Questions tagged [symmetric]

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

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How can I share a number with an opponent?

Let's say I have a message (eg: Hello, world!) and I want to encrypt this message using symmetric encryption (AES-256). I am using a list of keys, where I randomly ...
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0answers
223 views

The right way to encrypt sensitive data with an user password

I am developing something like 1Password and I want to be sure that method that I use is secure. Main idea of the app is storing user passwords, and is protected with a global master password. Main ...
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1answer
204 views

Deterministic symmetric indistinguishable encryption

Are there any block-cipher modes (or symmetric encryption schemes in general) that are fully-deterministic, meaning same inputs lead to the same outputs (like for all modes with constant IV) and ...
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4answers
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Is using the same IV in AES similar to not using an IV in the first place?

So if I understand how an IV works with AES, I'm supposed to generate a different IV for every message because using only a key, I will get the same encryption if the message was encrypted twice (...
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2answers
152 views

Broadcast encryption not using symmetric keys

Is there a common scheme for a broadcast style encryption that doesn't involve and exchange of a common key? I'm aware that traditionally what would be done is there would be a common symmetrical key ...
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1answer
80 views

Is symmetric encryption with a key containing the userId passes as authentication?

The scenario: There is a web application where ownership check is time expensive so during the development all users were able to access all other user's objects (let's say apples) by changing the ...
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0answers
101 views

Safely using ciphers that take small key sizes

Is it feasible to use triple encryption for block ciphers with the maximum keysize being the only significant security issue? I mean $C = E_{k_1}(E_{k_2}(E_{k_3}(P)))$ and $P = D_{k_1}(D_{k_2}(D_{k_3}(...
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1answer
113 views

What does GHASH really do?

I try to understand the GCM-MODE used in TLS. The problem I have had is described below. 1:textbook describes how GHASH works: 2: I get some debuginfo from openssl code that contain enc_key(32 bytes)...
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1answer
811 views

What is the main limitation of DES?

I know this question seems too general, not specific. Our professor asked this question today, and I have no idea how to answer it. Maybe it's the key size, maybe another thing? Any idea?
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132 views

Are sufficiently large key sizes enough to deter quantum attacks for symmetric key ciphers? [duplicate]

Are sufficiently large key sizes enough to deter quantum attacks for symmetric key ciphers such as AES?
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3answers
63 views

Establish more secure symmetric crypto system given A and B have small initial secret

Alice and Bob have a secret number X that is known only to them. However, the number is only 14 bits, and Trudy knows they share such a secret and can intercept messages between them. Instead of using ...
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1answer
916 views

If a key is used to encrypt that same key, is the computational cost to brute force it decreased?

If a key d is used to encrypt a message m that is identical to the key d, resulting in a cipher c c = encrypt(m, d) = encrypt(d, d) is the computational cost to brute force d lower than if the key d ...
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106 views

What is the computational cost of guessing symmetric keys for two ciphers that decrypt to the same input?

A message m is encrypted with two symmetric keys, resulting in two ciphers c, c1 = encrypt(m, key1) c2 = encrypt(m, key2) What is the computational cost of guessing symmetric keys for both ciphers ...
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2answers
202 views

Role of session identifier in Otway-Rees protocol

According to Wikipedia, Otway-Ress protocol is as follow: The protocol can be specified as follows in security protocol notation, where Alice is authenticating herself to Bob using a server $S$ ($M$...
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487 views

XOR and cipher stream

I am new to cryptography and I am very confused. In fact, I am so confused that I have trouble providing a suitable title for my thread... I know that a Substitution Cipher is designed to substitute ...
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1answer
104 views

How to solve rubix-cube like symmetric encryption

So for a project at University I wrote a symmetric encryption system that was very similar to how a rubix cube would work. I had each byte of my data mapped to a element in a grid, with 6 grids in ...
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2answers
201 views

Apply visual cryptography to a video stream?

