# All Questions

0answers
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### Showing that a function satisfies the properties to be a distance function

Let $p$ be a prime and $V_p$ be the associated valulation. Then for all $x,y,z \in\mathbb Z$, $V_p$ satisfies: $v_p(xy) = v_p(x)+v_p(y)$ $v_p(x+y) ≥ min(v_p(x),v_p(y))$ Define a function ...
0answers
8 views

### Negative exponents in Shoup's threshold RSA?

I'm trying to implement threshold RSA operations, starting with decryption based on Peeters, R., Nikova, S., & Preneel, B. (2008). Practical RSA Threshold Decryption for Things That Think. ...
1answer
66 views

### Why is factoring $p-1$ easy when $p$ is a safe prime?

A paper states: [...] $(p,g,y)$ is a correct ElGamal public key if $g^x=y\pmod p$. To verify this the order of $g$, and thus the factorization of $p-1$, is needed. This is easy for safe primes ...
0answers
8 views

### Problem in Entropy ?Please help me solve this [on hold]

Let the message space and cipher space be given by M= C ={00; 01; 10; 11} and the key space K = {k0; k1; k2; k3}. We denote M= {m0;m1;m2;m3} and the probability distribution of message variable M ...
0answers
6 views

### Can anyone explain about Correlation and Auto correlation attacks with easy examples? [on hold]

I find examples like 1) Find the correlation and auto correlation of a and b. and b has some data in it.
1answer
14 views

### With wrong IV at receiver side, the CFB in better than OFB?

Assume the receiver have a wrong IV (initialization vector), in the CFB mode only the first block of plaintext is wrong but in OFB mode the second and all blocks will be affected. Is that correct? ...
0answers
10 views

### Problem in understanding Blakley's Secret Sharing Scheme

I need to implement Blakley's Secret Sharing Scheme. I have read below mentioned two research papers but still unable to understand how to implement it. Safeguarding cryptographic keys Two Matrices ...
1answer
23 views

### Why isn't CTR mode (counter mode) used more often?

For the CTR mode, the design is good for parallelization, yes, it seems the benchmark of the program downloaded from crypto++ proves that on an Intel I7 CPU. My question is that as most of CPU on ...
1answer
42 views

### TLS 1.2 Handshake: How is the ECDHE public key signed by server?

I am dealing with a situation where a cipher option, such as ECDHE-ECDSA-AES128-SHA, is chosen for establishing a TLS connection. In this case, a server, when sending the ServerKeyExchange message to ...
1answer
106 views

### Does Ed25519 support cryptographic threshold signatures?

This is a loaded question so I'll list the concerns, not all of which need to be satisfied. Does there exist a threshold-signature scheme for Ed25519 that... Does not require a trusted dealer to ...
0answers
4 views

### binary vector in matlab [on hold]

please i need help in some problems in matlab .. 1- i need to create vector with binary number randomly . 2- i need to input numbers to algorithm and these numbers are binary . 3- i have " The ...
0answers
17 views

### How are the AES inverse S-Boxes calculated?

I would like to know, how to calculate the inverse S-box. I followed this link (with affine transformation first, then multiplicative inverse), but the result is wrong. For example, if I use the value ...
1answer
56 views

### Proving that an encryption scheme is susceptible to certain attacks

I'm currently trying to prove the following: Where p is a prime number of cryptographic size, prove that: e(m) = am + b (mod p) where a and b are private is open to a known plaintext attack e(m) = ...
0answers
11 views

### Hardness assumptions on composite order bilinear groups

I am not at all knowledgeable in elliptic curve cryptography. So, here lies a couple of questions that I failed to find answers for to my satisfaction. Is there any known Type-III bilinear pairing ...
0answers
21 views

### Is signing a message just encrypting it with private key? [duplicate]

I have a simple question, When I sign a message does the program encrypt the text with my private key? Because I can decrypt it with my public key. Yes or no. Is signing a message just encrypting ...
1answer
38 views

### Is there a strong cryptographic reason for GCM's 2^39 - 256 bit limit?

In reading through the original GCM specification (McGrew & Viega '05), the composition of the 128 bit Initialization Vector as a concatenation of a 96b nonce and a 32b unsigned wrapping counter ...
1answer
57 views

