# All Questions

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I want to encrypt data and protect its integrity and confidentiality. However, I cannot increase the length of the data. Are there any cipher modes of operation which provide confidentiality and ...
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### Random numbers for Master Key and Key_block

Exploration through RFCs concludes that random numbers used in the creation of Master Key and Key Block(Key material for Encryption Key and Mac Secret) are from ServerHello.random and ...
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### encrypted file sharing protocol

I am trying to design a file exchange protocol for learning purposes, inspired by PGP, but fixing some of its shortcomings. Assuming the machine where the creation and decryption of the file happens ...
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### Should layered use of crypto always have a cryptographic binding between the layers?

Reading the latest TLS weakness, it seems that multiple weaknesses have been found over the years caused by not ensuring that messages are sent over the same channel, and in general a lack of ...
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### IND-CPA Security

Given a key $K$ (the key is fixed) and a nonce $N$ (changes from one message to another) Using a secure Key derivation function (KDF) such as the ANSI-X9.63-KDF with SHA-1 option to derive a key for ...
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### Determine the iteration times using Pollard's rho Method for factoring

Let's say, we have a large number $n=181937053$ and $f(x)=x^2+1$. And also we know that $n=12391 \times 14683$. The problem is that ,using Pollard rho method, can we find the algorithm iteration ...
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### Question on mono-alphabetic substitution cipher and poly-alphabetic substitution cipher

You know that a meaningful plaintext in a language with a 26-letter alphabet, like English, is encrypted using either the mono-alphabetic substitution cipher or the poly-alphabetic substitution cipher ...
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### Gallant-Lambert-Vanstone method

I am experimenting with the GLV method but cannot manage to get the right results according to the literature. I managed to find lambda, beta, split $K$ into $k_1$ and $k_2$ etc. for the curve I'm ...
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### What is the forward cipher function of AES-XTS?

We're using OpenSSLs EVP_aes_265_xts encryption on data (with unique, random, IVs for every new message encrypted) - which is working well. But, I've been asked; what is the forward cipher function ...
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### Decryption returns different data

I am new to cryptography so forgive me if I am doing anything stupid. I am following the Cryptography in JAVA book. I am creating my own kerberos. I am stuck at a point. I have Message class which ...
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### How can PBKDF2 be used to hash passphrases for ed25519 signing keys?

In trying to find a javascript implementation of ed25519, I came across this which says: The input must be 32 bytes long. As Brian Warner puts it, "Ed25519 keys start life as a 32-byte (256-bit) ...
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### Which gives better deterministic encryption SIV or Plain ECB mode?

Lets say , if we encrypt a plain text message $msg$ with key $key$ in below two ways. Which is the below would give better deterministic encryption and why ? AES-ECB($key$ , $msg$) SIV($key$, NIL , ...
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### How does converting character set affect hash entropy?

Does mapping a large character-set hash onto a small character-set hash lower entropy for a fixed size substring? I'm writing a python app that involves generating passwords for websites. During the ...
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### Known vulnerabilities in (EC-)KCDSA

Does anybody know if there's known vulnerabilities in KCDSA/EC-KCDSA? I have been researching for the past few hours and I haven't found anything. Wikipedia has very limited amount of information and ...
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### Plaintext patterns leaked based on single bit

Assuming that Elgamal is used as an encryption cipher, where lets say $p$ is 2048bit prime. Is it possible for an attacker to figure out $x$, a secret key, if any part of 2048 bits ciphertext and ...
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### What is the best way to verify a curve25519 identity?

A client identifies itself as a curve25519 public key. The server wants to verify the client owns the associated private key. What is the safest −and computationally efficient− way of doing so ? The ...
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### how to calculate power $n$ over Gaussian integers?

In the paper Extended RSA cryptosystem and digital signature schemes in the domain of Gaussian integers the authors calculate $(4007621+145835\cdot i)^{7848211742013} \mod (x)$, please explain to me ...
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### Key change and key derivation

there are two ways for key change: Key update and re-keying. Which of this methods use KDF (Key Derivation Function) for getting new keys.
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### Why do authors execute a leakage resilient election protocol inside a leak-free phase?

In the paper "Multiparty Computation Secure Against Continual Memory Leakage", on page 1241 (that's page 7 of the PDF) under section 2.3, the authors discuss "The Election Protocol" that they use to ...
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### Going Blind, Group or Ring?

I have several problems approaching the following problem: Let's assume that we have Alice, Bob and Cathy. Alice wants to present a message to Cathy, showing her that someone else has signed it (Bob), ...
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### non-abelian group based cryptography

I've read a lot about non-abelian group based cryptography recently and I am wondering why they only use infinite groups as platform. Is there a special reason or is this an area open for research?
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### DES encryption Algorithm

For DES, suppose that key k converts plaintext p into ciphertext c. If k’ represents the bitwise complement of the key k, p’ represents the bitwise complement of the plaintext p, and c’ represents ...
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### Question Error Correcting Codes

Let $C$ be a code over the finite field $GF(2)$ with generator matrix $G$ and parity matrix $H$. Let $e+C=C'$ be a coset of code $C$. Let $S$ be a non-singular matrix and $H'=H\times S$. Finally, let ...
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### inverse of scalar multiplier in ECC

I am learning to use ECC. i got into situation where i have $Q=abG$, where $G$ is the generator of the finite field formed on EC using a prime $p$ modulus and $a$ , $b$ are random numbers. now suppose ...
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### How to select parameters based on some condition

I am implementing a protocol for authentication where parameters need to be selected with $gcd(\mu,\phi)=1$ where $\phi=(p−1)(q−1)$. What is the best way to select the parameters while implementing
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### How does Bundle of CA Root Certificates work?

