Asymmetric cryptography is well known. You generate a private key. Using the private key you generate a public key. Then you can sign a message with the private key and check signatures using the ...
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### Is this transposition cipher information-theoretically secure for 1 message?

Given: $m = \{0,1\}^{n}$; a plaintext message of length $n$ encoded in binary $k = randomshuffle([0, 1, ..., 2n-1])$; A secret key consisting out of unique numbers between 0 and $2n-1$ in a true ...
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### Does SRP reduce to DH key echange when shared password is not secret?

I can find JavaScript implementations of SRP (Secure Remote Password protocol), but nothing that inspires confidence for Diffie-Hellmen key exchange. I also have a separate need for SRP later. I ...
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### Can you help me understand what a cryptographic “salt” is?

I'm a beginner to cryptography and looking to understand in very simple terms what a cryptographic "salt" is, when I might need to use it, and why I should or should not use it. Can anyone offer me a ...
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### RSA: Why must e be relative prime to phi(n) [duplicate]

I've got a question concerning fields used in RSA: Let's use the following symbols for my example: {p,q} = primes {e,n} = public key {d,n] = private key I learnt that an inverse element exists if a ...
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### How to securely map an element from an smaller domain to the other element in a large domain

Problem: I have a small sized domain, say s-bit. It's clear that the probability for an adversary to guess an element is $\frac{1}{2^s}$. I need to make the probability negligible. However, I need to ...
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### Has human-generated entropy ever been a real problem?

I know the topic of human brains generating random numbers has been discussed here and in Cognitive Sciences before, but I am interested in a particular part of it: In an introductory book to ...
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### Montgomery Reduction

I'm taking a hardware cryptography class and working on a problem that focuses on Montgomery Reduction. So by definition: Computing a x b (mod N) Pick R, s.t. R > N, gcd (R,N) = 1 Compute N^-1 ...