# All Questions

0answers
6 views

### CBC related TLS cipher suites to be disabled in the server side

I understand the TLS cipher suites using CBC mode are susceptible to timing attacks. From that understanding it seems that the cipher suites using GCM (CTR-based) are safe to use considering they don'...
1answer
32 views

### Do I understand HMAC-SHA-xxx and HMAC-SHA-xxx-yyy correctly?

I've recently started looking at HMAC, and there a few things that I'm not 100% sure that I'm understanding correctly. Am I right about these three things? HMAC-SHA-xxx has an output length of xxx ...
2answers
19 views

### Does the Server Key Exchange sign a hash or text

In TLS 1.2 when using ECDHE_RSA, the ServerKeyExchange message contains a signature over the server's ECDHE public parameters. My question is: Is the signature over ...
2answers
27 views

### Newbie - Hybrid Symetric and Asymetric

Just looking for a bit of an explanation on the concept of hybrid symmetric and asymmetric encryption. My understanding: Client requests public key from https://site1.com The client receives the ...
0answers
28 views

### Double DES meet in the middle attack: probability that wrong key pair remains

My Question is based on poncho's answer in this post. If you're doing a meet-in-the-middle attack against 2DES with only on a plaintext-ciphertext pair $(P,C)$, I understand that the expected amount ...
0answers
12 views

1answer
35 views

### Does hashing an encrypted message suffer from any drawbacks?

I am working on this problem where the set up is like this: There are three hosts: A, B and C. A wants to send a message to C which passes through B. At A the message is hashed, the hash is padded to ...
0answers
27 views

### How to proof that this cipher is perfectly secure?

I am new to Computer Security and I am trying to solve the following exercise: Consider the following encryption function which transmits one letter. Let n be a fixed positive integer. The ...
0answers
24 views

### the password is incorrect while its correct [on hold]

i want to test my login page but i used password encryption before password was saved in the database. if i try to enter from login page will display error message "Incorrect password or email". and ...
0answers
46 views

### Hamming distance of any vector to 2 different sets is a constant

Let $\mathbb{F}_2^n$ be an $n$-dimensional vector space over the field $\mathbb{F}_2 = \{0, 1\}$. Assume that I have 2 sets $A, B \subseteq \mathbb{F}_2^n$ which have the following property: there ...
1answer
21 views

### Why are computations (isogeny) in SIDH done in an extended prime field?

While reading the SIDH key exchange protocol, I noticed that all the isogeny computations and curves are defined over the extended prime field $\mathbb{F}_{p^2}$. Does it make the problem ...
1answer
38 views

### Computing/using RSA modulus without knowing its factors

There are some protocols, e.g. this, that require parties to compute/use RSA modulus: $N$ without knowing it's factors or $\phi(N)$. One way of doing it is to use a trusted party. Question: Is ...
1answer
62 views

### Newbie question: one-way functions in cryptography

I'm reading this article on the basics of cryptography and it says that the main principle is about taking such an algorithm that knowing the end result and the algorithm, an eavesdropper wouldn't be ...
0answers
5 views

### DOS 6..2/Windows 98 encryption software [migrated]

Is there any encryption software (full disc encryption or container mode) available for Windows 98? Same question for plain DOS 6.22. Maybe it's strange, but for some reasons I need software like that....
1answer
42 views

### Patent Status & Usability of AE Modes

Post Structure: Sources Cited Question & Details Before You Answer Useful Info From Comments Sources Cited: https://blog.cryptographyengineering.com/2012/05/19/how-to-choose-authenticated-...
0answers
20 views

### Understanding a security error with RC4 using the same key to encrypt on the client/server sides

This apparently was a bug with WhatsApp a while ago. I am endeavoring to recreate it and understand it. The bug had to do with the fact that the same key was used to encrypt plaintext on both the ...
0answers
30 views

### Applying Chinese RemainderTheorem and Paillier Homomorphic encryption

I'm trying to optimize the decryption process for Paillier Homomorphic Encryption (PHE) using the Chinese Remainder Theorem (CRT). However, I want to check if there's a different way of applying CRT ...
1answer
64 views

