# All Questions

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### common ways / methods to try to break a SP network

I have a very little cryptography background (but a relatively solid maths background) so my below question is very general. Basically I have been given a SP network with an output to reverse. I ...
24 views

### AES or Serpent-Twofish-AES [on hold]

I want to encrypt my private stuff like credit cards, money, RSA private keys (and so on) but I don't know if I should use AES-256 only or in combo like Serpent-Twofish-AES (I am using Veracrypt). ...
15 views

### Using the Vigenere Cipher to find key

Given a ciphertext message that was generated using the XOR cipher and a bit string found in the plaintext, how can you find the key that can be used to map the plaintext to the ciphertext?
43 views

### Can machine learning analyze random number generator?

I'm studying for random number generators(RNG) and I saw about machine learning a few days ago. So I searched analysis of RNG using machine learning. But I couldn't find such fields. Are there such ...
36 views

### Encode-decode with different block sizes? [on hold]

I am implementing AES-ctr encryption. While encrypting I call dofinal on every 16 bytes of data. When I try to decrypt this data in different chunk size say 32 bytes I get different output (original ...
65 views

### zendo data size restrictions

zendo is a new mobile phone app which encrypts messages using a one-time pad: http://techcrunch.com/2015/03/24/one-time-pads-ride-again/ users have to meet in person and exchange a key via a qr ...
151 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 ...
26 views

### Is it secure to transmit a short plaintext with its MAC?

I have a short (32-bit) message that needs to be authenticated. Due to the constraints of my platform, I would like to use Speck32/64 (32-bit block, 64-bit key) with a Matyas-Meyer-Oseas one-way ...
45 views

### NTRU Encryption

It's using Euclidian inverse. Can you show it step by step? $$N=7, q=11, a = 3+2X^2 -3X^4 +X^6$$ the inverse of $a \pmod {11}$ is $$A=-2+4X+2X^2 +4X^3 -4X^4 +2X^5 -2X^6$$ How do we compute $A$?
49 views

### Does perfect secrecy imply uniform ciphertext distribution?

I suspect the answer is no, but I am not able to either prove it, or provide an example. In Katz and Lindell's book, it is only said that with a perfectly secret encryption scheme, the plain and ...
26 views

### Discrete log accumulator without pairings

Here $g$ is some fixed generator of a discrete log group. I don't want the group to be bilinear for efficiency and BDH-skepticism reasons. Is anyone aware of a discrete log accumulator? What I mean ...
29 views

### Blum primes [x=3(mod 4)] zero knowledge proof?

Lets say we have 2 primes, $p \equiv q \equiv 3 \pmod{4}$, and we make $n=p \times q$ public. I can, without revealing factors, show that $n$ has two prime factors. How can i zero knowledge prove ...
72 views

### Cycles in SHA256

In the recommendations, it seems cycles is used usually as in "CPU Cycles", but, that's not what I mean here. What I mean, is this: Let's say I start with a particular 256 bit value. Call this v. I ...
8 views

### How to import key BLOB generated from Microsoft CryptExportKey from Linux [migrated]

I have a private/public key pair saved as key BLOBs which were in fact exported with the Microsoft "CryptExportKey" API. Now I need to use the same key pair (specially the public key) under Linux ...
69 views

### Are modes of operation algorithms practical?

I took a cryptography class back in college, and now that I am working my 1st career one of the things currently on my plate is coming up with an algorithm to encrypt data before it's placed on the ...
62 views

### Hash function such that fx(hash(s1),hash(s2)) = hash(concat(s1,s2))

First, I'm not a mathematician, so I may express this question awkwardly. Feel free to chuckle. I'm wondering if there exists a hash function h such that for given strings s1 and s2, and string ...
54 views

Suppose to have a function for numbers expressed in 8-bit $\in [0,2^8-1]$ defined as: $$f(x)=x||x||x||x$$ where $|f(x)|$ is exactly 32 bits. e.g., suppose x=2 (00000010) so ...
41 views

