# All Questions

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### Is a Mersenne-twister cryptographically secure if I truncate the output?

I want to create an online roulette game. Is it OK if the PRNG is seeded only once, when the user starts the game, or is it recommended to re-seed sometimes during game? Maybe just seeded once a day ...
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### RSA Encryption and Signature - Weak Padding

Assume that I have an plaintext $m$ and it is padded with $randompad||00||m$ and then it is encrypted with RSA and a public encryption key so we get the encrypted $Sm$. Then to assure its integrity ...
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### Select right SSL cipher suite for set top boxes (sh4)? [migrated]

We have lots of set top boxes with sh4/STb7109 CPUs, that feel quite sluggish when accessing HTTPS websites. I would like to find out which SSL cipher suites are most appropriate to use for our ...
40 views

### Is the following authentication protocol insecure?

I am a student taking cryptography this semester. I was just wondering why can't we use this simple protocol? Alice ----Open Connection--> Bob Alice <-- Cert$_b$--- Bob Alice --- ...
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### RSA Signature Weak Padding Attack

Assume that we have a message $m$ of size $n$, and it is padded with two 01 bytes in front. Then the signature $s$ is computed using a private key $ks$. Can we ...
81 views

### Private Messaging

Suppose Alice and Bob wants to send messages through Sue without revealing to Eve that the exchange took place. Slightly more formally, I don't want Eve to have any advantage telling if Alice is ...
93 views

### In S/MIME, are the same certificates always used to sign and encrypt messages?

My assumption is that S/MIME almost always utilizes certificates as follows: My certificate can be used to allow people to encrypt messages and send them to me. My certificate (the same ...
98 views

### Differential Cryptanalysis of FEAL-4

I'm currently carrying out a differential attack on the FEAL-4 algorithm, however I have hit a bit of a wall. Basically I attacked the final round first ($K3$) using the differential characteristic ...
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### What vulnerabilities would open up if PGP authentication didn't have integrity checking?

It is my understanding that PGP has both an integrity check and an authentication check. What vulnerabilities would open up if it didn't have that integrity check? It seems like the authentication ...
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### (1,k) Oblivious transfer [on hold]

The chooser generates a new key pair (x; pk) Gen(1n), a random number r R and sets c Epk(; r). He sends (pk; c) to the sender. For i 2 [1; k], the sender chooses random ri R, computes ci = ...
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### How to check the validity of one DES rotation?

I have written a python program to do one DES rotation. Is there is any program that enables me to check the validity of this code? PS: Permutation tables used are from pyDes. ...
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### Can I use the cipher text ouput of only one DES rotation as plaintext to check validity?

I have made a python code for one DES rotation. Can I use the resulting cipher text as a plain text for the same rotation with the same key? I think the answer is no, I can't do so. But I need to be ...
41 views

### Using Index Calculus against El Gamal? [duplicate]

Up to how many bits can IndexCalculus method handle when using it to solve a discrete log problem, specifically solving the private key of El Gamal encryption schema? I am dealing with 120-250 bits ...
37 views

### Unforgeability and type of adversary

When trying to prove security of asymmetric signature, for instance for existential (or strong) unforgeability against chosen messages attack, do we need to consider the signer as a possible ...
57 views

### What is the difference between CSPRNG and PRNG?

Is there performance differential between them? For example: we use PRNG for key generation which is very expensive and CSPRNG for IV/nonce in block ciphers which is fast? What is the difference ...
58 views

### Zero knowledge proof?

Alice is color blind. She never knows if her gloves are matched. Her brother Bob always teases her saying her gloves are mismatched and she should go change them. Alice wants to know if ...
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### Logical OR operation in a homomorphic additive cryptosystem

Suppose we have a cryptosystem homomorphic for addition (say Paillier's). Is there a way to perform a logical OR operation between two binary values (with a binary result). We can, of course, obtain ...
117 views

### RSA exhibits symmetrical properties

This question is broken into two sections really: Symmetry in RSA I have been analyzing raw RSA and I have noticed some interesting symmetrical properties of the algorithm. Assume that $M$ is a ...
67 views

### Multi-party encryption algorithm

To give some foreground information: I acknowledge that I am a cryptography newb and not by any means an expert (and probably never will be). In a recent CS class we had several assignments writing ...
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### What is the best (thoroughly covering) textbook for application of LFSRs in cryptography? [on hold]

