0
votes
1answer
36 views

How to understand authenticator working process [closed]

Now days authenticator are used widely, however as a beginner to cryptography, I'm confused on the mechanism of key refresh. How it works ? Is that related to DH-key-exchange or the server will change ...
1
vote
1answer
121 views

How to select $g$ in Paillier Cryptosystem

For my cryptography class project in university I have selected Paillier Cryptosystem as a course project ...
-1
votes
1answer
55 views

How do they implement MAC in TLS?

I recently read questions about "MAC then Encrypt/Encrypt then MAC" which made me curious about how they actually use the algorithm. MAC only calculated once either case (according to what I read). ...
1
vote
1answer
76 views

Sequence of Encrypting RSA like Chaum Blinding scheme

I'd be a noob in cryptography but reading up a little on RSA, I do get some understanding and I want to specifically resolve this issue. UPDATED Lets say we have the following values in place: ...
1
vote
0answers
49 views

A known-plaintext attack on an LFSR-based stream cipher

I am reading a book about Cryptography, and I am stuck in a question. I am really trying to solve it for weeks. But I think the problem is I couldn't understand the whole picture. The question was ...
0
votes
2answers
87 views

Perfect Forward Secrecy in TLS

I read that TLS does PFS using Diffie Hellman. However, DH can be used even without certificates - so how is DHE-RSA better than plain DHE? Is DHE a insecure algorithm, that DHE-RSA is needed?
1
vote
0answers
56 views

How we can said a crypto system have perfect secrecy?

For example: I have 3 plaintexts ($a$, $b$, $c$) and 4 keys ($K_1$, $K_2$, $K_3$, $K_4$), making a table map to the cipher text, key as row and plaintext as column $\begin{matrix} \ \ \ \ \ \ \ \ \ \ ...
1
vote
2answers
95 views

Why do some block cipher modes of operation only use encryption while others use both encryption and decryption?

In Chapter 6, Question 6.8, of his book “Cryptography and Network Security Principles and Practices”, William Stalling asks: Why do some block cipher modes of operation only use encryption while ...
3
votes
0answers
120 views

Security of RSA for paranoids with padding?

RSA for Paranoids (RSAP) (in cryptobytes v3n1), also known as Unbalanced RSA, is a variant of RSA proposed in 1995 by Adi Shamir, as a mean to increase the RSA public modulus size while keeping ...
1
vote
0answers
55 views

El Gamal encryption scheme and symmetric encryption scheme

Consider the El Gamal encryption scheme, a symmetric encryption scheme (KG,E,D), and the following hybrid encryption scheme having an encryption algorithm that, on input a public key (G,q,g,h), where ...
2
votes
1answer
90 views

Why does HMAC need a fixed length padding?

As everybody knows in order to calculate HMAC we have to concatenate padding to the message. I am just curious why the padding needs to be fixed-length. Why do we need the blocksize parameter here? ...
0
votes
0answers
53 views

New modulus or new key pair?

I have this assignment question that I'm not sure how to answer. Any insight would be helpful. In the RSA public-key encryption scheme, each user has a public key, e, and a private key, d. Suppose ...
1
vote
1answer
41 views

Disadvantages of one-way accumulators?

One-way accumulators are built upon a (quasi)-commutative one-way function. With quasi-commutativity, I refer to the following property: For $f : X \times Y \to X$, it is true that $f(f(x, y_1), y_2) ...
0
votes
0answers
54 views

Basic Encryption Tests [closed]

For study purposes I have created a block cipher as a bit of fun. Everything appears to be working really well to me, but what steps are normally taken in investigating whether an encryption algorithm ...
4
votes
1answer
124 views

Why are collision attacks important when talking about MAC schemes?

I'm reading Ferguson, Schneier, and Kouno's Cryptography Engineering, and it has a section on MACs. It discusses different types of MACs, but it seems to claim that to acheive 128-bit level security, ...
1
vote
1answer
43 views

Showing that security of a elgamal invariant is insecure

Original Elgamal signature is defined $S(m, \alpha) = (r, s)$, where $$r = g^k \bmod p$$ $$s = (m – r*α)k^{-1} \bmod (p – 1)$$ more information on Elgamal signature can be found here. Variant ...
3
votes
1answer
123 views

Given a message and signature, find a public key that makes the signature valid (ECDSA)

This question is a variant on Given a message and signature, find a public key that makes the signature valid, which discusses the analogous question for RSA. It was suggested to me by this post over ...
4
votes
2answers
104 views

security in the standard model → random oracle model?

