3
votes
1answer
100 views

Decisional Diffie-Hellman: compute Legendre symbol of $g^{ab}$ from $g^a$ and $g^b$?

From https://en.wikipedia.org/wiki/Decisional_Diffie%E2%80%93Hellman_assumption: Importantly, the DDH assumption does not hold in the multiplicative group $\mathbb {Z} _{p}^{*}$, where $p$ is ...
2
votes
1answer
58 views

Is (1 bit HW signal) XOR (8 bits PRNG output) sufficient for a HWRNG?

This is really a follow up question to a comment made regarding How to roll a HWRNG In the situation of whitening a hardware generated random bit stream, "XORing the two bitstreams should be fine ...
6
votes
1answer
91 views

What are the relative merits of padding algorithms pkcs7, iso7816, and x923?

I am assuming none of these padding algorithms are "the best"... But what are the advantages and disadvantages of using them? PKCS7 is certainly the most commonly used one, but I am interested in ...
3
votes
0answers
79 views

HD (Hierarchical Deterministic) Keys using Safe Curves?

Bitcoin's HD (Hierarchical Deterministic) Keys as described in BIP32 allow for a master key to be created (a private key and a chain code) such that a tree of both public and private keys can be ...
5
votes
1answer
76 views

Choice of the one-way function (OWF) for Lamport signatures

I am studying the Lamport signature scheme, and I found that in many sources (eg: Hash-based Digital Signature Schemes) the input and output bitstring of the OWF and the message digest have the same ...
4
votes
1answer
83 views

Can I store the initialisation vector (IV) in the filename?

I'm encrypting a file and I'm using an initialisation vector. Given that the IV doesn't need to be a secret, is it secure if I add it to the encrypted file's name?
2
votes
3answers
385 views

What do numbers in a crypto algorithm stand for? Is there a convention?

What do the numbers stand for in the names of cryptographic functions, for example AES-256, RSA-1024 or ...
1
vote
2answers
55 views

Clarification regarding multiple modular exponentiation

If the base is same and exponents are different, for example: $R_1=b^x\bmod{p}$; $R_2=b^y\bmod{p}$; $R_3=b^z\bmod{p}$; ($p$ is large prime (2048 bit); $x$, $y$ and $z$ - 160 bit integers)) To ...
6
votes
1answer
126 views

What is the difference between RCCA and CCA2?

Well, I know it's easy to tell CCA1 from CCA2, but I failed to find the difference between RCCA and CCA2. What is the difference?
1
vote
1answer
27 views

Secure Multiparty Computation with Secret Output

Is there any MPC scheme that allows a function with several secret inputs to be computed, while the output can only become known to one specific party? If not, is this even possible?
5
votes
0answers
118 views

Efficient way to confirm identity

I am working on a multiplayer game. I have a central server which handles all data transmission and coordinates all games. Clients which involved in a single session send requests to do actions to ...
4
votes
2answers
115 views

Is it okay to use an HMAC of the plaintext and a (possibly distinct) key as the IV for symmetric cryptography?

I was thinking of how to create an IV for a block cipher that doesn't require stored state, and I came up with the idea of using an HMAC of the (padded) plaintext and a (possibly distinct) key as the ...
4
votes
0answers
61 views

Why SIVP Is Worst Case Problem?

I just started to study lattice cryptography. I'm now studying worst-case to average-case reduction for SIS. In previous question, "worst means any and average means random". And I wonder why ...
2
votes
2answers
86 views

What is the purpose of Pseudorandom Function Families (PRFs)?

I'm currently in a course in Cryptography, and was wondering why pseudorandom function families exist at all. If there existed one pseudorandom function f(x), based on its definition, could that not ...
5
votes
1answer
61 views

Symmetric encryption algorithms with large IVs and authentication?

Most modern symmetric ciphers require a nonce/IV. If the nonce is reused, security is lost. If the nonce is large enough, it can be generated securely by using a CSPRNG. This avoids needing to keep ...
0
votes
1answer
121 views

Combining a block cipher with a (pseudo) OTP

One of the drawbacks of OTP is that it can require an inconveniently long key. Besides that, it doesn’t provide data authentication. Therefore, I have been working on an algorithm idea, which I hope ...
0
votes
1answer
72 views

How can I study the math behind cryptography? [closed]

I am a junior in high school and I am currently studying algebra 2. Where can I go to learn about the mathematics behind cryptography? I have a very basic knowledge of cryptography, but I am really ...
2
votes
1answer
105 views

Would SHA-1 be safe for certificates with short validity?

