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Questions tagged [symmetric]

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

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Polyalphabetic rotation cipher over digits [on hold]

what is the keyspace of a poly-alphabetic rotation cipher over digits, with a repeated key-length of 2, in which no digits can encrypt to itself? Why is the answer 72?
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Two possible plaintext's using OTP decryption

I am using this cipher-text c = 04 10 12 00 01 08 67 0A 19 65 0F 03 0A 00 with two possible keys ...
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4answers
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Why use symmetric encryption with Public Key?

A. From what I heard (and I am beginner at a security/cryptography), if you have a payload that is very large, asymmetric is a no-go. B. Also, if you do have secret symmetric (e.g. AES) keys, you ...
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Post Quantum Symmetric Cryptography

So I am looking for the most secure method of symmetric key cryptography for long term messaging use between two users. I have heard that most symmetric key algorithms are not absolutely compromised ...
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31 views

Commitment based on authencticated encryption

Let $(E,D)$ be the encryption/decryption of an authenticated encryption scheme. Consider the following commitment scheme. Generate a random key $k$. Commit to $m$ by sending $c=E_k(m)$. Reveal $m$ by ...
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Is it possible to execute elliptic curve encryption on small sensor-tags CC2650?

I am working on a project wherein ECC needs to be implemented on small devices, namely, CC2650 sensor-tags for authentication. The ECC implementation should be on Contiki OS. I have read some articles ...
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Encrypting multiple small messages with a single reused symmetric key

What is a good way of doing this? Practical and Secure. This is for a browser environment. For example, let's say there are a few 100 independent messages of about 100 characters each that you want ...
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Lightweight provably secure design [closed]

Is it possible to device lightweight (i.e. without asymmetric crypto and PKI; and without third party Trent) provably secure (in the exact security sense) scheme? Were there any attempts? Is it ...
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Security of key bits under indistinguishability for randomized encryption

My question is about symmetric randomized encryption. Let c=E(k,m,r) be a randomized block encryption function where r denotes a random input chosen for each message block m. k and c denote the ...
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1answer
65 views

How is Shamir's Secret Sharing better than this simple 2-password technique?

I'm looking for a solution to protect a message, such that both password1 (usually given to trusted person #1) and password2 (...
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1answer
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Are there any other highly trusted and secure symmetric encryption algorithms besides AES?

AES is the gold standard for symmetric encryption. It is highly trusted and highly secure. Do any other symmetric ciphers - besides OTP - come close to AES's usability, security, trust-ability?
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Are there any symmetric Partial Homomorphic Encryption Schemes?

Note that I am asking specifically for Partial Homomorphic Encryption (PHE) schemes and not Somewhat Homomorphic Encryption (SHE) schemes. I believe there are several SHE schemes that are symmetric ...
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1answer
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Is it possible to narrow down the possible keys used for AES CBC encryption, knowing a given plaintext and its ciphertext, where IV=0? [duplicate]

I'm brute forcing a ciphertext with a given dictionary to figure out which key was used. However, it's been hinted at that there is a way to narrow down the dictionary to a smaller subset of ...
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Is there any existing cipher capable of scaling from a 1 bit key up to a one-time-pad?

We have ciphers that handle small amounts of entropy, such as a 256 bit key for AES; and we have one time pads for enciphering 1:1 entropy, such as a 1GB key for a 1GB file if you could ever harvest ...
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Difference between “ECDH with cofactor key” and “ECDH without cofactor key”?

I need to use “ECDH with a cofactor key” for generating symmetric key. I have a fair idea on how ECDH works, but I don’t understand the cofactor part. What is the difference between ”ECDH with a co-...
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OTP stream cipher

I am new to cryptography, and there is one thing that is bothering me. I hope you can kindly help me to understand. Let's imagine an attacker harvests the plaintext as well the ciphertext from a ...
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4answers
898 views

Why do one-time pads not provide message authentication?

It is often said that one-time pads do not provide message authentication. But, if you and I have a one-time symmetric key, and I send you a message, and it is not complete gibberish, is that itself ...
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1answer
129 views

How does the key agreement process take place in Virgil E3Kit SDK for end to end encryption?

I'm using Virgil E3Kit SDK to implement end-to-end encryption in my App. Their E3Kit SDK is very effective and not too hard to understand, but I still don't understand how does the key agreement ...
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Are CFB and OFB really meant for streaming?

CFB, OFB and other modes are meant for streaming and don't require padding. Are there still limitations such as the text needs to be greater than key length?
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Is it possible to identify a Serpent encryption key in memory?

It has been shown that AES keys that are in use can be identified in memory. This identification relies on discovering expected round keys in memory that are contained within the key schedule. My ...
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How can we reason about the cryptographic capabilities of code-breaking agencies like the NSA or GCHQ?

I have read in Applied Cryptography that the NSA is the largest hardware buyer and the largest mathematician employer in the world. How can we reason about the symmetric ciphers cryptanalysis ...
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1answer
578 views

How to build disk encryption system using forward permutations like Gimli?

First of all, this is purely a thought experiment. The width of Gimli isn't even a power of two (384 bits), and secondary storage bus speeds aren't even worth using a high performance permutation like ...
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NIST HMAC Test vectors

I am searching test vectors of the HMAC-SHA256 primitive to verify the correctness of an implementation. Without hesitation I go on the NIST website to see what they offer. While reading the ...
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Extracting RC4 and 3DES keys from system memory

I have read papers [1], [2] that have presented techniques on extracting symmetric encryption keys from memory during the process of encryption. There are tools [3] that can extract AES keys from ...
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1answer
66 views

How does gpg know what cipher algorithm is needed for decryption?

