# All Questions

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### Does Linear Cramer-Shoup have pseudo-random ciphertexts?

"Linear Cramer-Shoup" is defined on pages 4 and 5 of $\:$ eprint.iacr.org/2007/074.pdf . Are the ciphertexts in Linear Cramer-Shoup computationally indistinguishable from uniform under a ...
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### How do you construct a practical full-domain hash function?

I am looking for practical constructions for Full Domain Hash. I have read Random Oracles are Practical by M. Bellare and P. Rogaway, the construction suggested on page 8, under "Uniformity: a ...
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### Using chi square for distinguishing between compressed and random data

I am trying to find some measurement for identifying and distinguishing between compressed and random data. I tried this first by computing the entropy of such data, the entropy value is extremely ...
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### Length of data to hash for PGP

I have finally managed to verify some simple PGP signed message blocks. However, I discovered that for some reason, my implementation limits me to verifying data that is 9-16 bytes long. no less. no ...
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### Comparison: complexity measures vs. security

Assume that you want to compare several cryptographic primitives (say, encryption schemes), and choose one. You need to consider several complexity measures, such as the key length, encryption time, ...
905 views

### Can you help me understand the Common Modulus Attack in a Lucas Group?

I'm trying to decrypt a message that is encrypted using a LUC encryption scheme and running into roadblocks. I know that with RSA if Alice and Bob use the same public modulus but different encryption ...
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### An Elliptic curve cryptography implementation which can be terminated

I'd like to have an implementation of elliptic curve cryptography along the lines of secp256k1 which is secure until some information is published after which it is broken. One idea would be to use ...
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### Is a changing public truecrypt container secure?

I have a Truecrypt container which I want to synchronise between computers (i.e. different people, that I want to share the data with). If I used Dropbox for synchronisation and someone downloaded ...
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### Better lower bound on min-entropy

In “Randomness Condensers for Efficiently Samplable, Seed-Dependent Sources” by Dodis, Ristenpart, and Vadhan (PDF), I have seen the statement that: any tuple of distributions $(X,Z)$ is $ε$-close ...
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### Elligator-2 against curves over Fq, q mod 4 = 3

It appears that the conditions for applicability of Elligator-2 against many of the SaveCurves curves, where $q \mod 4 = 3$ will inevitably poke a hole in the bit-string set over $(0, 1, .. (q-1)/2)$. ...
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### Quantum computing vs AES s-box equation

Do quantum computers have any affect on the ability to solve the non-linear AES s-box algebraic expression, or does solving it still fall under search algorithms (Grover's)? If quantum computer do ...
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### Missing public exponent

Using LUC RSA, I have a list of 8 public keys $(R_1,n_1)$ through $(R_8,n_8)$, and a list of $8$ messages $M_1\dots M_8$. The messages have all been double encrypted. However, one of the public key ...
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### Is the reverse of the “discrete logarithm problem” equally dificult? [duplicate]

It is not easy to understand why this becomes a hard problem. The discrete logarithm problem as defined here: “any integer k that solves $b^k = \{g\mod{n}\}$ is termed a discrete logarithm” i.e.: ...
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### Under what conditions did a Bletchley bombe stop?

I am trying to understand the conditions necessary for one of the Bletchley Park bombes to stop. Let me give an example. I have been experimenting with Enigma machine and bombe simulators to try to ...
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### Looking for C++/Python Open Source code library for cryptanalysis of classical ciphers [closed]

I've done a significant amount of coding over the years working on classical ciphers (e.g., Chaocipher, D'Agapeyeff). My main programming languages today are C++ and Python, although there was a time ...
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### Anonymisation resilient to key leak

Problem statement Elbonian citizens have been issued a card holding a random $B_j\in\{0,1\}^b$, $0\le j<2^n$, $b\ge n+20$ (representative example $b=64$, $n=28$). The habit has grown to use this ...
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### What are the current limitations (and capabilities) of Functional Encryption used for access control?

I'm trying to make my way in Functional Encryption used for access control. I read a lot of papers such as "How to Run Turing Machines on Encrypted Data", "Functional Encryption: New Perspectives and ...
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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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### Homogenous and heterogeneous Unbalanced Feistel Networks

Unbalanced Feistel networks can be homogenous (F-function identical in each round), or they can be heterogeneous (F-function not always identical in each round). The advantage of heterogeneous UFNs ...
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### understanding the proof of knowledge

Recently I've been reading the paper “A New Family of Implicitly Authenticated Diffie-Hellman Protocols”. It's very hard for me to go further. Especially when it comes to the proof of knowledge. ...
171 views

### Security of this deterministic encryption scheme

I recently came across a library that promises to do deterministic encryption with the following scheme: AES with 256 bit key in CBC mode with PKCS7 padding and Synthetic Initialization vector ...
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### Can a commutative block cipher be indistinguishable from a random one, assuming a random permutation of keyspace?

Define a commutative block cipher with keyspace the finite set $K$, and message space the finite set $S$, to be an application \begin{align} E:K\times S&\mapsto S\\ (k,x)&\mapsto ...
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### How has the “power” of cryptography evolved from its beginnings till today? [closed]

I'm looking for a historical overview for the change in cryptographic power, which I hereby define as How far state-of-the-art cryptography is ahead of state-of-the-art cryptanalysis. In other ...
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### What informal indicators exist for estimating the computational infeasibility of cryptographic problems?

When assuming a block cipher primitive is secure, or a number theoretic problem is hard, this assumption is usually based on how far we are from breaking the primitive or solving the problem using ...
284 views

### Is there a “brainwallet” for GPG keys? [closed]

“Brainwallet” is a program that takes a passphrase (hopefully a good one) and deterministically creates a Bitcoin wallet. This wallet can be used for transactions, then deleted from the computer. To ...
To formulate this question precisely, I will define an idealized hypothetical "perfect" hash function $H(n)$ which has nice scalability properties, and will formulate a problem PERFECT HASHCASH in ...