# All Questions

24 views

### OpenSSL Signature different each time

I have a file that I am generating a signature for using OpenSSL, and each time I generate the signature, it is different to the last time. ...
25 views

### 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. ...
193 views

### Simulation based proofs: Simple examples

I am aware that,(in theory) in order to proof that a scheme is secure using simulation based proof we replace an adversary in real world with a simulator in ideal world. Then we try to show that their ...
24 views

### 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 ...
21 views

### Poly1305 vs VMAC: is VMAC much better for long messages?

VMAC seems to me much more secure than Poly1305 on long messages (the security of the latter decreases linearly with increasing message length). Is this of practical relevance?
39 views

### AES128 Decryption in Objective-C just slightly off

I have been asked to integrate a home-grown CRM system with a 3rd-party data service provider (DSP). The DSP has encrypted the information they are providing. I only have their decryption ...
81 views

### How to find roots of equation $f(x)=0 \pmod p$, where $p$ is prime number?

$f(x)$is any nth degree equation $n>0$, how to find roots of $f(x)$ over prime modulo.
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### Is multiplicative blinding less secure than additive?

It's easy to see that additive blinding (e.g., $x+r$ for secret x and random r) is perfectly secure in a finite field (this is a one-time-pad) and statistically secure for $r$ uniformly distributed in ...
23 views

### block cipher secure as ind - cpa

if we have the following block cipher found here http://imagebin.ca/v/2WGa2kAGEX3E, is it ind - cpa secure?
24 views

### Updating values authenticated by Merkle Tree

Assume we have 4 values: $v_1,v_2,v_3$ and $v_4$. We construct a Merkle tree on top of them such that the values are leaves of the tree. I send the values and the tree to an untrusted server. But I ...
63 views

### What is wrong with simple concatenation in salted password hashes?

I once heard that if implementing a password hashing scheme, simply concatenating the password and salt together before hashing could lead to some subtle vulnerabilities, and I'm trying to figure out ...
22 views

### Miller Algorithm of Weil Pairing implementation for Python2

I would like to implement miller algorithm for Python, but it cannot work correctly, Please help me. (1) Please tell me Miller algorithm's output of the following case. ...
782 views

### Is there a null HMAC?

I came up with this question while unit testing a function that includes an HMAC. What is the expected behavior of an HMAC with a well-defined key and a set of data with no elements in it? Is there ...
98 views

### Common Modulus Attack not reproducible

I want to calculate a simple example of the RSA common modulus attack. However, the result is not correct and I do not find my mistake. p=$29, q=37, n=p*q = 1073, \phi(n) = 1008, e1 = 5, e2 = 11$ ...
29 views

### Cardholder to Merchant SET Protocol

I have some doubts regarding the SET protocol. Let say the Alice payment information runs through a sha-1 hash function which is a one-way algorithm, irreversible to create a message digest. How do ...
35 views

### Compression in key generation of DES algorithm

Does anyone have a pseudo-code or an algorithm or even a diagram of the compression (pc2) of the DES algorithm? I can't find a relation between the bits that are dropped, even when I do it manually ...
58 views

### How to encrypt incomplete block with RSA as a block cipher?

I have a question about an RSA academic example. If we are using block-RSA with a block-size of 3 and we have this message: "android". It is broken into 'and', 'roi', 'd'. How to encrypt the last ...
23 views

### SET Protocol (SET)

I would like to know if the current SET protocol uses 3DES or AES other than DES and RSA? I have look into many articles but some of them were outdated.
42 views

### Encryption of Real Time UDP packet

I am planning to work on real time UDP packet encryption. I have a server which generates fixed size UDP packets at every 200ms and this message is sent to the receiver application which receives this ...
127 views

### Why does a non-prime DH modulus creates a “NOBUS” backdoor

can't we do a nobus backdoor with DH modulus prime? Some have argued that with a prime modulus you can just get the order by doing p-1 and then factor it, thus it is easy to reverse. I argue that this ...
197 views

### elgamal based decryption mixnet

Can anybody help me to understand elgamal based decryption mixnet? Pure elgamal can be used in mixnet (re-encryption mixnet) and its very easy, and I have implemented decryption mixnet using RSA also. ...
52 views

### How do substution-permutation networks work? [duplicate]

I understand what is going on in higher level. But I don't understand what's really going on in page 3 and 4 of this slide. Specifically, How $S_0$ and $S_1$ is used? What goes in what goes out? ...
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### How to break Universal Re-Encryption algorithm?

Let p be a prime, and g be an element of $ℤ^*p$ of prime order q. Let x ∈ ℤq be the private key, and $h = g^x$ (mod p) be the public key. To encrypt a message m ∈ $ℤ^*p$, pick two random ...
71 views

### How to prove that a function F isn't a pseudo random function

Let $F$ be a length-preserving pseudorandom function. For the following constructions of a keyed function $F' : \{0, 1\}^n \times \{0, 1\}^{n−1} \to \{0, 1\}^{2n}$, state whether $F'$ is a ...
111 views

### HW acceleration for Camellia cipher (x86_64/AES-NI/AVX2)

Modern processors support hardware acceleration for various crypto functions such as AES directly, or general vector operations which can be used in crypto ...
32 views

### Does Coppersmith's method always finds non-trivial factor of integers of the form $n=a(2^k b+1)$ assuming $1 < a<2^k b +1$ and $b < n^{1/4-0.05}$?