I followed the instructions found here: http://www.linuxfromscratch.org/blfs/view/svn/postlfs/cacerts.html To generate this file: ca-certificates.crt I am trying to understand which file I can use ...
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### measurable proof of works

We generally use hash functions as prof of work, for example we ask client to compute $x$ where $h(y|x)$ produce a sum starting with 64 successive zero bit. In cryptographic algorithms we can ...
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### Different between Shared Key and Common Key in DLP Application

What is the different between Shared Key and Common Key? Are they the same? Shared Key = Common Key?
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### So what is quantum cryptography anyway?

I am having difficulty understanding quantum cryptography concepts. I've searched the internet and watched some videos on youtube explaining the topic, but it is still hard to understand how it works. ...
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### Correlated or biased coin protocols?

There are a number of papers in the literature describing secure/fair coin flipping protocols. Unfortunately in my case, I am looking for coins that are epsilon-biased or epsilon-correlated. I am ...
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### If H(m) = 0 for some m, how can a DSA signature be forged?

If we know for some message $m$ that $H(m) = 0$, how can we forge a DSA signature with only the public key? I got that $g^s*r = (g^x)^r$ where $x$ is the private key, but that's one equation with 2 ...
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### Blum-Blum-Shub Cryptosystem

I am given $N$, which is Bob's encryption key. I was able to successfully factor $N$ into $N=p*q$. Alice encrypts a messages for bob and sends $a = [1,1,1,0,0,0,1,0,1,1,0,...]$ $b = 1545164156...$ ...
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### User's Privacy in certificateless cryptography

In practically, while doing registration with Key generation center in certificateless Signature,How can be a user do registration to the Key generation center without providing (Global ...
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### Can you clarify the proof that secure LR-two party protocols do not exist?

In the paper “Multiparty Computation Secure Against Continual Memory Leakage” on pg. 1237, the footnote #1 discuss why it is not possible to construct a leakage resilient two-party protocol. But I'm ...
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### Masking Parity Check Matrix Goppa

I like know: Is possible that any adversary PPT will be able to find the generator matrix $G$ of Goppa code $GC$, if given $SH$ matrix, where $H$ is a parity check matrix of $GC$ and $S$ is a random ...
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### Why does a joint leakage MPC protocol not directly apply to a disjoint leakage requirement?

In the paper "Multiparty Computation Secure Against Continual Memory Leakage" on pg. 1239 the footnote at the bottom points out the difference between $joint$ leakage and $disjoint$ leakage. The ...
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### Unblind a RSA blinded signature

I have blinded m = 16 with r= 13, e = 7 and n = 209. This resulted in m' = 464, which led to a s' = 8. Now, I want to unblind this s' by using s = s' * r$^{-1}$ but im stuck at filling in the ...
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### Example of CL PKC

I am trying to solve the example of algorithms of Certificateless Signature by manually and solving the mathematics of Algorithms but not succeed while doing mathematical calculations. Please ...
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### Replacing 8 sBoxes in DES with just 1 sBox, expected result?

Ok, i am trying to modify DES by my own way. There will be just one sBox and it will also contain all values from other 7 sBoxes. How it affects DES in this case? [? more secure/less ...
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### hybrid PKE scheme CCA2 insecurity

I'm reading a paper here say: As we know, in hybrid PKE schemes XOR alone cannot perfectly hide challenge bit to the CCA2 adversary The author does not define hybrid PKE schemes. What is ...
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### About private keys of certificateless cryptography

While reading Identity Based Cryptography and Certificateless Cryptography , Can any one tell why should private key generator(PKG) or Key generation center (KGC) generate private keys for users..? ...
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### How to Generate rsa keys using specific input numbers in openssl?

I am new to openssl so asking this question here for help. I selected 2 prime numbers p and q. Calculated public pair: (n,e) and private key: d. For ex. ...
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### Certificateless Signature

Consider the following scenario: There are two users: A and B. Users A and B generate a pair of their own public and private keys PUBa, PRIa and PUBb, PRIb. There is one trusted center(TC) that ...
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### What is the default type of salt for encryptions in Heimdal Kerberos?

I am trying to figure out what the salting mechanisms are for various kinds of encryptions in Heimdal Kerberos. In section "4.11 Encryption types and salting" of the Heimdal Kerberos documentation it ...
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### PGP encryption options

I recently began using PGP desktop and found several options for my encryption capabilities. Which of these (AES, Cast, Triple DES, TwoFish, IDEA) is the most recent, firstly, secondly may the NSA not ...
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### Is there any restriction in using lossless compression algorithms for huge key sizes?

I'm studying McEliece and Multivariate Public Key cryptographic systems. The main problem here is the huge key size. Is there any restriction in using lossless compression algorithms to fix this ...
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### Use of Different keys with PCBC

Currently I am having a doubt, while making a "DES PCBC" encryption on an image I observe a bit of the silhouette of the image (Probably because of the XOR between plaintext blocks and ciphertext ones ...
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### How many messages needs to be send to server to get AES key in Cache-timing Attack

I'm trying to evaluate the correlation between key length and the number of messages that needs to be send to server during Cache timing Attack. I read both D. Bernstein, “Cache-timing attacks on ...
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### How do multiple parties agree on a target block to hash for?

Bitcoin style blockchain… I have party(node) A, B, C and algorithm X. Algorithm X generates the first half of a target hash input - the "solution" to the problem. I want A, B and C to sign their ...