# All Questions

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### How is public key cryptography used for digital signature?

In public key cryptography, there are two different keys used for the encryption and decryption of data . I am wondering how it is used for digital signature
1k views

### Passing data securely through QR codes?

We have to implement a way to securely transfer data from a POS to a mobile app using QR codes. The mobile app gets the payment parameters (amount, description, purchase_id, store_id) to create the ...
225 views

### Private Information Retrieval and Writing at the same time possible?

Are there any (possibly multiserver) private information retrieval (PIR) schemes that support private reads and writes (so called PIR Writing) at the same time, while having sublinear (in the database ...
56 views

In may application, I have a series of real number $\{v_1, v_2, \ldots, v_N\}, v_i\in\mathbb{R}$. To protect them, I add a random noise $r\in\mathbb{R}$ to each themselves like one-time-pad encryption ...
355 views

### Is there any existing cipher capable of scaling from a 1 bit key up to a one-time-pad?

We have ciphers that handle small amounts of entropy, such as a 256 bit key for AES; and we have one time pads for enciphering 1:1 entropy, such as a 1GB key for a 1GB file if you could ever harvest ...
71 views

### What are some of the new directions of research in Elliptic Curve Cryptography?

I am searching for some new research areas in ECC for my masters' project. My professor suggested me to go for Image Encryption using ECC. But I am clueless as to what are the new directions possible ...
29 views

### Solve matrix products

This question follows-up from two old questions. Suppose, there are two $n\times n$ non-singular binary matrices $X$ and $Y$. The product $XY$ is given. I guess, we can agree it is not possible to ...
20 views

### Block slicing operation and side-channel attack

I got block slicing operation in my cipher. I mean after each round we take first $a$ bits and second $b$ bits of 128-bit block and then compute $b+a$. $a$ and $b=128-a$ is computed from key schedule ...
38 views

### Decomposition of Sbox in three shares x1,x2,x3?

ex: $x| 0|1|2|3|4|5|6|7|8|9|a|b|c|d|e|f|$ $s(x)| 1|a|4|c|6|f|3|9|2|d|b|7|5|0|8|6|$ now how to split $x$ such that $x=x_1+x_2+x_3$
48 views

### Why are RSA and ECDSA sign and verification time different?

I would like to know why ECDSA signs faster than how it verifies? On the other hand, why RSA verifies faster than how it signs?
48 views

### A known plaintext attack on Elgamal Cryptosystem where the random is fixed

Let the public key of Alice be $(p, g, h)$, where $p$ is a big prime $g$ is a generator for $\bmod p$ $h=g^a$. The secret key for Alice is $a$. Bob wants to communicate with Alice, so he encrypts ...
46 views

### Modifying the One-Time Pad so that one key can be used two times

I'm currently working on a modified one time pad and I'm trying to use the encryption scheme such that the key will be used twice. I have written a small pseudo code but I'm stuck. Here is my attempt: ...
55 views

### Padding requirements for a stream cipher

You are given a stream cipher and a block cipher with a block size of 64 bits. The data input is 32 bits. How many bits do you need to pad before processing the data input using a stream cipher?
130 views

### Asymmetric encryption that preserves the plaintext size

I'm looking for an asymmetric encryption algorithm that preserves the size of the thong in clear text. The encrypted file must not be longer than the plaintext file and must not contain any special ...
72 views

### Which is more secure, AES CTR or OTP with generate key?

My idea of the OTP is to generate from 50 letters (5 words, each 10 letters) a new pad of 2000 random letters, then attach user email to the pad end (to make it unique). The keywords and the pad will ...
52 views

### How to calculate base value in modular exponentiation

If you have $a^b \bmod n = c$, and $b,n,$ and $c$ values are given, is it possible to find a value for $a$ within a given range? So is it possible to find $a$ in $a^{2051} \bmod 3149=636$ knowing a ...
128 views

### Encryption algorithms that can be used for key exchange and can be eavesdropped

Which algorithms can be used for key exchange between two wireless nodes and are not secured, meaning they can be eavesdropped?
49 views

### Deterministic procedure for mapping an arbitrary value into a 𝑝,𝑞 pair for public key cryptography

I want public key cryptosystem to used for re-encryption as describe in Can Paillier ,RSA or any other schemes be used for universal re-encryption like elGamal? Now i have little solution for ...
908 views

### How to find the key of XOR encryption in Java?

I am trying to find the key of an XOR-encrypted string in Java. It is very probable that the key is eight characters long. I have the encrypted string. I do not understand how to go backwards and ...
41 views

### Rijndaelcipher mix column query

I quote a wikipedi para that says The operation consists in the modular multiplication of two four-term polynomials whose coefficients are elements of ${\displaystyle \operatorname {GF} (2^{8})}$. ...
302 views

### What is the difference between Forgery and Chosen-Message Attacks?

I did some researches about forgery attack and chosen-message attack. For me, forgery attacks are more focused on the verifiability whereas chosen-message attacks are similar to brute-force attacks. ...
101 views

### Original papers for hashing functions

I would like to learn how hashing functions are discovered / created. In part of this process I think it would be helpful to see the original works or papers of any authors of cryptographic or non-...
55 views

### Verification of the NI-ZK Proof

I'm currently learning about ZKP and Non-interactive zero knowledge (NI-ZK) but I'm confused in the process of NI-ZK verification. I have taken the following example to learn about NI-ZK from this ...
81 views

### Zero Knowledge Interactive Proof vs zero knowledge proof

What is the difference between Zero Knowledge Interactive Proof and zero knowledge proof? Nathan Aw
66 views