### Why can't you just clone encrypted data and use it?

Let's take a contactless card for example (one for public transport lets say (i.e. MiCard)), the data is encrypted on the card and encrypted on the reader as far as I know. So how come somebody who ...
2answers
63 views

### Reusing one-time-pad with random plaintext

I understand that by definition one-time-pad keys cannot be reused but I was thinking about the case where it is used to send random data and couldn't find anything on the subject so here is my idea: ...
1answer
38 views

### In ECC, how do I prove that point addition is commutative?

I am studying elliptic curve cryptography and this question is related to the commutative property of point addition operation. Point addition $P_3(x_3,y_3)$ of two points $P_1(x_1, y_1)$ and ...
1answer
41 views

### Diffie-Hellman on infinite groups

The most common groups to be used as examples for the DH protocol are modular multiplication and elliptic curves. But I've realised that the groups doesn't need to be finite, a suitable infinite group ...
0answers
16 views

### How to verify pgp digital signature + generic cipher question

When receiving emails, I sometimes see the following: -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 I found an integer overflow in PHP, in the conversation of dates to "Julian Day Count" ...
1answer
168 views

### Rock-paper-scissors over network, how to protect from cheating server?

I'm trying to design cryptographic protocol to play Rock-Paper-Scissors with two parties, neither trusting each other, nor trusting server they use for communication, so game is 'provably fair'. So ...
3answers
205 views

### Random Galois fields

Note: I have now answered this by my own research and can generate random fields up to G(2^9) in reasonable time. I would need to find more speedups for larger fields. At this time G(2^8) takes a few ...
2answers
56 views

### Books on cryptography mathematics [on hold]

I am currently reading the Book Understanding Cryptography from Cristof Paar. I am enjoying the book but i don't like to scratch the surface when it comes to cryptography. I would like do dig a little ...
0answers
53 views

### Scrambling sensor data [on hold]

I want to build a device that would scramble a signal coming from a sensor, so that only a person with the correct key can possibly read the data from that sensor. The sensor itself and the system of ...
0answers
29 views

### Crypto library that supports ElGamal PET and Mixnets

I am looking for a crypto library that supports VOTING primitives. Specifically: - Zero-knowledge Proofs - Mixnets - ElGamal Plaintext Equality Test (PET) - Commitments UniCrypt is one of the ...
2answers
62 views

### How does BLAKE2 ensure that hash(A) != hash(B) when B = A||0 and both A & B have the same number of blocks?

Suppose I have two arrays : A = a single byte, being zero. B = two bytes, both being zero. B = A||0 (i.e. B starts with A, and differs only by appending a zero byte) BLAKE2(A) != BLAKE2(B) Yet, ...
0answers
37 views

### Need some help to break a cypher text using unknown cypher [on hold]

I am a programmer and studied quite a bit of math, but I am a cryptography newbie. I browsed through this website, and I am awed. I need help decrypting a letter that was given to me as a ...
1answer
132 views

### Decrypt files with original file CTB-Locker

I have problem called CTB-Locker. It encrypted all of my files on computer and since I have lot of documents that are very important I am in problems! As I read online CTB-Locker uses "elliptical ...
1answer
61 views

### RSA: how does it work and how is it more secure than symmetric systems

Before starting the question, I know that RSA is naturally a key exchange cryptosystem rather than an antilogarithm fully implemented for encrypting and decrypting data since the length of the secret ...
1answer
57 views

### Will current encryption always remain secure? Is there mathematical proof?

Current encryption algorithms, such as AES, RSA, elliptic curve, etc. work based on known mathematical problems. I am specifically interested in the RSA. Will such security always remain secure? One ...
3answers
146 views

### Is there an oblivious decryption scheme?

Alice has $K$; Bob has $E(K, m)$; Is there such a scheme that enables Alice decrypts $E(K, m)$ without knowing $m$, and Bob gets $m$ ?
1answer
42 views

