3
votes
1answer
171 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
105 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
48 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
112 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
174 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
63 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
51 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 ...
3
votes
2answers
196 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
144 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
236 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
247 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
54 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
110 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
67 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
83 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
110 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
117 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
69 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
82 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
132 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
75 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 ...
3
votes
0answers
44 views

Cost of attack on DSA with attack on DLP

Are there any (recent) estimates of cost of attack on DSA by solving the discrete logarithm? I'm especially interested in attacks that use Pollard's rho algorithm. Are there any optimized ...
1
vote
0answers
23 views

802.1X Radius WLAN protected by certificate 1024-bit key

I want to ask you a question. I have WPA-2 (enterprise) network. Also called as 802.1x. I use the Linux Zeroshell distribution, which is optimized for these services. Linux Zeroshell is provides a ...
3
votes
2answers
138 views

Security analysis of this one time password based scheme for copy protection

Imagine such protocol. Client and server initially share secret K[0]. When client wants to contact server she sends server K[0] and her ID. Server accepts request, and generated new random K[1] and ...
2
votes
1answer
58 views

Which algorithm would be ideal for ephermal key generation followed by DH key exchange?

Bob and Alice, both generate a temporary public key pair each using X algorithm on their individual PC. After being authenticated by a third party, they use the DHE to come to get a common symmetric ...
6
votes
2answers
722 views

On AES, is a true random string enough for a key?

The string (32 ASCII characters) is entered by a human, and considered truly random. Should a key derive from this string, or it is secure to use this string as a key directly? In other words, does ...
2
votes
0answers
65 views

How to compute projective cordinate Z in elliptic curve cryptography?

I was working on affine coordinates and struggling with the computation time taken for operations and then I was advised to use projective coordinates so that mul-inverse operation can be avoided Can ...
3
votes
2answers
73 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 ...
3
votes
1answer
117 views

Public key exponent coprime with totient proof

I read this question a while back (In RSA, why is it important choosing e so that it is coprime to φ(n)?). I was wondering whether there is a proof that shows that a public key exponent e that is ...
1
vote
0answers
32 views

What do you mean by Ciphertext indistinguishability [duplicate]

Wiki definition : A cryptosystem is considered secure in terms of indistinguishability if no adversary, given an encryption of a message randomly chosen from a two-element message space ...
2
votes
2answers
399 views

Why is hybrid encryption more effective than other encryption scheme?

Currently I am learning about Hybrid Encryption but I was not able to find any good study material. Below is my understanding: One of the reason why we use ...
4
votes
1answer
62 views

Information theoretical security of an inefficient Shamir based access structure

I have studied Sharmir's scheme as well as the multiple assignment scheme proposed by M. Ito. My question is if anyone can tell me if the following scheme is theoretically secure: Terms: P = set of ...
5
votes
1answer
54 views

How to show CPA attacker does not need access to encryption oracle after receiving cyphertext

In the private key CPA game, the attacker has access to an encryption oracle anytime during the attack. However, I have seen this statement in lecture notes I downloaded "You can prove that for ...
3
votes
0answers
43 views

How does darkmail (DIME) work to hide email metadata?

While Email encryption can protect the content of an email, the metadata are still readable and can be used to gather important information about the sender and the receiver. There were several news ...
0
votes
0answers
47 views

What are the negative consequences for choosing 8 S-boxes for DES vs 1 S-box for AES?

DES has 8 different S-boxes, and AES has only 1. What are the negative consequences of such choices?
0
votes
1answer
30 views

Why is it that in DSA, the order of the subgroup, $q$, is chosen such that it divides $p - 1$?

Consider the DSA key generation: A large prime $p$ is chosen; A smaller modulus $q$ is chosen such that $p - 1$ is a multiple of $q$; A generator $g$ s.t. $\operatorname{ord}_p(g) = q$ is chosen. ...
1
vote
1answer
311 views

MiTM on RSA public key encryption

a) Alice just generated a new pair of public and private RSA keys (pkA , skA ) = ((N, e), d) and would like to start a private conversation with Bob. How can Alice interact with Bob and exchange a ...
1
vote
1answer
60 views

How is the ciphertext labeled with a set of attributes in Key-Policy Attribute-based Encryption (KP-ABE)

My question is about Key-Policy ABE (KP-ABE). What does it mean when a "Ciphertext is Labeled with set of attribute"? How is it labeled?
4
votes
1answer
41 views

Blake2: truncate 512-bit hash is safer than 256-bit by Config?

I need to calculate 256-bit hash in my code, using BLAKE2. I know I can set BLAKE2 to generate itself a 256-bits hash for any data but I´m curious to know what can be safer and faster: 1- Create the ...
12
votes
1answer
174 views

Structure for an introductory course on cryptography?

Many introductory courses on cryptography have their treatment of secret-key crypto start with OTP, then block ciphers, and for public-key cryptography revolve around RSA with no notion of padding ...
1
vote
4answers
312 views

Message exchange with textbook RSA

I am working on this exercise but can't work out the answer to the question b. I have solved the question (a) by decrypting the ciphertext $C = 2$ using the formula: $$ M = C^d \bmod n = 2^{17} \bmod ...
0
votes
0answers
31 views

NTRUSign Hashing

I have some trouble understanding the inner workings of NTRUSign. So what I have understood so far is, that when Alice wants to sign a message she does the following steps Convert Alice's message ...

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