Crossposted from mathoverflow. Got an argument and numeric evidence that pari's implementation of Coppersmith's method finds non trivial factor of integers of certain form under some assumptions very ...
41 views

### ECDH-ECDSA Combination

I am doing research on cryptography primitives at a basic level and I faced a question on encryption methods. I understood that ECDH is an approach to for secure key exchange between two parties ...
1k views

### HRNG for One Time Pad

I have just advanced to the last grade of high school (in Denmark). In this year, we all get to do one big project, where we can build/invent/create whatever we want to "solve a problem". As I study ...
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### How to convert AES to a PRNG in order to run NIST Statistical Test Suite?

I want to run statistical tests on my implementation of AES. How should I convert it into a PRNG? Is there a standard way to go about doing this? I could not find much information about this although ...
22 views

### Comparison Affine Coordinates and Projective Coordinates Addition in Excel

Kurve : EC : y^2=x^3 + x + 1 Generator:(1,7) p=23 Result in Affine use excel: P=(1,7), Q=(7,11) => P+Q=(18,20) Result in Projective use exccel: P=(1:7:1), Q=(7:11:1) => P+Q=(15:2:9) U = U1 - U2 ...
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### Secure randomized data matching?

This might be a dumb question but I will go for it. Let's say we have a data set $D$ consisting of sensitive data, and we want to be able to match if a new piece of data $S$ already exists in $D$ ...
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### How do I solve this transposition cipher? [on hold]

(88 characters): ANNHA MSUIM HDSHP CEVVA LEOVE PAERS ADYSC TNLIE LIIET PTSRO CNAFM GONCO NMAMO RLEIT MSNSY LFOOI SASEO RGA. -- My introductory cryptography instructor assigned this, I calculated the ...
177 views

### Why was the Navajo code not broken by the Japanese in WWII?

In reading about this topic recently, to my understanding, the encryption schemes used on top of the Navajo language were very simple and definitely could have been broken (my research shows they ...
57 views

### How to generate a random number so server cannot cheat?

Here is the protocol: Bunch of players connected to server. Server creates nonce and hashes it - send hash to clients as bit commitment. Clients make nonces and send hashes to server as their bit ...
29k views

### Are there two known strings which have the same MD5 hash value?

Is there an example of two known strings which have the same MD5 hash value (representing a so-called "MD5 collision")?
3k views

### How many RSA keys before a collision?

I was wondering how many possible private/public keys exist? If a million people – for whatever reason – would try to generate 5 keys each in the same minute (on the same date and time) is there a ...
408 views

### How to do a literature search

How do I do a literature search of the research literature on cryptography? Assume there's some topic in cryptography I'd like to learn more about; how do I search the cryptographic research ...
39k views

### Should we MAC-then-encrypt or encrypt-then-MAC?

Most of the time, when some data must be encrypted, it must also be protected with a MAC, because encryption protects only against passive attackers. There are some nifty encryption modes which ...
59 views

### Performing simple arithmetic operations on compressed, and both compressed and encrypted data

We all know it is possible to perform addition and multiplication operations on encrypted data by means of homomorphic encryption methods. My questions are: Is there any cryptosystem that is able to ...
74 views

### Is IPsec IND-CCA secure provided the used block cipher is a pseudorandom function?

I am trying to solve the question whether "IPsec is IND-CCA secure provided the used block cipher is a pseudorandom function" (with IPsec using a variant of Encrypt-then-MAC) As a resource I am given ...
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### Use precomputed value (ECPoint,int) in Java BouncyCastle [migrated]

I am working with window-method multiplication in affine coordinates. Window Method ...
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### Would the rotors in Enigma machines always advance by one position? Or was there a way to set this?

Before encrypting a letter the first rotor advances by one, right? So there could be a way, once the first rotor turns 26 times, make the second rotor advance two positions instead of one. Or three. ...
53 views

### Why Generate Keys are inside game

I am studying reductions to prove security of crypto systems. Generally are used "games" for the proves. For example, the next image is extracted from the page 91 of the book Postquantum Cryptography. ...
55 views

### Does key renewal increase complexity of MAC forgery?

Suppose I have encrypted messages sent to a device authenticated with a MAC keyed with a strong shared cryptographic key. This device can only process so many messages per unit of time. This ...
63 views

### Homomorphic Encryption with Addition and Exponentiation

Is there any homomorphic encryption scheme which supports addition and power over cipher text ? Paillier is close but it supports addition and multiplication with a constant. I am getting an output ...
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### Can OTP be made practical by using stretched hash algorithms? [duplicate]

One of the main reasons for not using OTP in everydays life is that it is highly impractical - for encrypting 4GB of files we need a 4GB key that needs to be exchanged secure. I've had an idea on how ...
126 views

### What is the difference between SHA-3(Keccak) and previous generation SHA algorithms?

SHA-1 and SHA-2 share the same structure and mathematical operation as their predecessors - SHA-0 and MD5. Both SHA-0 and MD5 have been broken. This is one of the main reasons why SHA-1 is considered ...
135 views

### How to show something is not a one-way function?

Lets say that $f:\{0,1\}^* \to \{0,1\}^*$ is a strong one way function. Let $h(x)=f(x)||x_n$ where $x_n$ is the $n$th bit of $x$. I understand that $h$ will not be a strong one-way function. However, ...
Our goal is find a faster discrete Gaussian sampling to solve $"SVP"$ problem in lattice: A lattice is discrete subgroup of $R^n$ such that define as below: let $\{b_1,\cdots ,b_n\}$ be a basis in ...