There are articles floating around the topic of SHA-1 deprecation. The gist of it is that in (mostly) developing countries, people are still using mobile/computing devices that are 5 years old (or ...
2
votes
1answer
286 views

Authenticated Encryption of UDP packets

I am working on a UDP based file transfer protocol. Congestion Control, Resending of packages and other UDP challenges are dealt with - speedtests shows that the protocol is up to 10 times faster than ...
1
vote
1answer
69 views

Username and Password: How does it work?

Suppose a client (Alice) goes to an HTTPS website (Bob) over TLS 1.2. Alice sends Client Hello with some random number $r_a$. Bob sends Server Hello with another random number $r_b$. Suppose they ...
2
votes
1answer
196 views

How is the AddRoundKey operation performed in AES-256?

Can anyone explain to me (or send a link to somewhere) how round keys are added in AES-256? I understand that the round keys is added to the state matrix for each round and how XOR works. But since ...
3
votes
1answer
172 views

Provable security of cryptographic hash functions

I am working on the following exercise question: Consider the following construction of a “keyed” hash function from Katz & Lindell (ex. 7.22 (1st ed.)/ 8.21(2nd ed.)). Gen : On input ...
2
votes
2answers
98 views

RSA and difference between factors

As I understand, for RSA $n = p \cdot q$. For the key to be safe enough from getting factored, $p$ and $q$ have to be far from each other. How far do they have to be? For example, if I have two ...
3
votes
2answers
114 views

Implementation of ECC over binary field

I am supposed to implement ECC over binary field (in C++) for equations of the type - $y^2 + xy = x^3 + ax + b$, as my project. I wish to include the following features : The user will enter a prime ...
2
votes
1answer
50 views

Generalization of the DL-assumption in bilinear group pair

When thinking about a pairing-based cryptographic scheme, I encountered the following problem. Let $e \colon G_1, G_2 \to G_T$ be a Type 3 pairing. Then: Given $P, zP \in G_1$ and $Q, zQ \in G_2$, ...
1
vote
1answer
116 views

How “hard” it is to take an e'th root mod p?

I know it's hard to find the $e$th root of a number mod $n=p_1*p_2$, and if it would be possible we could break RSA. But how hard it is to take an $e$th root mod $p$ where $p$ is a prime and ...
2
votes
2answers
175 views

Given a pseudorandom function F, is $(F_k(r) \; | \; F_k(r + 1))$ also a PRF?

Given: F is a pseudorandom function, G is a pseudorandom generator with $l(n) = n+1$. The following schemes should be classified as being insecure, IND-COA secure, IND-CPA secure. To encrypt $m \in ...
0
votes
1answer
67 views

Are there AES128 keys such that first round key equals last round key?

I am looking for AES128 keys such that the last round key is exactly the first round key (which is simply the key). Any pointer to a proof that they exist or that they don't would be welcome. In the ...
0
votes
0answers
52 views

Translation of Schorr Ring Signature to ECSchnorr Ring Signature

I have to write an EC version of Schnorr Ring Signature Scheme. I've already wrote regular ECSchnorr Signature Scheme using this (page 128). I've found a scheme of Schnorr Ring Signature Scheme (page ...
4
votes
2answers
201 views

Alice answering Bob without knowing the question

I'm a student and I don't know how to solve the following problem : Alice is proposing a 10 questions list to Bob. Bob choose only 1 question and wants to know the answer without Alice knowing the ...
3
votes
2answers
159 views

Best modern cipher for morse code?

I am looking for a modern cipher to encode morse code, ie. input is [A-Z 0-9] (base36 as I learned in the comments below) and output is the same, one character at a ...
0
votes
2answers
254 views

Lightweight Asymmetric encryption algorithm

I'm an embedded systems researcher, and new in the crypto field. Actually, I need to know if there are any lightweight asymmetric encryption algorithm especially considering the time needed for key ...
0
votes
0answers
14 views

Lightweight Asymmetric encryption algorithm [duplicate]

I'm an embedded systems researcher, and new in crypto field. Actually, I need to know if there are any lightweight asymmetric encryption algorithm especially from time needed for key generation. I ...
9
votes
2answers
260 views

Why use Diffie-Hellman key exchange over RSA (or any public-key encryption)?