### Why RSA must make sure that $\gcd(e,\varphi(n)) = 1$ instead of $\gcd(e,n) = 1$?

By Euler's theorem, if $\gcd(e,n) = 1$, then $e^{\varphi(n)} \equiv 1 \pmod n$. But why does RSA need to make sure that $\gcd(e,\varphi(n)) = 1$?
0answers
42 views

### How to derive a hash function from another hash function?

Problem: I'm trying to figure out how to solve this, apparently it's hashing the hash value itself. So G has two rounds of hashing the original message x. I tried searching for the relationship ...
0answers
20 views

### Encrypted output from an embedded device?

Does this look like encrypted output, please? { 811 #2D #CC29 #C102 #E9 #B5 #C62 E01 #C8 #2139 #68F1 #08 #A6 #672 241 #8C #0E29 #8642 #86 #C6 #262 E61 #4B #0E29 #A942 #...
1answer
25 views

### problems decrypting alphanumeric characters to original text

I'm using openSSL aes_cbc128 to encrypt/decrypt some text coded in C++. When I run with only numeric data, everything is fine. When I run with alphanumberic data, the last block does not decrypt to ...
1answer
34 views

### how Content Scramble System (CSS) works?

As I understand, the Content Scramble System (CSS) uses proprietary 40-bit stream cipher algorithm to decrypt the DVD content My question is; where does this key come from? is it embedded within the ...
2answers
38 views

### McEliece post quantum cryptography

Can someone explain me in basic simplistic english if possible how does McEliece asymmetric encryption works and why its quantum safe ? Thanks in advance.
0answers
44 views

### What lightweight cryptographic hash function for short input could I use for HMAC?

I am looking for a cryptographic hash function that I can configure for HMAC. The input that I will hash is around 50 bytes. The function must be fast, and computationally lightweight.
1answer
153 views

### Is SHA1 secured enough as a PRNG

I read SHA1 is still a secured hashing function with no collision found as of now. However, it's just a matter of time for someone to come up with such a collision or attack. Therefore, in new ...
1answer
37 views

### Instead of sending a set of random values, send a key for a PRF

Some Protocols require one party to send $n$ random challenges (or random values) to another party. For communication efficiency purpose, one can pick a random key for a pseudorandom function, and ...
0answers
23 views

### WebCrypto AES-GCM vs AES-KW for key wrapping

The Web Crypto API available in most browsers supports both AES-GCM and AES-KW for key wrapping. There are examples for AES-KW and AES-GCM performing key wrapping, and a popular live table indicates ...
0answers
9 views

### IEEE P1363-3 Identity-based Cryptography schemes simulation

I am researching possible implementations of IEEE P1363-3 Identity-based Cryptography schemes (https://books.google.gr/books/about/IEEE_P1363_3_D9_May_2013.html?id=IADLnQAACAAJ&redir_esc=y ) and ...
0answers
10 views

### Asymmetrical encryption with multiple sufficient key-pairs [duplicate]

I have the following requirement: There are N public/private RSA key pairs. The encrypted data must be decryptable by any of the private keys alone, but not by any other key. For encryption, the ...
0answers
7 views

### Multi Party Protocol - Proof with semi-honest adversaries

I have designed a protocol where one entity acts as a "client", sends information to one of many "server-parties". This second party sends some other information to another "server-party" and so on, ...
0answers
18 views

### Implementation of EVP AES 128 CTR using openssl library

How should I provide counter value in order to test my algorithm with the standard test vectors given in IETF Tools? Code snippet: ...
2answers
37 views

### KDF Salt: How/When is it Okay for it to be public?

Post Structure: Prior source material studied Question & Details Assumed threat model Example Assumptions Clarifications Prior source material studied 0.1. RFC 2898 0.2. HAC (Handbook of ...
0answers
28 views