Can a protocol proved secure in the standard model be considered secure in the random oracle model?
2
votes
0answers
177 views

implementing a cryptographic hash with a block cipher [duplicate]

How can a cryptographic hash function be implemented/created using the block cipher? I was wondering if we can use AES in cipher block chaining mode to implement it.
0
votes
0answers
38 views

Open SSL signatures - merkle ecdsa rsa [closed]

I want to sign/verify a file over open ssl using these three algorithms. Is there a way to measure the time?
-1
votes
1answer
57 views

How to keep phi(n) secret in RSA?

As we know, RSA cryptosystem have both private key(a,p,q) and public key(b,n), by chinese remainder theorem and fermat's little theorem, we know that the importance of keep p and q secret, and from ...
1
vote
1answer
121 views

How do I express each element in a field F as a power of a primitive element?

I have a field $\mathbb F_{2^4}$, and it is represented as a residue ring of the polynomials over $\mathbb F_2$ modulo the polynomial $\beta^4 + \beta^3 + \beta^2 + \beta + 1$. I want to express ...
1
vote
0answers
67 views

How we transfer 128bits cipher to a 4x4 matrix for AES input?

Why the input cipher for AES encryption, can write in 4x4 matrix with 8 bits entires, and can said is 128bits? if each cell is 8bits in binary, how we said this matrix is represent 128bits?
-1
votes
0answers
53 views

What is the asymptotic complexity of RSA and paillier cryptosystem algorithm? [closed]

I want to know the complexity of the RSA and paillier cryptosystem algorithm in asymptotic notation.
2
votes
0answers
62 views

Threshold signatures vs. certificate authority+voting verification

Perhaps a silly question, but I am wondering what the advantages are of threshold signatures. Let's consider the following two signature schemes: $(t,n)$-threshold signature with a trusted dealer, ...
0
votes
0answers
59 views

After heartbleed, how can you safely distribute new certs? [migrated]

It's been a while since I studied key distribution, so I may have some fundamental misunderstanding.. From what I remember, man in the middle attacks can't occur during cert distribution because the ...
1
vote
1answer
76 views

Difference between plain AES CTR and “CCM-style” CTR

I am trying to adapt the following function from SJCL, which does "AES-CCM" style CTR encryption, to do "pure CTR" encryption. I am playing around with SIV and would rather use this well-reviewed ...
6
votes
1answer
156 views

Why does this square root algorithm work?

I've been doing some elliptic curve cryptography, and a library I'm using has this slightly bizarre algorithm for computing modular square roots: Let $x$ be some quadratic residue modulo $p$ for some ...
1
vote
0answers
27 views

Index of coincidence for completely random text over k alphabets

I'm confused about /Friedman's method 2 (using a table with column of k size of key, and n/k rows, n is the total size for cipher text) \begin{equation} m = ...
1
vote
1answer
134 views

Leak-proof protocol: is such a thing possible?

Is it possible to design a protocol that by itself guarantees that a malicious implementation cannot leak secret data without breaking the protocol? Setting: Alice and Bob have a pre-shared secret ...
4
votes
1answer
159 views

Is there an algorithm to check if an elliptic curve is secure?

As I understand it elliptic curves are of the form $y^2 = x^3 + ax + b$ Where $a$ and $b$ are the curve parameters. However not all parameters will give a curve suitable for crypto purposes. Is there ...
-1
votes
1answer
90 views

cryptography and use of python programming language [closed]

why is it recommended to write cryptography programs ,for example crypt-analysis projects with python programming language? what is the advantages of python? why not use c or any other language?
2
votes
1answer
192 views

Is there a simple zero knowledge proof of $x$ for $b=x^x\pmod p$?

