# All Questions

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### How to construct Hash function of type H:{0,1} * X G -> Zp*?

In many cryptographic protocols design, I have seen the statement 'Choose a Hash function H1:{0,1}* X G -> Zp*' i.e a hash function which takes as input a binary string of finite length and a random ...
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### Hash function with iteration and concatenation

If a hash function H is collision resistant, are the following two hash functions collision resistant or not? (|| is concatenation) H'(m) = H(H(m)) || H(m) H''(m) = H(m) || H(m) My first approach ...
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### Is it safer to use timestamp in REST authentication?

I am working on a personal project to build a REST authentication system which authenticate clients via three parameters: ...
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### Why is AES-128 considered secure while RSA needs a 1024-bit size to be considered secure [duplicate]

I got asked this question today and I didn't know the answer, AES-128 is considered secure, the key size is 2^128, so you would need in average 2^127 tries to break the key. Why does RSA need at least ...
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### Do most TLS 1.2 implementations express curves in a canonical form when performing EC arithmetic?

Sorry if this is a silly question, but does anyone know if the cryptographic libraries which implement TLS 1.2 for Firefox, Chrome, etc. express a given curve in a canonical form (i.e. one of ...
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### Questions about a SHA3 cipher stream encryption scheme

I've written an encryption implementation using a hash as a cipherstream FOR DEMONSTRATION PURPOSES. I know it is slower than more sensible options such as AES but I'm interested in several things, ...
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### I have a challenge for anyone willing

I am incredibly new to the world of cryptography, and perhaps this isn't quite the best site to post on, but I was hoping I could gain insight from some smart minds on my method. I encrypted an ...
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### Possible to generate a one time secret which all nodes on the distributed network can know but cannot pre compute

I have a distributed P2P network. Everyday, I want each node to have a secret which is only valid for that day, while each of the other remaining nodes on the network will be able to calculate the ...
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### Extracting key bits from linear cryptanalysis equation for SDES

From the linear cryptanalysis of SDES, we get a linear equation consisting the K[1, 3] of the round key 1 and 2. From this how will I retrieve the key bit? How do we solve the linear equation we get ...
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### Vulnerabilities in specifying the hash algorithm used for signature verification on a per-message basis

Let's say that I have a 4096-bit RSA key and when I sign data, I typically use SHA-512. As far as I understand it, the hash algorithm used to sign/verify a message is specified in the message. If a ...
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### How are the attributes of a user authenticated in attribute-based encryption?

It seems that the papers I am reading do not talk much about this point. That is how the attributes of a user are authenticated in ABE system. To my understanding, there is an attribute authority ...
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### How is the root certificate transmitted to pc?

i understand that the purpose of root certificates and CA's is to ensure that the communication parties are who they say they are. But how is the root certificate acquired? Is it not possible that ...
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### Convert one encryption scheme to another without decryption

I want to convert one encryption scheme to another without decrypting the first scheme and then encrypting with the second scheme. For example convert OPE encryption to Paillier without decryption. ...
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### How can we define division operation by using Fully homomorphic encryption

Last fews months, I'm working with homomorphic encryption. Now I am dealing with some computational problems with integers or real-numbers (like arithmetic mean, standard deviation) where division is ...
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### How Diffie-Hellman authentication works?

There are a lot of good videos on a simple Diffie-Hellman in the internet but unfortunately that is susceptible to the MITM attack. I understand how with DH the two parties are able to calculate a ...
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### Caculated time One Point Multiplication with double and method

I am using double and add method for point multiplication in affine coordinates. How we compute 1PM in double and method? Di Wang said one point multiplication consists of repeated addition and ...
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### Gaussian distribution in lattices

In many lattice based cryptosystems, Gaussian distribution is used. Can you explain why only Gaussian distribution is preferred?
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### What does the probability subscript mean in Shannon's secrecy definition?

Shannon's secrecy can be defined as: $$P_M (M=m) = P_{SK,M}(M=m|E(SK,m)=c)$$ What does $P_M$ means? (same question for $P_{SK,M}$) I know that is the probability space M, M being the messages; I do ...
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### What happens to NORX if the same (key, nonce, header data) triple is reused

As I understand it, reusing a (key, nonce, header data) triple in NORX leaks the XOR of the initial common prefix (but this is zero, so only its length is leaked) the XOR of the first distinct ...
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### Fast hash for 64-bit inputs

I am looking for a fast hash (~few machine instructions) to be used for hash tables with 64-bit keys. I can't use SipHash as the hash function will be inlined in too many places and so the code size ...
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### How to design a deliberately weak PRNG for experimentation?

I'm looking for a PRNG that is deliberately weak, that is, follows a set of rules stochasticly. For example: Encounters a set of bits that is a multiple of X, starts exhibiting bias, or starts to ...
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### Dieharder text file for output of AES_CTR

I want to run Dieharder test suite on the output of AES_CTR. How should I form the text file consisting of the cipher text obtained from AES_CTR, to be run directly with Dieharder package for linux?
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### RSA private key finding method

Bob uses RSA with $p=83$ and $q=103$. His public key is $e=445$. Alice claims that she can calculate Bob's private key without using the definition $d=e^{−1}\bmod φ(n)$? But how?
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### why OCB over AES for authentication encryption?

why should anyone use OCB-offset code book over AES algorithm?
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### Determining collision resistance of a function?