In Diffie-Hellman key agreement between Alice and Bob, Alice computes and sends $g^a$ to Bob, and Bob computes and sends $g^b$ to Alice. Alice then computes $(g^b)^a$, and Bob computes $(g^a)^b$; ...
2
votes
0answers
55 views

Cyclic group collision resistant keyed cryptographic hash function

I am self-studying cryptography from a book and have come across a really difficult question that's doing my head in. I would be very grateful if somebody can help me out here with this difficult ...
2
votes
1answer
115 views

textbook RSA signature scheme security

Are textbook RSA signatures secure if an Adversary does not have access to ask signing oracle queries?
2
votes
1answer
69 views

Elliptic Curve ElGamal and DSA - smooth group order and element of large prime order

In regular ElGamal and DSA, we choose large primes $p$ and $q$ such that $p\equiv 1\pmod{q}$, and a group element $g$ of order $q$ by computing $a^{(p-1)/q}$ for some random $a$. This is to prevent ...
1
vote
0answers
17 views

RSA incorrectly translates for small keys [duplicate]

I've been learning about RSA and wrote my own implementation. I don't pretend to have intuitive understanding of RSA or that I understand why it works, but I believe to have some basic understanding ...
4
votes
0answers
84 views

Adding parameters to sponge's capacity

Is it safe to XOR parameters like domain, length of the message or block counter into sponge's capacity or that gives attacker control over capacity? For example NORX XORs domain into capacity. Does ...
3
votes
1answer
120 views

DES: How to find the Inverse of the Initial Permutation?

I am doing a DES problem by hand and I want to know how you calculate the inverse of the initial permutation. I know what the permutation is, but how do you find it based off the given initial ...
5
votes
2answers
124 views

Data Leakage and Data Switching

I have two secret values $a$ and $b$ (i.e. they are arbitrary values). I mask them as follow: $v_1=r_1a+r_2$ $v_2=r_1(b-a)$ where $r_1$ and $r_2$ are uniformly random values. I send $v_1$ and $v_2$ ...
4
votes
2answers
128 views

Hash functions vs Stream Ciphers in terms of Speed

We know that it's possible to create a hash using a stream cipher (for instance, RC4 or AES in Counter Mode). As stated here: "A Pseudo Random Generator (PRG) and a hash function are both Pseudo ...
2
votes
2answers
73 views

comparison of security for identity based signature and Hashing (SHA-1) the identities

I would like to know which method can provide better security: using identity based signature or hashing the identities and message (using SHA-1) for authentication?
1
vote
0answers
33 views

How to apply linear cryptanalysis to PRESENT?

Can someone help me implement linear cryptanalysis of the PRESENT block cipher? How should I start with 64 bits of plaintext and 80 bits of key?
3
votes
0answers
35 views

Seeking an implementation of the Satoh algorithm for elliptical curve point counting

I would be very grateful if someone has an implementation of the Satoh algorithm (Fast Elliptic Curve Point Counting). Can someone point me to practical algorithm implementations or provide some ...
1
vote
0answers
24 views

Generating keys in RSA [duplicate]

I'm trying to learn how RSA works. From what I found online, I'm supposed to generate private key using Extended Euclidean algorithm. I've managed to generate the public key, but don't know how to ...
11
votes
1answer
84 views

How to tell if a hardware RNG is rigged?

On a related note of building my own RNG, as someone suggested to use several commericial solutions how can I check if it is rigged against me? (although I am still strongly biased to a homebrew ...
-1
votes
1answer
33 views

Execution time for HMAC-MD5 on a 160 bit data using 128 bit key on a 3GHz CPU [closed]

I need to know the execution time for HMAC -MD5 for a 160 bit data using 128 bit key on a 3 Ghz CPU, kindly specify other parameters of the machine like RAM, operating system used etc
3
votes
1answer
133 views

How to determine if padding has been used while encrypting a message with RSA?

I am trying to decrypt a RSA encrypted text file. I have a 2048 bit public key. Analyzing the public key with openssl reveals the exponent used is 3. ...
4
votes
1answer
78 views

Is my pin algorithm secure?

I'm a hobby programmer and very new to this field. I opened a bank account recently and got two pins. One for the girocard and the other for a creditcard. And I needed two more pins for the online ...

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