I read that there are different ways to apply visual cryptography. One is to generate two images that when overlapped provide the original image. The main issue of using this approach with a video is ...
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1answer
369 views

Best method to achieve authenticated encryption with openssl

Problem I want to send a plaintext document between from myself to someone else over an untrusted link. I want to firstly stop third parties from reading the document, I want the receiver to be able ...
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1answer
504 views

Which cipher to use with openssl for shortest output?

I'd like to encrypt my 12-24 words seed for my bitcoin wallet with openssl command line tool to be able to have it with me on paper without the risk that somebody could use it Which cipher should I ...
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1answer
691 views

In BBC Sherlock's The Blind Banker, what type of cryptographic function is used by the Black Lotus?

In BBC’s Sherlock, Season 1, Episode 2 “The Blind Banker”, the Black Lotus crime syndicate uses ancient Chinese number characters to refer to pages and words in a commonly known book (which was ...
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1answer
98 views

How to find the type of symmetric cipher? [closed]

How to find the type of symmetric cipher that was encrypted. I have ciphertext, plaintext, key. there is a command in openssl?
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1answer
73 views

What is the general purpose of concealment algorithms introduced in…? [closed]

What is the general purpose of concealment algorithms introduced in https://eprint.iacr.org/2003/050.pdf?
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1answer
65 views

Do I need to use HMAC in this crypto wallet backup application?

I'm building an application for securely backing up cryptocurrency private keys or 12-word backup phrases that crypto wallets use as a seed to generate private keys. For the purpose of this question, ...
4
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1answer
769 views

How can an all-zero encryption key result in plaintext ?

In the Krack-attack paper, the section 6.3 says that a vulnerability on Android devices involves installing an all-zero encryption key when the message 3 is re-sent. In his demonstration, he shows ...
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2answers
85 views

Shortest key in symmetric algorithm used only once is unsecured?

Considering a message of n bits, one ridiculously short key of 1 bit and using this cryptographic function which performs the <...
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1answer
474 views

How does Permutation and Substitution work?

I'm a little confused on how permutation and substitution works, I've been reading about S-DES and how it goes through P-Boxes and S-Boxes but what goes on inside P or S in the algorithm? Are these p ...
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1answer
2k views

Why do we use multiple rounds of encryption?

I understand that DES and AES use multiple rounds of encryption to secure the cipher text output, what is the real reason this is carried out? Is there a certain point performing multiple rounds ...
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2answers
260 views

Is it enough to encrypt then sign when using symmetric-key encryption?

I'm doing some tests in Java, encrypting messages exchanged between two entities. I'm using a symmetric key to encrypt the messages. Right now I've stumbled upon a question. Is it enough to encrypt ...
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3answers
232 views

Encrypt password for oneself on paper

Assume the following: You have to encrypt a file (ZIP-file) containing import information. This file should be password-protected and you want to leave yourself the password encrypted (on paper, ...
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1answer
112 views

Why does the Gameboy Advance serial encryption include the destination byte address?

The Gameboy Advance encrypts data sent over its serial port. It assembles a random number to seed a linear congruential generator. Then, it xors this PRN, the data, a symmetric key, and the byte ...
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4answers
858 views

Can I encrypt data with multiple keys and decrypt with one? [closed]

Can I encrypt data with multiple keys and decrypt with one? To be clear, I am not saying encrypt a file, decrypt it, then encrypt it again with a different key. I want to encrypt it, then encrypt it ...
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2answers
365 views

Use of symmetric keys rather than asymmetric keys for transport security

Alice has an asymmetric key pair and it also has Bob. They want to encrypt traffic between each other. It would be simple to encrypt the traffic with their public keys, but instead they use key pairs ...
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1answer
899 views

When is public-key crypto used / when is symmetric crypto used?

I read in the book "Cryptography & Network Security" that it has almost been universally accepted that public-key cryptography is restricted to only being used for key management (Does this mean ...
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1answer
175 views

Is libsodium's `box` construct secure without additional manual padding of the plaintext before encryption?

