# All Questions

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### Engima machine decoding with PC and GPU

I saw this answer at this site about decoding a 3-rotor Engima machine's settings: How cryptographically secure was the original WW2 Enigma machine, from a modern viewpoint? And did some math for ...
191 views

### How hard to break a cipher if it has a different key for each word?

Recently I watched the movie 'The Prestige' again but this time the cipher diary impressed me very well. I like to create my own cipher for my diary because I have some time to kill everyday after ...
672 views

### Strong key generation using PBKDF

I know that PBKDF2 is very useful for generating strong keys. I'm trying to know is there any additional contribution of the given password to produce even stronger keys. Which key is more secure: ...
235 views

### Does NTRU provide Perfect Forward Secrecy?

Does NTRU provide Perfect Forward Secrecy if the world would use it in an HTTPS connection?
236 views

### Last Round in DES

I am studying DES for my Cryptoexam .As far as I understood , the initial plaintext is permuted and then the left half is called L0 and Right half is called R0. After that for each round the process ...
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### Are there cryptographic hash functions with homomorphic properties? [duplicate]

Are there cryptographic hash functions that have homomorphism-like properties? E.g. satisfying following relation $h(a || b) = h(a) · h(b)$, where $h(x)$ is hash function itself, $x || y$ is ...
131 views

### Trapdoors for lattices

I refer to an article https://eprint.iacr.org/2011/501. I focus on (a bit modified) Algorithm 1 which runs as follows (in my understanding): For given $n, m\in \mathbb N$, $q=2^k$ and a distribution ...
207 views

### Equal length of primes in paillier cryptosystem

In the key generation step of paillier cryptosystem , In order to satisfy $\gcd(pq,(p-1)(q-1))=1$ , we can take equal length primes. Instead of taking(length as parameter to generate $p,q$) equal ...
239 views

### How often do I need to rotate AES 256 keys

I'm trying to design a protocol for a resource constrained environment. The device has to communicate with a server through an insecure node. My plan is to use AES 256 end to end for all ...
458 views

### Which block cipher mode(s) is most appropriate in these applications?

I have a few questions I'm stuck on for a cryptography course I'm doing, any help would be much appreciated. The first application is for decryption on a multicore processor. I assume any of ECB, ...
221 views

### Quantum key exchange skepticism/confusion

I was hoping somebody could explain some issues I have with quantum key exchange that I don't quite understand. I've read bits and pieces about BB84 but I'm sure my questions probably apply to other ...
278 views

### How can I map arbitrary group elements to unique integers without using Hash functions?

Let's say, I have a group $G$ of large prime order $p$. A set $S$ consists of $n$ random elements chosen from $G$. Without using a collision resistant hash function $H$, how can I map elements of $G$ ...
737 views

### Isn't a simple Vernam cipher as secure as known symmetric key algorithms?

I have just read little about the Vernam cipher and the problems of implementing it. But, in practice, would not the key, if generated by a commonly used programming language's ...
4k views

### Can I remove new lines in a public key?

Can I remove new lines from the rsa public key file to get a one line string? So the question is if the key looks like this AAA BBB CCC or ...
976 views

### SHA512withRSA - Looking for details about the Signature Algorithm

I am trying to find information about the Signature Algorithm SHA512withRSA and have been unsuccessful so far. In the current state, the signature is too long, so I would like to check the code for ...
1k views

### breaking fully homomorphic encryption schemes

Fully homomorphic encryption schemes allow one to evaluate any arbitrary computation over encrypted data. Intuitively this seems to be too weak, irrespective of how we achieve this. An adversary who ...
109 views

### Privacy-Preserving Protocols and Proofs of Security

While dabbling in privacy-preserving protocols (mainly using Semi-Homomorphic Encryption) and coming up with miscellaneous ideas for comparison tests or other similar primitives, based on obfuscation ...
108 views

### Does the initial exchange of random tokens in SKID3 authentication assure against replay attacks?

As the question suggests, I wanted to get a sanity-check on this issue... is it the case that the use of a random token exchange during SKID3 authentication itself constitute a prevention of a replay ...
150 views

### Why verify padding at all?

Whenever a ciphertext is decrypted using a block-cypher, we need to remove the padding. There are different ways to add padding, but they usually set the last byte of the last block to the number of ...
230 views

### Are there valid attacks on full SHA-1?

Google today announced they are sunsetting SHA-1. Its fine by me. But that made me realize I am not keeping up with the research on SHA-1. The Wikipedia page only says Stevens' attack is the most ...
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### How do you create a large PRP from a small one?

How can you efficiently create a pseudorandom permutation with a large domain given a PRP with a small domain? Meaning: given an $n$-bit PRP, how can I create an $n k$-bit PRP? I'm only interested in ...
128 views

### Generating S boxes that satisfy Coppersmith's criteria?

I'd like to generate all possible 6-bit to 4-bit S-Boxes that satisfy the criteria for S-Box design given by Coppersmith, but I have a few doubts: How many such S-Boxes are possible? Is there any ...
256 views

### “Practical” operations supported by functional encryption?

I'm curious about what operations have been developed into functional encryption schemes. What I mean by that is: what operations can be performed over encrypted ciphertexts? Obviously homomorphic ...
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### What does $\to$ mean in the following definition of a block cipher?

In the following picture $\kappa$ is the key length and $n$ is the block size. I understand that $\{0,1\}^\kappa$ means all possible combination of keys and $\{0,1\}^n$ means all possible combination ...
420 views

### DES S-Box properties

Two of the properties that lead to the design of DES S-Boxes are: 1)For any non-zero 6-bit difference between inputs, no more than 8 of the 32 pairs of inputs exhibiting that difference may result ...
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Padding oracle attacks are a huge nuisance when using CBC mode encryption without authentication. Wouldn't all those padding oracle attacks be avoided if we'd just use bit padding instead? Or is does ...
303 views

### How to prove Security of Onion Layers of encryption?

CryptDB has Onion layers of Encryption to provide wider functionality from weaker forms of encryption. How do we prove such things are indeed secure ? Intuitively It seems ok. Are there any parallels ...
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### Why does FIPS 186-4 require specific sizes for keys?

In FIPS 186-4, page 32, about FFC crypto it is required that the length of $p$ will be exactly 1024 bit and the length of $q$ will be exactly 160 bit. Why is the requirement not stated in terms of ...