0
votes
1answer
62 views

Breaking One Time Pad with CCA

I was taught that: although OTP is CPA secure, it is not the case with CCA. I'm trying to figure how to break OTP with CCA by showing how it fails the IND test. ...
0
votes
1answer
25 views

Are chosen-prefix collisions for SHA-1 a major threat?

GPG signing of Git commit tags relies on the collision resistance of SHA-1, which is weak. However, the attacker does not get to choose the prefix. How much does this translate to an actual ...
0
votes
1answer
24 views

A simple keyed message authentication code using XOR

Suppose I have a key that is at least 32 characters in length and provides at least 128-bits of entropy. If I picked from the character set of [a-hjkmnp-z2-9-], ...
0
votes
1answer
24 views

Uniqueness of checksums using DES-MAC encryption?

I'm in an Intro to Computer Security class, and one concept I'm having trouble understanding is how two different files could produce the same checksum. How would you produce the same checksum given ...
0
votes
1answer
39 views

Three-Pass Protocol number theory

I've got a homework problem that I'm having a hard time understanding. It's for the Three-Pass Protocol, and we are given p, the three messages, and are told that the original plain text is one of two ...
0
votes
1answer
153 views

Cube-Root attack - RSA with low exponent

I have this RSA public key ...
0
votes
2answers
111 views

Is this method of encryption theoretically unbreakable?

I implemented a Stream Cipher using Cryptographically Secure Random Numbers for the key values. The key stream was as long as the plaintext stream. This key data set won't be reused. Have I met all ...
0
votes
2answers
41 views

How to find element g order q, given 2 large primes p and q where q|p-1

i have calculated 2 large primes, $p$ (minimum 2048 bits) and $q$ (minimum 224 bits), where $p-1 \mod q = 0$ by using SageMath. $p = ...
0
votes
2answers
164 views
0
votes
1answer
39 views

Attack being kind of completely puzzled?

I am reading this paper "The security of Hidden Field Equations (HFE)" and at the end of the page 4 the author wrote: Thus, after all, this belief about every attack being kind of ”completely ...
0
votes
2answers
82 views

How to show that this modification of CBC-MAC is insecure?

I'm working on some cryptography problems, found this and I'm not sure how to solve it: Modify CBC-MAC so that all blocks $t_1,\dots,t_l$ are output rather than just $t_l$ and prove it is not ...
0
votes
1answer
23 views

Probability of generating same master secret key in Identity-based Encryption

Suppose multiple servers use same IBE domain parameters (I mean same curve description parameters and field) for master secret key setup. Is there any possibility for generating the same system ...
0
votes
1answer
32 views

Is there an algorithm that allows verification that 2 encrypted or hashed bits of data are the same, given that I may only know half of the key/ salt?

We have an interesting problem. Currently, we store a salted hash of some secret key known only to the clients of our clients to allow us (and our clients) to find other records that were generated ...
0
votes
1answer
50 views

Key derivation using the main AES encryption key and some plain text

I am using AES 128 bit encryption in java. I have an encryption key and 10 digit plain text. I want to derive a key for HMAC using the AES encryption key and the 10 digit plain text. This plain text ...
0
votes
1answer
49 views

Mathematical Proof for Key independence in Differential Cryptanalysis

How would you construct a proof that XOR difference of two cipher texts cancels the influence of the key? I started out with a simple cipher defined as follows: $C = \Phi( S(P\oplus K_{0}) \oplus ...
0
votes
1answer
104 views

What is a branch number in the PAEQ algorithm?

I'm reading an article about authenticated encryption algorithm - PAEQ. It uses a permutation function AESQ, which has transormations from AES. And there is written about MegaSBoxes, which contain 4 ...
0
votes
1answer
61 views

How to decrypt RSA if ciphertext is less than the modulus and e=3?

I'm given a public key. Using openssl rsa ..... I got the public key has the exponent as 3. When I calculated the size of the ciphertext, it is 8 bits smaller than the 2048-bit modulus. How can I ...
0
votes
2answers
47 views

Gaussian function in lattices

Probability density function of gaussian distribution is $$ 1/{\sqrt{2 \pi} \sigma} \times {e^{{(x-c)^2/ 2{\sigma}^2 }}} $$ in lattices we assume $$ \sigma =s/\sqrt{2 \pi} $$so the gaussian ...
0
votes
2answers
45 views

Order and cofactor of the base point? [duplicate]

What is the order and cofactor of a base point? Is it possible to deduct the order and cofactor, given just the basepoint. What about the other way around from order and cofactor to basepoint?
0
votes
1answer
47 views

Difference between HMAC-SHA1(key, msg) vs SHA1(key + msg) [duplicate]

Is there any practical difference from using HMAC-SHA1(key, msg) vs SHA1(key + msg) as a way to verify the ...
0
votes
1answer
62 views

Hardware optimized stream ciphers?

As I understand it, ChaCha20 is slower than AES-CTR in hardware. Are there any hardware-optimized stream ciphers?
0
votes
1answer
58 views

Proving a function is a one way function

I am trying to prove that a function is a one-way function. The function I am working on in particular is $f'(x,y)=f(x)||f(x \oplus y)$. For what I have understood looking at similar solved ...
0
votes
1answer
54 views

Why does a hacker need to crack the key to an encrypted file, instead of just brute forcing the password? [closed]

Most encryption softwares don't seem to have a trial limit. So why would a hacker need to crack the key, or even need to know the salt value, if he can just brute force the 6-8 digit password?
0
votes
1answer
31 views

One Step Decryption For Multiple Chained Encryptions

If we have a encrypting function f(x, y) (x for input, y for key) and let's say we composite this function n times inside itself with the same y (like f(f(f(x, y), y), y)) and set the output to be z. ...
0
votes
1answer
56 views

Is there an additive homomorphic encryption that supports exponentation

For example say we have two numbers a and b. Now is there any partial homomorphic encryption scheme that allows to compute (a-b)^2 over the ciphertexts of a and b without round trips.
0
votes
1answer
33 views

Is there any place where I can find test vectors for point addition and doubling of ECC?