### breaking aes, time taken using quantum computer? [duplicate]

Let say we want to break aes-256 using a quantum computer, that would take 2^128 operations using groove algorithm. Now let say we have a 128 qubit quantum computer, can this be broken instantly ? If ...
1answer
28 views

### MPC on boolean circuits

I am reading about Yao's and GMW protocols and was wondering if there is any perfectly secure MPC protocol in the semi-honest setting, where the underlying circuit is a Boolean circuit (eg. n=3 and t=...
0answers
47 views

### Double encryption : what method is the best?

Given the block-ciphers defined as follows : $1.$ $C=$ $E_{k1}($$E_{k2}$$(M))$ $2.$ $C=$ $E_{k1{\oplus}k2}$$(M)$ $3.$ $C=$ $(E_{k1}(r),E_{k2}(r$ ${\oplus}$ $M))$ where $C$ is the cipher ...
0answers
29 views

### Leveraging patterns in ciphertext

I've got a cipher I believe to be polyalphabetic, which may or may not have a key in which I've discovered some patterns, and I'd like to know how I can use these patterns to try to understand how the ...
1answer
39 views

### Commitment in two party protocols

I have been reading Fast Secure Two-Party ECDSA Signing by Lindell, and I see that in key generating and signing (pages 9-10, especially visible from Figure 1), only the first party performs a ...
1answer
56 views

### Blowfish padding

I'm currently reverse engineering a binary that uses Blowfish. A sample input would be: 08 00 01 00 1C FB 19 00 When this data is encrypted and then decrypted, I ...
5answers
2k views

### Is a PRG more costly than AES or any other encryption standard?

I know that there are many encryption standards that take a key and sometimes an IV, and produces a cipher-text (the most prominent one is AES). These standards usually involve many rounds of addition ...
1answer
51 views

### Practical quantum attacks on SHA256 MAC and HMAC

Is SHA256 MAC (or HMAC) vulnerable to any quantum attacks? Game setup: The attacker's goal is to produce a valid MAC to be accepted by other devices in the ecosystem. The ecosystem consists of ...
1answer
59 views

### Regular and Efficient doubling in $GF(2^n)$

A naive approach to compute a multiplication $a \cdot b$ in a Galois field of the form $GF(2^n)$ is the russian peasant algorithm. However, it does not run in constant time and therefore is not safe ...
1answer
27 views

### Who assigns algorithm OIDs for cryptographic algorithms?

I am aware that this is at the border to security but I guess that I will rather find an answer here. The question is which institution generally assigns object identifiers for cryptographic ...
1answer
35 views

### A feasible approach for AEAD on an ethernet link?

The setup is shortly this: There are two custom switches (think of an FPGA for example), both are handling 10-100 Gb/s orders of traffic from their outside facing interfaces. This is normal traffic. ...
1answer
20 views

### Location of header fields within a OpenPGP message

I'm trying to understand the structure of a OpenPGP message in detail. Therefore I generated a test message and parsed it using gpg --list-packets. The output is ...
0answers
8 views

### Asyncronous Rachet tree: How user movability is handled is the Rachet tree being recreated?

As I have read the latest state of art in group key agreement is the Asyncronous Rachet Tree. But in applications like IRC that exists high user movability (users join in ans leave the room). Is ...
1answer
68 views

### GUIDs as a salt

Quote: Most of these answers are a bit misguided and demonstrate a confusion between salts and cryptographic keys. The purpose of including salts is to modify the function used to hash each user's ...
0answers
36 views

### Questions about Private Oblivious Transfer Protocol

The receiver R chooses $a,b,r$ and computes as follows: If σ = 0 then $A = (g^a, g^b, g^{ab},g^r)$. If σ = 1 then $A = (g^a, g^b, g^r, g^{ab})$. R sends $A$ to S. Denote $(x,y,z_0,z_1)$ the tuple ...
3answers
67 views

### Variation on the ECB Penguin problem

So this is an age-old example of why encrypting images with ECB is a terrible idea, since the underlying pattern of the image remains the same. Referenced from: If you encrypt an image (AES), is it ...

15 30 50 per page