I am using gpg to make encrypt a tar.gz. My first try uses --verbose --symmetric and then the decryption is done with ...
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1answer
89 views

Key derivation for AES-GCM using HKDF?

I have a system comprising N >1000 nodes. At each node I would like to use HKDF to derive a unique 256-bit key, Kn (for the nth node), from a pre-shared master key, K0, and a locally-generated random ...
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1answer
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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 $c$ $c = \text{Encrypt}(m, d) = \text{Encrypt}(d, d)$ is the computational cost to brute force $...
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statistical distance in symmetric-key encryption

Prove that for any symmetric-key encrytion scheme $\Pi=(Gen, Enc, Dec)$ with message space $M$ and key space $K$, there exist $m_0, m_1 \in M$ such that $\Delta(Enc(K, m_0), Enc(K, m_1))\ge 1-\frac{|K|...
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60 views

Why algorithmic symmetry is important in hardware implementation?

In AES, the encryption and decryption functions ordered in a symmetric way, I mean the same order of functions are used inside the round structure of both encryption and decryption (subbytes, ...
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1answer
45 views

Can I change the S-box and P-box in DES?

I am a newbie to crypto and just one quick question on the s-box and p-box of DES. I understood that the s-box is where the security comes from and NSA has somehow decided how it should be filled in. ...
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What exactly does s2k do in gpg

So I recently discovered the --s2k mode in gpg. Sadly it is not very well-documented. I mean, what is ...
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1answer
223 views

In GnuPG, what's the difference between --s2k-cipher-algo and --cipher-algo? [duplicate]

I want to change some encryption options while using GnuPG to encrypt a file symmetrically. 1) However, for choosing the cipher algorithm, GnuPG has two commands and I don't know which one to use. ...
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Can frequency attack be successful on Vigenère cipher?

Here is my question when learning Vigenère cipher, can we perform frequency analysis attack toward this cipher? My first impression is no, because each column of its matrix has exactly 26 English ...
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Are slide attacks effective if the primitive is sandwiched? And key schedule vs. Even-Mansour

Suppose you have a cryptographic permutation consisting of identical rounds, that makes it vulnerable to a slide attack. But if you sandwich it between two XORs of key material. Is it still vulnerable?...
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What is the intuition behind the strength of unstructured symmetric cryptography?

Consider a single round of a cryptographic permutation, what is so special about it that lacking some bits of information that either get mixed into it as a subkey or omitted at the end (sponge ...
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1answer
48 views

Is a symmetric encryption key derivable using the input and the output?

I am looking for a python library for encrypting a string with a single key. I do not want the key to derivable by knowing the input and the output. I have came to ...
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1answer
43 views

Randomly initialised global counter used to encrypt the kth message with IV = IV + k mod 2^n

The use of an increasing IV is not secure for a block cipher. That is, using a random IV for the first message then IV + 1 for the second , IV + 2 for the 3rd etc. How can I construct an attack to ...
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1answer
151 views

Single Ciphertext which can decrypt with multiple keys

Say we have a public key system where we have 2 users, Alice, and Bob each has a public and private key. We also have a publicly available server which stores a message. I want to encrypt this ...
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1answer
90 views

Reversible Decryption in Symmetric Key Algorithms

I am currently learning the Internal Working of Symmetric Key Algorithms, like DES, AES, BlowFish, IDEA just to name a few. These are all quite complex Encryption alogrithms, which requires a lot of ...
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How do I calculate key rotation schedules?

tl;dr: How do I formulaically determine key rotation schedules for different kinds of keys and use cases? The organization I'm a part of for utilizes both symmetric and public/private key encryption ...
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308 views

Does ChaCha20/Salsa have the same Bit Strength as AES for identical key sizes?

i.e. does ChaCha20 with a 128bit key, require 2^128 attempts to brute force, as with AES-128, theoretically? Ps. notwithstanding that ChaCha is a stream cipher.
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After ECDH with Curve25519, is it pointless to use anything stronger than AES128?

Is the following reasoning correct: After ECDH with Curve25519, the resulting shared secret will be an EC public key with a bit strength of 128 bits. This public key would then be hashed (let's say ...
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1answer
133 views

How strong is XooDoo vs AES?

What is Gimli, and how does XooDoo compare to symmetric ciphers such as AES or ChaCha? I am looking at this library, called charm. Interesting paper here. I also ...
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Is it possible to enhance white-box cryptography security by homomorphic encryption?

Background: Let's discussed based on published symmetric white-box crypto only, such as Chow's white-box AES. I only know basic concepts/objectives of homomorphic encryption, such as PHE and FHE. ...
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587 views

When encrypting twice with two separate keys, can a single key decrypt both steps?

Is it possible that if a plaintext is encrypted first with a key, $n_1$, and then this ciphertext is again encrypted using the same algorithm but a different key, $n_2$ that the resulting ciphertext ...
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2answers
70 views

Very short block ciphers for equally-short plaintexts

I'm trying to develop an encryption technique for encrypting short phrases (such as reversibly-anonymized names) in text. The key-generation and ciphertext-representation details are fungible, but ...
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Authenticating without sending password to the server, and store data encrypted with password derived key on server

I am trying to think of a scheme that would allow a user to authenticate to a server, whithout sending the password to the server, and to also derive a symetric key on the client (that also never gets ...
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1answer
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Are “non-mathematical” encryption algorithms comparably secure against brute force key recovery?

I recently learned about a desktop encryption application called ALKEMI, which does not use mathematical encryption according to the website, which I understand to be a misnomer, at best: The ...
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AES: Why is it a good practice to use only the first 16 bytes of a hash for encryption?

I'd like to encrypt Text with AES/CTR and a password defined by the user in java. I already checked the internet (and stackoverflow) for answers. The most used version is to hash the user password ...