I want to extensively test my implementation of point addition and doubling. I have only one test vector with me. I need more values to test. In the web, I could find test vectors only for key pair ...
0
votes
1answer
45 views

How to encode a message to MD5?

I have faced a problem to understand MD5 algorithm.My question is weather the original input message is converted to binary value in MD5 before using the input message as parameter in four Feistel ...
0
votes
1answer
26 views

Inverse in ElGamal signature

I am learning about ElGamal signature verification. During the signature generation one has to choose a k such that ...
0
votes
1answer
64 views

Scalar multiplication with projective coordinates

I'm implementing point addition, doubling and scalar multiplication using projective coordinates. I took reference from this link https://www.nsa.gov/ia/_files/nist-routines.pdf I have implemented ...
0
votes
2answers
40 views

digital signature on image and text

i am trying to implement an android app that should "sign" an image, M and a string, S using a private key, K-1 and send the result to a server. for instance the app should be doing {M,S}K-1. the ...
0
votes
1answer
27 views

IPSec recomendations about rekeying

IPSec like strongSwan can be configured to do rekeying after time or bytes transferred or packets transmitted. Is there any recommendations to set those settings? Maybe according to algorithms used?
0
votes
1answer
26 views

Vulnerabilities in specifying the hash algorithm used for signature verification on a per-message basis

Let's say that I have a 4096-bit RSA key and when I sign data, I typically use SHA-512. As far as I understand it, the hash algorithm used to sign/verify a message is specified in the message. If a ...
0
votes
1answer
61 views

How Diffie-Hellman authentication works? [duplicate]

There are a lot of good videos on a simple Diffie-Hellman in the internet but unfortunately that is susceptible to the MITM attack. I understand how with DH the two parties are able to calculate a ...
0
votes
1answer
32 views

Determining collision resistance of a function?

I am having trouble trying to understand if the function is collision resistant. As I understand it, preimage resistance means that it is hard for an adversary to find two messages that produce the ...
0
votes
4answers
179 views

How is a message digest decrypted?

Trying to get my head around digital signatures and hit a slight block. The book I am using gives the following information Device A hashes a message to create a message digest Device A encrypts ...
0
votes
3answers
67 views

What is the time requirement for pairing computation and modular exponentiation?

I want to design a cryptographic protocol for encrypted search without pairing. I have seen some papers for protocols without pairing. How would I compare pairing computation and modular operations?
0
votes
1answer
49 views

“Royal Flags Wave Kings Above” [closed]

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
1answer
86 views

Multiparty encryption and decryption

Is it possible to send a single encrypted data message to multiple users so that the users receiving the message can only decrypt certain parts of the message, depending on their rights. For example, ...
0
votes
1answer
53 views

Proof of Knowledge/Data Integrity using Hash Function

Objective: A verifier wants to ensure that a block of data M is also known to a prover. The protocol should exchange little information and should not leak information about the value of M. Proposed ...
0
votes
1answer
65 views

Finding a secret cipher given the key and known plaintext?

Let $x,y,k$ be plain text, cipher text and key respectively. Also suppose $\operatorname{Enc}$ is the algorithm of encryption for block cipher with size $n$. So we have $$\operatorname{Enc}_k(x)=y$$ ...
0
votes
1answer
44 views

Block cipher detect padding behaviour

Suppose i have a crypto provider, i.e: i give that provider some plaintext bytes and get the encrypted result. I don't know the used encryption method, but i know ...
0
votes
1answer
64 views

Can BPS be used to encrypt a single integer, and restrict the output to a certain range?

As per specifications document, "We have the natural restriction that at least two characters must be ciphered, i.e. $b \geq 2$" where each character is represented by an integer of certain ...
0
votes
1answer
35 views

Lagrange Coefficients & Polynomial in KP-ABE

My question is how these concepts relate in ABE. I am assuming that the attributes are used to share the master secret key and only a user with the right attributes for a particular access tree is ...
0
votes
2answers
105 views

Why IV does not have to be secret yet has to be random [duplicate]

The IV used in schemes such as CBC has to be random and unpredictable. But at the same time it does not have to be kept secret. If the IV does not have to be secret, why does it have to be random ...
0
votes
1answer
27 views

Would buffering socket send resist timing attacks

I have been reading and thinking about timing attacks on cryptographic systems. The answer to this question mentions the following: "The way to defend against timing attacks is to make sure the time ...
0
votes
2answers
58 views

Stateless proof-of-work system with 0-roundtrip time

I'm designing an API. To avoid abuse, I need to rate limit the requests somehow, but I don't want to do it per user as it's very easy to create new accounts automatically. I think a proof of work ...
0
votes
1answer
70 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 ...
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
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. ...
0
votes
1answer
39 views

can session key be be used as digital signature?

if two communicating parties share a (symmetric) session key, k. When one of the party wants to send a message 'm' to other, is it okay use {m}k as a digital signature?

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