### Authentication using a one-time pad

I am building a small embedded system of two nodes that communicate wirelessly. The microcontrollers I'm using are very limited: they only have 256 bytes of RAM. I would like to be able to ...
140 views

### What is this cryptosystem called?

From a paper Outsourcing Large Matrix Inversion Computation to A Public Cloud (IEEE Transactions on Cloud Computing, Vol. 1, N°1, 2013; alternate source requiring registration; preprint), I got to ...
32 views

### Linear Recurrence, keystreams, and periods

I am trying to understand the following problem: Consider the following linear recurrence over $Z_2$ of degree four: $z_{i+4} = (z_{i+3} + z_{i+2} + z_{i+1} + z_{i}) \bmod 2$ i >= 0. ...
6k views

### Now that quantum computers have been out for a while, has RSA been cracked?

D-wave systems has released a commercially viable quantum computer. This means in theory, that all asymmetric encryption algorithms — such as RSA — are now useless due to the speed at which quantum ...
37 views

### Twofish encryption in Python [on hold]

I have a test tool which uses Twofish as the encryption algorithm to encrypt data before sending it to the server. The code is written in C++ and uses Bruce Schneier's optimized C implementation ...
37 views

### Bit commitment, two blobs with same bit, without revealing it?

Suppose we have bit commitment scheme: $n=p*q$ and $t \in QNR_n$, with Jacobi $(\frac{t}{n})=1$ Commitment(P), random $x\in \mathbb{Z}_n$, $y=x^2t^b$, where $b$ is bit. Ok, suppose we have $y_1$ and ...
57 views

### How does ECDHE_RSA key exchange mechanism work?

Using Wireshark, I found these data exchanged with google.com over TLS: Client Hello possible cipher suites and possible curve types (eg. secp256r1) sent Server Hello cipher suite selected ...
51 views

### Is the SEED blockcipher still secure?

I did found an old question which answers exactly this but it is from 2 years ago and i was wondering if there were any changes. I have not been able to find any new information on the cipher and am ...
57 views

### Security aspects of using a global values as nonce and additional data for AES?

is it a good idea to use global values as nonce / additional data? What problems can occur? What should be take in account when we deal with such parameters for encryption. Thanks
41 views

### feistel structure? why decryption is so easy with reverse order of subkey

I am doing an assignment on writing own encryption and decryption algorithm..so i come across feistel structure...can someone explain to me why we only use reverse order of key in decrpytion and we ...
2k views

### Is it possible to make time-locked encrytion algorithm?

I'm not sure if what I'm asking is even a valid question but here goes. Would it be possible to add a mechanism to an encryption algorithm that would mean it had to be a certain time of the day or a ...
27 views

### Which homomorphic encryption is better for random key generation? [on hold]

i am developing an encrypted file using random key homomorphic algorithms which algorithm is best can any one suggest
117 views

### Proving the existence of a pseudorandom function

I've been reading the Introduction to Modern Cryptography book by Katz and Lindell as part of my own learning and have come across this exercise which I am not sure how to approach. The exercise is: ...
49 views

### Why calculate pi to estimate randomness?

Why do testing suites calculate pi using the Monte Carlo method to determine if a series of numbers are random? As far as I can tell, the Monte Carlo method can be used to estimate pi itself (as a ...
128 views

### Is it an example of bilinear pairing?

Consider a bilinear pairing $e: G_1 \times G_2 \rightarrow G_T$. Let's assume, $G_1 = G_2 = G_T = (\mathbb{Z}_n,+)$, i.e. additive group of integer modulo $n$ and $e(x,y) = xy$ mod $n$. Isn't it an ...
47 views

### Credit card number encryption using AES counter mode [duplicate]

I want to encrypt 1000 credit card numbers, and I want do it with AES counter mode. Shall I send the nonce separately and not send it along with ciphertext? Is it possible to use dynamic keys with a ...
203 views