### why Blum-Micali algorithm is deterministic algorithm

Can anyone give me the answer of the following question. Justify why Blum-Micali algorithm is deterministic algorithm ?
105 views

### What algorithms to use for a secure transport protocol on devices with limited computing power

I am new to cryptography. My questions is this: I process packets on runtime. I do not have time for advanced encryption or decryption techniques that take a long time. As far as I know, going with ...
93 views

### XOR of users password Scrypt key and Random 32 bit salt?

I am trying to encrypt users private keys with the user password but if a user provides a weak password then the scrypt key generated from it will also be weak and suspectible to attack. Let say the ...
564 views

### Cube root modulo prime

I make research about big numbers in finite fields and I need to calculate a cube root modulo prime P for the number N: ...
136 views

### How can I protect AES-256 encrypted data?

In April 2017, Jacob Henning asked "What are the chances that AES-256 encryption is cracked?" and part of his question was how best the transmitted data, now in his web database, a.k.a. "data at rest" ...
145 views

### Encrypt 2 numbers preserving arithmetic correlation

I want to encrypt 2 numbers using a public key and have the reader know the correlation between those 2 numbers. I can also share the public key. Example: ...
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### Decide whether a polynomial is invertible mod $q$

When implementing NTRU related cryptosystem, I came across the problem of deciding whether a randomly generated polynomial is invertible mod $q$. How to solve it?
764 views

### Elliptic curve discrete logarithm problem and mini example

Consider the group E23(9,17), this the group defined by the equation y2 mod 23 = x3 + 9x + 17 mod 23. What is the discrete logarithm k of Q = (4,5) to the base P = (16,5)? the solution is: 2P = (20,...
181 views

### Rabin Encryption is not CCA secure

Why is Rabin Encryption is considered as not CCA secure and how can I prove it? Any example would be helpful.
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### What is the result of encryption if Feistel cipher maps every 16 bit input to 0xFFFF regardless of subkey?

Suppose the F function of a 16 round Feistel cipher mapped every 16-bit input R, regardless of the value of the subkey K[r], to 0xFFFF What is the result of running an encryption with this cipher?
179 views

### A quick way to justify whether $a^m \equiv 1 \pmod{n}$?

Say I would like to justify whether $10^{28} \equiv 1 \pmod{29}$. I know according to Fermat's little theorem that $a^{p-1} \equiv 1 \pmod{p}$ when $a$ is a primitive root modulo $p$. What about ...
616 views

### how to encrypt the chat message with multiple people public key together and restore the message?

I have a application with two users and one middle man, all of them holding the private and public key, To make the secured chat, two users and one middle man are all sending the public key and ...
249 views

### Random number generator in a 2p2 Network

for my thesis I am trying to develop a system where nodes from a peer to peer network agree in generate a random number every tot seconds. I am stocked in this problem since almost 1 week anyone can ...
241 views

### RSA public key verification based on a secret

I'm attempting to develop my messanging app with encryption evolved. For now I came up with algorithm for authorization and message exchange. P.S. conneciton between server and client is over https ...
96 views

### Question about key establishment protocol and key exchange attack

If an adversary $M$ observes a session of the protocol between $A$ and $B$ and learns the session key $k_{AB}$.How Can the adversary mount a successful impersonation attack and communicate with $B$ on ...
73 views

### Simple hexadecimal to 2s complement question

From 2.5.1 in this paper, how is $p$ = FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFE FFFFFFFF 00000000 00000000 FFFFFFFF = $2^{384} − 2^{128} − 2^{96} + 2^{32} − 1$ ...
200 views

### ECDH can be used for Key Agreement(KA) as per ECIES specification?

I want to implement a library to provide ECIES (Elliptical Curve Integrated Encryption Standard). We could see DH can be used as KA function for ECIES. I want to know specifically the ECDH (Elliptic ...
99 views

### Reversing key exchange algorithm

I'm analyzing some software and finding key exchanging procedure. Its looks like very similar with Diffie–Hellman, but not the same. I can’t understand the purpose of this. The step of algorithm is: ...
943 views

### RSA : if my key and message are too large , how to do?

I want to send a message consisting of a string of number (e.g: 124124134235235) Then, p:125243 q:56454547 e: 2659043 d: 5261378624675 However, it will be too large...so, is there any solution to ...
410 views

### GMW Protocol with semi honest adversaries

I know the GMW Protocol is secure in the case of a semi honest adversary which control all the parties except one. However I want to proof that it is also secure in the case the semi honest adversary ...
128 views

### Classical cryptographic key exchange

I am currently reviewing for my exam and a questions comes to my mind when I read an example about a simple key exchange protocol. In my textbook, the author comes up with an example about a simple ...
101 views

### Finding greatest integer m satisfying modular relation

I solved (c). I want to know (a) and (b) For (a), what i have done is that p-1=t2^s(t is odd) = 2^s (mod 2^m) And for m=1,2,...s, both sides are 0. So, m is s or more than s. For m= s+1, s+2,... what ...
3k views

### How to generate sha 256 hash using https url

I want to generate sha256 hash of https url. ex: url "https://www.google.com/" I want sha hash of this url. I have tried extracting public key from ssl certificate and used following command. ...
99 views

### Table of Curve Paramters

I'm studying Elliptic Cruve Cryptograhpy. When I do a search on Google of ECC, I find some pdf where I see these curve's paramters: $q, h, r, exp1, exp2$. What are these parameters ? Are there tables (...