We have a multiplicative cyclic group $G$ which is a subgroup of $(\mathbb{Z}/n\mathbb{Z})∗$. There are two parties, Alice and Bob: If: Alice knows: $b$ and $x$ such that $x^x = b$; Bob knows: $b$. ...
2
votes
0answers
78 views

An example of Knapsack Cryptosystem cracks/attacks?

I have been studying papers on various ways to crack the knapsack cryptosystem, unfortunately the mathematics in these papers involves lattices and LLL which is over my head. The paper "New Attacks ...
1
vote
0answers
64 views

Is this a correct understanding of Universal Hash Functions?

I'm studying universal hash functions and have been reading several papers but now i'm focusing on Wegman and Carters original paper from 1979 (Universal classes of hash functions) and the H1 class. ...
0
votes
1answer
38 views

AES-256 Shift-Rows Offsets

I am currently trying to implement a AES-256 cipher according to this sepcificaciton: http://techheap.packetizer.com/cryptography/encryption/spec.v36.pdf As well as on Wikipedia and in the document ...
1
vote
0answers
38 views

Reliability of a single-pass deniable authentication protocol?

I look for one-pass deniable authentication protocol with a short message payload for my project and find a solution: ...
3
votes
0answers
80 views

Security of this deterministic encryption scheme

I recently came across a library that promises to do deterministic encryption with the following scheme: AES with 256 bit key in CBC mode with PKCS7 padding and Synthetic Initialization vector ...
1
vote
0answers
20 views

Hill cipher key space

Key space is the set of all possible keys that can be used to generate a key.we using the number of valid key to describe it. Q: I've given a hill cipher of block size k over alphabet of size p, ...
2
votes
1answer
86 views

Rotation table for 8 round DES

I'm trying to implement DES from scratch using the NIST paper and the Wikipedia article on DES. I got 16 round DES done, but I can't seem to get 8 round DES working. I figure it's because I got the ...
1
vote
1answer
65 views

Why do we encrypt-then mac but sign-then-encrypt?

This question was asked in comments on my answer to should we sign then encrypt or encrypt then sign. I think posing the question as a separate entity is best, so: The general advice for applying ...
0
votes
0answers
49 views

How to know private key is computed from specific partial private key?

In a certificate-less cryptography, I have learned that – to resolve the key escrow problem of IBE – the concept of a partial private key is used. Now, consider the following Scenario: After ...
6
votes
2answers
642 views

Will repeated rounds of SHA-512 provide random numbers?

If I hash a keyword with SHA-512 and then feed the output as the key for the next round ....and keep repeating this process, will I gather a stream of random numbers?
3
votes
1answer
83 views

Zero-knowledge proof for committing a choice?

Let's say there are 100 choices (which are publicly known), each represented as a different string, and today you have to choose one of them. You need not reveal what that choice is right now, though. ...
3
votes
1answer
50 views

Does displaying HMAC hashes of user inputs compromise the HMAC validation?

Here is the scenario: "SECRET" is a secret key that is kept private and only used in this one application. The application allows users to enter in any "VALUE" (within various open-ended limits such ...
1
vote
1answer
45 views

Secret Sharing 1 Required

Devise a scheme so that a message M can be shared among X, Y and Z in such a say that the only way of recovering the message is when X is present with either Y or Z. When X isn't present or each is ...
0
votes
0answers
89 views

Hybrid encryption RSA with AES?

I made a hybrid algorithm using the elliptic curve theory. I want to compare my algorithm with another standard algorithm. I was thinking about using RSA with AES, where the AES key is used to encrypt ...
-1
votes
1answer
164 views

SHA256-based stream cipher

Can anyone comment if the stream cipher described here is safe? The author claims it to be unbreakable, but does not provide any evidence or proof to support this. For completeness, I have reproduced ...
0
votes
0answers
33 views

Locally Dedcodable Codes and Private Information Retrieval

Does anyone know about Locally Decodable Codes (LDCs)? It seems the private information retrieval schemes that based on LDCs are computationally efficent (answer a query without processing the whole ...
-1
votes
0answers
28 views

HKDF as keystream generator

This is not my design, but used in the onepw protocol used for the new sync scheme in firefox by mozilla. https://github.com/mozilla/fxa-auth-server/wiki/onepw-protocol In this scheme a key is ...

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