### Compact digital signature for noisy data

The question asks for a signature scheme, with a public verification procedure, that is tolerant to minor alterations of the signed data during its transmission [possibly in analog form over some ...
10 views

### Paillier algorithm encryption [migrated]

Can any one tell me how to implement paillier algorithm for an file that i am uploading this is my code.. ...
131 views

### Is Encryption without knowing the input directly possible at all?

I know the question is rather unusual, but let me clarify what I'm searching for: There is one person, lets call her $Alice$. $Alice$ has $n$ plaintexts $t_1..t_n$ and $n$ public keys $pk_1..pk_n$ of ...
74 views

### What is the best hash for HMAC?

Long question but I am starting to lose sight of all the HASH algo's there are. I know SHAKE128 and 256 are part of the SHA-3 standard but is the SHA3 standard officially released yet? i can only ...
21 views

### cryptographic hash function [on hold]

Consider an ideal cryptographic hash function H : {0, 1}∗ → {0, 1}n, in other words, H takes a string of arbitrary length and returns a string of n bits, and it is assumed that H acts like a “random ...
44 views

### Should I remove these use cases of MD5/SHA1 from my program?

I have a web app (a register and login system) written already but i am now improving it. One of its design goals was high security. I have some use cases of md5 and sha1 in it and now i am in doubt ...
50 views

### Is it safe to use PBEWithMD5AndDES?

I'm encrypting some of my (not so much important) files with PBEWithMD5AndDES. Is it a strong method or it can be de-crypt easily without knowing my selected ...
21 views

### Key Confirmation Attack [Key Distribution Center (KDC)]

Okay this is how I understood it according to this: Alice $A$ establishes a connection to $KDC$ and prepares for session key Exchange $k_{ses}$ $A$ encrypts the request with her key $k_A(A, B)$ ...
41 views

### Is it safe to encrypt data by simply randomizing chunks based on a permutation?

Say I want to encrypt the following text: "Today is March the 22nd, 2015". And say want to encrypt 8-byte blocks of data using the following permutation [6,3,0,1,5,7,2,4] to swap characters at those ...
66 views

### credit card number encryption using aes-ctr mode

I want to encrypt credit card numbers. I want to apply AES-CTR mode. Is it suitable for that? How can I store nonce and counter values for an individual credit card number? How can I send the ...
30 views

### security of pairing based cryptography

while going through some papers on cryptographic accumulators i find the following statement "several pairing-based accumulators have been proposed in the past. However, due to continuous and recent ...
74 views

### Why would using a random seed with other variables be bad for ecrypting if you can't guess the key?

I asked this on stack exchange with it being code based, but someone suggested to ask here. Basically, I've done a script in python and wanted an option to encrypt the input, but I couldn't get any ...
8 views

### Using ssh agent to sign a string [migrated]

I am trying to learn more about asymmetric keys. I am writing a program that uses ssh-agent server to sign a message. This works well, but it generates a RSA-SHA1 signature of the message, which I am ...
23k views

### How can I use SSL/TLS with Perfect Forward Secrecy?

I'm new to the field of cryptography, but I want to make the web a better web by setting up the sites that I host with Perfect Forward Secrecy. I have a list of questions regarding the setup of ...
4k views

### Is there a simple hash function that one can compute without a computer?

I am looking for a hash function that is computable by hand (in reasonable time). The function should be at least a little bit secure: There should be no trivial way to find a collision (by hand). For ...
54 views

### How are RSA and ElGamal compatible in PGP?

I'm starting to play with PGP and I don't understand how if your key pair is RSA you can encrypt a message for someone whose key is for example ElGamal. How does the asymmetric key exchange work if ...
434 views

### SHA-1:Is there any mathematical result that gives us the minimum number of 1's in a 160-bit SHA-1 hash output?

Is there any mathematical result that gives us the minimum number of 1's in a 160-bit SHA-1 hash output? What is the probability that a 160-bit SHA-1 hash output contains at least 128 1's?

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