I am having trouble trying to understand if the function is collision resistant. As I understand it, preimage resistance means that it is hard for an adversary to find two messages that produce the ...
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### Attribute based access control and role based, online bookstore example

I am asked to answer a question that says: One online book-store wants to grand access to clients regarding their subscription. There are 3 types of subscriptions A , B and C. Customers get access ...
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### Multi Authority Attribute Based Encryption Library

Anyone aware of a library that has MA-ABE implemented in any language preferably python? P/S - I hope this is the right place to ask this. Apologies if not, then a redirect will be appreciated
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### The sign of the correlation in linear approximation

${\text{Let }}g:{\{ 0,1\} ^n} \to {\{ 0,1\} ^n}$ be a round function of an $n$-bit iterated block cipher and let $K \in {\{ 0,1\} ^n}$ be a fixed round-key, and denote ${g_K}(x) = g(x \oplus K).$ Show ...
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### Have ciphertext and key but need to figure out encryption method

So I have a block cipher (I think) that I need to break. I have the ciphertext and the key, but not the method of encryption, and was wondering if anyone could help me figure that out? The key is a 9 ...
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### AES Twofish Serpent

AES-Twofish-Serpent how to create this combo encryption? I am using Linux Mint and i want to encrypt few big folders in one folder, but to be hiden.
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### M3 Bitlocker Recovery

Has anyone used this software? Is this a legitiamate solution? I am working on rolling out bitlocker encryption on some devices and I want to have a data recovery plan in place. I am looking for ...
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### What kind of obfuscation is used in this image? [on hold]

Edit: This is not off topic since I am not requesting analyzing or deciphering a block of data here. I'm NOT asking anyone to solve this, I'm looking for the name of the obfuscation technique used ...
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### OpenSSL & TLS1.2 with aes-cbc and initialization vector

I'm trying to manually decrypt DTLS traffic using OpenSSL and TLS 1.2. The cipher suite im using is AES256-SHA256 as listed here. Im able to decrypt the packets with the key that the server and the ...
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### How is a message digest decrypted?

Trying to get my head around digital signatures and hit a slight block. The book I am using gives the following information Device A hashes a message to create a message digest Device A encrypts ...
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### What are the pre-requisites I need to be able to code Salsa20 in C#?

I've taken a basic course in Cryptography and we've learnt various algorithms and their usage. I've implemented RC4 and Triple DES in C# with ASP.NET. For a project that I am a part of, I need to ...
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### Ciphertext with uneven letter distribution

I have a ciphertext encrypted with an unknown method. It is part of a challenge (personal quest), so I can not post it. The letter statistics is the following: ...
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### How big window is secure and practical with TOTP? [migrated]

We are using Time-based One-time Password Algorithm (Google Authenticator) in our system. Since we currently don't allow any time window and code validity is just 30 seconds, we are constantly having ...
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### Is reusing keys for CBC and CBC-MAC secure when using encrypt-then-MAC?

I know reusing keys is a bad idea, especially for CBC and CBC-MAC, but the example for why on Wikipedia seemed to use encrypt-and-MAC. It seems obvious that the last block of encryption will be equal ...
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### Linear cryptanalysis complete key guessing

In linear crypt analysis, partial sub keys are guessed and verified for its correctness with the help of plaintext and ciphertext. From the partial sub key, how it is possible to guess the complete ...
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### What is the time requirement for pairing computation and modular exponentiation?

I want to design a cryptographic protocol for encrypted search without pairing. I have seen some papers for protocols without pairing. How would I compare pairing computation and modular operations?
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### Why does a fixed key not make MACs like CBC-MAC or GMAC into secure hash functions?

Why does setting the secret key to a fixed, public value not make MACs like CBC-MAC or EMAC into secure unkeyed cryptographic hash functions? In other words, why is the resulting hash function not ...
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Can any one help me decrypt this message: noohaiisee spyg iOyh h ol ceet pbcuoonnss
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### How do you apply bilinear mapping to attribute based encryption?

I'm new to both bilinear mapping and ABE. I have a vague idea of how bilinear mapping works now, but I don't understand how it applies to ABE. Can someone give me an example?
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### Breaking Vigenere via Kasiski/Babbage method? (non-programmatic)

I'm really hoping someone can explain to me what is going on in the second major component of this form of analysis. If you wish, for convenience, here's a page that already has some ciphered text ...
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### Need CryptDeriveKey AES implementation in C#

I am integrating with 3rd party software that uses AES 128 encryption. I know this is not ideal, but the choice of encryption is up to the 3rd party software. I am using C#. My problem is in deriving ...
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### Permuted Hash Table

Suppose we have a hash table, $HT$, consisting of $100$ bins.The hash table uses a hash function $H$ that is public. We all know that given value $a$ we can compute the address in the hash by ...
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### Interesting Topics for Projects?

I hope this is not a off-topic question for the site, but I was wondering if I could get any recommendations for project topics in cryptography suitable for someone just learning basic material now. ...
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### How to create Crypto based Project

I took Cryptography course last semester and It was very interesting. To have a more practical understanding, I thought I should create a mini project. Below is the ...