Cryptography Stack Exchange
Cryptography Stack Exchange

Questions tagged [symmetric]

Symmetric cryptosystems assume two communicating entities share a pre-established secret key.

Symmetric cryptosystems assume two communicating entities share the same secret key. Symmetric secrets are generally used for encryption (block ciphers, stream ciphers) or authentication (MACs).

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Rubik's Cube as Encryption

Consider this scenario: Alice gets a Rubik's Cube and peels off the colors from each piece. She then writes a small message on one of the faces of the cube and fills the remaining pieces with random letters. Then, she scrambles the pieces in a way…
yasar
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Do key collisions for symmetric ciphers exist?

I'm not sure if I'm calling the thing (key collisions) correctly, and that's probably why I couldn't find any information about it on Google. Still, my question is as follows. Note that I don't work with encryption right now and I'm not going to…
Vladimir Matveev
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uniquely identify a symmetric key

Is there a safe way to uniquely identify a symmetric key? I know with asymmetric keys you typically use a hash of the public key, but I assume that using a hash of a symmetric key would reveal too much information. Would you simply have to assign…
senecaso
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Is CTR more secure than CBC?

In cryptography, a block cipher mode of operation is an algorithm that uses a block cipher to provide information security such as confidentiality or authenticity. A block cipher by itself is only suitable for the secure cryptographic transformation…
moyu
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What is the best way to store sensitive information on the client?

I am very inexperienced with cryptography and would like some advice on how to store some sensitive information on client machines. I have some information stored in a central database on my server. A snapshot of this database is distributed along…
Kevin Craft
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Simple Electromagnetic Analysis vs symmetric cryptography

I've asked this question here and was advised to post this question on this forum in hopes of an answer. I'm currently taking a security class and i came into this issue when writing a report about side channel attacks. When reading about…
user201305016
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Proper encryption algorithm to use when encrypting data before backing it up to untrusted hosts?

I'm writing a (non production/proof of concept) backup program that takes files from your computer, splits them into blocks, and then has other peers store those blocks to create an offsite backup. Those peers could be other parties that you would…
Azendale
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Using the same symmetric key in both directions?

A simple symmetric encryption scheme uses the same key, derived from a password, for both directions of the communication. Is this bad practice, and if so what should be done about it? Is it 'good enough' for many things?
Ken - Enough about Monica
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Why have 4th and 5th steps in Needham-Schroeder Protocol?

Why have 4th and 5th steps in Needham-Schroeder Protocol? It is said "These steps assure B that the original message it received (step 3) was not a replay.". But what is a replay here? And I don't actually get what those 4th and 5th steps do. Send…
evening
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Is the polynomial system representation of a symmetric cipher overdetermined?

Is the representation of the polynomial system of a symmetric cipher overdetermined?
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Verifying affine spaces in Xoodoo component

I am reading "The design of Xoodoo and Xoofff". On page 13 there is a collorary related to the component $\chi$ [Algorithm 1, 1]. Corollary 1. For fixed (difference or mask) $a$, the compatible (difference or mask) $b$ values form an affine space…
juaninf
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What does a linear function with huge order mean?

I am reading this paper "Farfalle: parallel permutation-based cryptography", and there are some terms that I do not understand. Page 4 says ratio efficiency vs. safety margin. What does ratio efficiency and safety margin mean? Page 5…
juaninf
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Prepend information about encryption implementation to the stored data

I want to preface this by saying i will not be using any of this code/information in a live project, this is only for learning/fun (so I welcome some speculation) I was looking at how the PHP crypt() function works, and i had an idea. crypt()…
Klathmon
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Why probabilistic syntax for encryption schemes?

In Foundations of Cryptography II, Goldreich, the basic mechanism of encryption schemes is written as follows: Definition 5.1.1 (encryption scheme): An encryption scheme is a triple, $(G,E,D)$, of probabilistic polynomial-time algorithms satisfying…
Chris
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WEP - shared symmetric keys

I know that WEP uses stream cipher encryption. The key stream = RC4(IV, K). My question is: The shared symmetric key is the same for all users? Or each user has it's own symmetric key. Also, how can a user get this key?
Jorge Martins
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