2
votes
2answers
17 views

What are possible caveats when generating a group for use as parameters for Diffie-Hellman key exchange?

As reusing a widely used group for Diffie-Hellman key exchanges might lead to far easier third-party key discovery through precomputation for that specific group, I would like to know what can ...
0
votes
0answers
8 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. ...
0
votes
2answers
16 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 ...
4
votes
3answers
84 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=$29, q=37, n=p*q = 1073, \phi(n) = 1008, e1 = 5, e2 = 11$ ...
2
votes
0answers
20 views

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 ...
1
vote
1answer
34 views
1
vote
1answer
25 views

Research for video game: Novice cryptography concepts

I'm making a video game which has some basic cryptography as a main base for puzzle design. I'm hoping players will get great puzzle challenge and learn a few cryptography concepts through playing the ...
1
vote
1answer
19 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 ...
1
vote
1answer
21 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 ...
1
vote
2answers
46 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 ...
0
votes
0answers
15 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.
-1
votes
0answers
34 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 ...
2
votes
2answers
102 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 ...
1
vote
0answers
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. ...
3
votes
0answers
39 views

How do substution-permutation networks work?

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? ...
-4
votes
4answers
88 views

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 ...
2
votes
0answers
56 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 ...
3
votes
2answers
103 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 ...
3
votes
1answer
30 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 ...
1
vote
1answer
36 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 ...
7
votes
3answers
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 ...
3
votes
1answer
53 views

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 ...
1
vote
1answer
20 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 ...
1
vote
2answers
68 views

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 $D$ ...
-1
votes
0answers
22 views

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 ...
9
votes
2answers
9k views

What is the difference between MAC and HMAC?

In reference to this question, what are the "stronger security properties" that HMAC provides over MAC. I got that MAC requires an IV whereas HMAC doesn't. I also understood that MAC may reveal ...
6
votes
1answer
151 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 ...
3
votes
2answers
51 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 ...
35
votes
7answers
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")?
10
votes
2answers
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 ...
8
votes
2answers
407 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 ...
166
votes
10answers
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 ...
5
votes
1answer
54 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 ...
6
votes
1answer
72 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 ...
-1
votes
0answers
10 views

Use precomputed value (ECPoint,int) in Java BouncyCastle [migrated]

I am working with window-method multiplication in affine coordinates. Window Method ...
-2
votes
0answers
21 views

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. ...
3
votes
2answers
52 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. ...
4
votes
1answer
51 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 ...
0
votes
1answer
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 ...
0
votes
1answer
31 views

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 ...
3
votes
2answers
122 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 ...
0
votes
2answers
134 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, ...
1
vote
1answer
42 views

“Royal Flags Wave Kings Above” [on hold]

I'm a starter to cryptanalysis and in fact to cryptology. Last night I was decrypting a message from a book that I would quite odd. It doesn't make sense. The decrypted message is "Royal Flags Waves ...
0
votes
0answers
28 views

construction of division polynomials

I'm not sure if this is the right place for my question.... I'm trying to understand the construction of the division polynomials used in the schoof algorithm. I firstly followed the report of ...
1
vote
0answers
21 views

Faster discrete Gaussian sampling

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 ...
3
votes
1answer
21 views

Merkle tree (dm-verity) with SHA-256 vs. SHA-1

Is there any knowledge or research on the use of different hash functions within a Merkle tree? My use case is file integrity protection. I am thinking about using different hash functions due to ...
3
votes
1answer
21 views

Deriving a key for HMAC, using PBKDF2

What is the recommended way to derive a key for an HMAC-SHA256, from a passphrase and salt? I'd like to compute an HMAC-SHA256. I have a passphrase, and a message. I note that RFC-7518 (JWA) ...
4
votes
1answer
96 views

Generating random vector for Full Homomorphic Cryptography

The site below explains that part of doing homomorphic encryption, you need to generate a vector of random numbers that have the property that its dot product against a randomly generated bit vector ...
12
votes
1answer
860 views

How does a non-prime modulus for Diffie-Hellman allow for a backdoor?

Recently someone found that a Diffie-Hellman modulus used in a unix tool (socat) was not prime. This led some people to shout "backdoor". What I don't understand ...
1
vote
2answers
35 views

NIST HMAC Test vectors

I am searching test vectors of the HMAC-SHA256 primitive to verify the correctness of an implementation. Without hesitation I go on the NIST website to see what they offer. While reading the ...

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