### Is it a variant of Strong RSA assumption?

Informally, the hardness of RSA/Strong RSA assumption lies in the hardness of factoring a large composite number $N$ having two large primes as its factors. If RSA modulus $N$ is a prime number, then ...
2answers
124 views

### Number of keys when using symmetric and asymmetric encryption?

Quoting part of my homework/assignment: How many keys are required for secure communication among 1000 person if: Symmetric key encryption algorithm is used? Asymmetric key encryption ...
1answer
25 views

### Cipher for human interpretation [duplicate]

Please suggest algorithms to encrypt and decrypt text messages that can be easily performed by human in a considerably short time. It doesn't have to be really secure, but sufficient to fool ...
0answers
26 views

### Decrypt Encrypted File on the fly and view to user

I have encrypted files on my Web server. Each file is encrypted with a unique symmetric KEY. All symmetric encryption keys are stored on db with public KEY encryption. On user side; Users are logged ...
2answers
778 views

### Is a small size block cipher usable?

Consider a block cipher with a key of size 128 bits but a small block size, say 32 bits. Is this kind of block cipher secure? I would like to know to what extent I can use a small block cipher, like ...
1answer
76 views

### Is the output of AES-CBC + MAC the same size as the input?

I use AES-CBC and HMAC-SHA256 to encrypt a text file. Will the output be larger in size than the input or will it be the same size? Is it more secure secure if the size of the output is larger?
1answer
48 views

### Achieving 32-bit verification code with 16-bit CRC?

I am programming an embedded chip that has a hardware 16-bit CRC module. I have to protect some data bytes $d_0,d_1,...,d_{n-1}$ against corruption caused by sudden loss of power; a 32-bit CRC would ...
3answers
13k views

### How should I calculate the entropy of a password?

If part of the password is a whole regular English word, does the entropy of that part depend on the number of English words in existence, the number of English words known by the choosing algorithm, ...
1answer
29 views

### Is it possible: Derived key based on variable number of private keys?

I have a MySQL database that I want to encrypt with AES_ENCRYPT() and have to provide access to a variable and possibly changing number of users. Is it possible to derive an encryption key based on a ...
2answers
81 views

### How does RSA padding work exactly?

I've read everywhere online and people say plain text RSA is very unsafe. To make it safe you pad it but no examples are shown anywhere on how to do it. It's explained that random data is added to the ...
2answers
87 views

### Finding strong primes

Wikipedia lists the following conditions for a prime to be strong: $p-1$ has large prime factors. That is, $p = a_1 q_1 + 1$ for some integer $a_1$ and large prime $q_1$. $q_1-1$ has large prime ...
0answers
35 views

### Why do Certificate Authorites cross-sign each other? [on hold]

In cryptography, a Certificate Authority (CA) issues digital certificates to certify the ownership of a public key by the named subject of the certificate. What is the rationale for CAs cross-signing ...
1answer
39 views

### What is contained in a RSA key file? [duplicate]

Consider a RSA key file like this: ...
2answers
571 views

### How to use GCM mode and associated-data properly

I'm currently migrating a project to use the bouncy castle GCM mode. I understand that using an authenticated mode removes the need for a HMAC, however I want to be sure that I'm using this mode ...
4answers
119 views

### Computation indistinguishability questions

The definition I have is: Two probability ensembles $X = \{X_n\}_{n \in \mathbf{N}}$ and $X = \{Y_n\}_{n \in \mathbf{N}}$ are computationally indistinguishable if for every probabilistic ...
0answers
29 views

### Which of these cipher suites is more secure? [on hold]

In an application that will transfer sensitive data over TLS to an online server, which of these cipher suites will provide the best long-term protection (assuming the transmission will be sniffed by ...
2answers
29 views

### Combined message separation

I have two ciphertexts, I suppose that its RC4 with reused key. I have XORed both ciphertexts and obtained message containing combined cleartexts. I suppose that the underlaying messages are written ...
1answer
48 views

### Converting a number to a member of a multiplicative cyclic group

I am currently trying to make an implementation of the ElGamal encryption for educational purposes. As I understand it, when using the encryption with multiplicative cyclic groups, one generates a ...

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