I have read the following questions and answers: How safe are Libsodium Crypto Boxes? What can be learned from the ciphertext of LibSodium's crypto_box_detached()? However, neither of these ...
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0answers
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an asymmetric encryption scheme with multiple distinct private keys [duplicate]

Is there a asymmetric encryption scheme that allows for multiple private decryption keys? where m= plaintext message and c= cyphertext message c = Ek(m) where K is the public encryption key. and ...
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1answer
358 views

symmetric encryption with fixed size

What I basically need is a way to encrypt and decrypt symmetrically an ID which is a string. Both version of the ID will live and work in different domain and I need a way to switch domain without ...
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2answers
477 views

Why does DESX break if one removed post whitening?

DESX uses whitening to strengthen against brute force attacks. What is an attack one could use to recover DESX's pre-whitening key with only two known ciphertext/plaintext pairs, given that the ...
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1answer
237 views

Is ciphertext stealing important in relation to Blowfish?

I am writing a simple messenger (as a proof of concept not for production), and I came across Blowfish as being as being an interesting alternative to AES. As it is not meant to be an actual ...
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1answer
241 views

Crypto algorithm identification (reverse engineering)

I'm trying to identify a certain cryptographic algorithm used in a program. From examining the executable, it appears it Has 16 rounds (plus 2 "rounds" for pre/post processing) Pads the input ...
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2answers
143 views

Existence of 99% successful unbounded adversary against randomized secret key encryption scheme with short keys

It can be shown that if $E$ is a deterministic encryption with key of length $n$ and messages of length $l\geq n + 10$ then there exist two messages $m_0$, $m_1$ and a strategy for Eve so that given ...
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1answer
64 views

Best way to go about understanding proofs and cryptography in general? [closed]

Studying both symmetric and asymmetric cryptography and having the hardest time doing so. I wanted to ask what is the best way to go about learning proofs? I don't have a strong mathematical ...
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1answer
237 views

Is the nonce in GCM mode used as key for HMAC? And how to send it?

So, my believe is that, in some way, GCM mode or any other authenticated encryption mode is useful to provide encryption and integrity for the ciphertext altogether instead of having to handle the ...
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2answers
519 views

AES-GCM for Securing Bluetooth Low Energy Application

I have a task at hand on designing security on Bluetooth Low Energy application layer. The system is created so that only smartphones with symmetric key (long term) could communicate and control my ...
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1answer
67 views

Pad ciphertext with arbitrary number of bits

I have a symmetric-key encryption scheme. I think the output from this scheme (MAC + IV + CBC ciphertext) should already be practically indistinguishable from random, but I would like to pad the ...
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1answer
434 views

AES-encrypted 128-bit null block: lookup table?

Let's say a 1MB file has many many consecutive null-bytes 128-bit blocks. Then, as AES works with blocks, the encrypted file will also have recurrent 128-bit-long patterns of ...
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1answer
79 views

Increasing rounds in DES, increases or decreases the security?

I was wondering whether in DES, if we used more than 16 rounds, the security of the message was increased or actually decreased? (disregarding the decreased speed ...
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3answers
2k views

What's the difference between block ciphers and symmetric-key encryption?

Both block ciphers and symmetric-key encryption use a secret key to transform plaintext into ciphertext, and do so in a reversible manner. Are they the same? Or does symmetric-key encryption also ...
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1answer
248 views

Searchable Symmetric Encryption VS Deterministic encryption?

I am a beginner learning about encryption. The Searchable Symmetric Encryption is better than Deterministic encryption? When I say better I mean smaller leakage.
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4answers
293 views

Transferring Encrypted One-time pad over the internet

I was working with one-time pad, and as I understand , for one time pad to be 100% secure a key shouldn't be repeated. So assuming Alice and Bob have to exchange messages over the network secured over ...
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2answers
191 views

Which element produces randomness in symmetric block ciphers encryption

Talking about symmetric encryption, I have 3 elements which I keep trying to puzzle together: IV, encryption mode, and padding. My question really is which of these elements makes the ciphertext be ...