What is the best (thoroughly covering) textbook for application of LFSRs in cryptography? (Beside Cipher Systems by Beker & Piper)
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### Type A Curves of Supersinglular

In the Type A curve used in Pairing based Cryptography, what is meant by sign0 & sign1 in the expression below? ...
58 views

### Is this the mathematical equation for the Vigenere Cipher

Is this the mathematical equation for the Vigenere Cipher or something else and if something else what is it? Where t is the letter of plain text and n is the position of t within the text and c is ...
44 views

### Why are the lower 3 bits of curve25519/ed25519 secret keys cleared during creation?

I am currently experimenting with ed25519 and I noticed that on secret key creation, bit 254 is always set and the lower 3 bits are always cleared. I found that bit 254 is always set to protect ...
16 views

### How to implement cramer-shoup algorithm in ios [migrated]

I want to implement cramer shoup algorithm in ios for asymetric cryptography... can i use crypto++ if yes then how to use that it is similar to cramer shoup algorithm... please give me soution...
86 views

### Merkle Tree High Tree

I'm reading Merkle tree signatures and I like know if the security of the that scheme depends, also, of the high of the tree or only depends that hash function is resistant to collision?
60 views

### Which data to share in CTR mode?

Suppose I've two clients A and B. Client A encrypt data in CTR (Counter) mode to get a ciphertext. What information will client B have to receive from A to decrypt the ciphertext? key, IV/nonce and ...
22 views

### A substitution cipher for two different alphabets? [on hold]

Is there a program out there (or a way to program my own version) that substitutes x for 1, b for 2, and can decode? I can use random symbols, but I need an 8 to 26 transversion. I could just use ...
149 views

### Can anyone give an example where (asymmetric) crypto can go wrong due to selection of wrong groups?

Basically the title says it all. It would be great if someone could tell give an example using provable security. More information about groups can be found at: ...
38 views

### Diffie-Helmann insecure on addition modulo n

Assume that G is the set Z$_{n}$ = {0 .. n-1} for a 1024 bit integer and + is addition modulo n. Then why would Diffie-Helmann key exchange in this group be insecure?
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### Elliptic Curve Verifiable Secret Sharing

I'm reading this paper, which on page 3(Section IV.C) presents a Jointly Random Verifiable Secret Sharing Scheme for Elliptic curves. The algorithm makes sense to me save for this part: "Each ...
129 views

### Would it be possible to create a game where one would need to decrypt a simple encryption?

This might sound pretty weird, but I was thinking of a game a person could play alone with a pen and paper. I got this idea where the person would write a random four letter string on a paper, and ...
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### What does this Authentication protocol achieve and what information is shared?

I am trying to learn everything I need to know for a Unit on 'Reliable and Secure Systems', but I'm struggling with the basics now. The question that I'm having trouble with is: "What is the ...
20 views

### Attacks against El Gamal private key [duplicate]

El Gamal encryption involves picking (p,g,b) which is our public key. We compute b=a^x mod p. Here, x is the private key which we don't know. What are some efficient and strong algorithms today used ...
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### Help with linear cryptanalysis

I am new to linear cryptanalysis, so I decided to try to break a toy cipher that was designed to be vulnerable to linear cryptanalysis. Unfortunately, I can't get it to work no matter how hard I try. ...
7k views

### How does asymmetric encryption work?

I've always been interested in encryption but I have never found a good explanation (beginners explanation) of how encryption with public key and decryption with private key works. How does it ...
248 views

### Implement deniable encryption with AES/RSA

I'm on a crypto app using OpenSSL (I'm more an implementer/cryptographer than a cryptologist), mainly as a hobby, for now. My app will be able to encrypt a file (not a container) with symmetric or ...
759 views

### What is “Implicit Authentication”?

What is “Implicit Authentication” in the context of authentication methods? I searched the Web but could not find any article that describes this. If anyone can describe it, that would be a great ...
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### Can someone Decrypt this for me? I cant figure it out [on hold]

my friend gave me this message and said it was for me, he made it using a code encryption thingy he made. I know for a fact that it IS a message and I really need to know what it says. I thought that ...
66 views

### What does pseudo pre-image of a hash function mean?

So finding a pre-image means given the hash value, one tries to find a message that gives this value using the function's standard IV. What about pseudo-preimage?