Questions tagged [symmetric]

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

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OTP stream cipher

I am new to cryptography so there is one thing which is bothering me. I hope you kindly help me to understand. Let's imagine an attacker harvest plaintext as well as ciphertext in OTP One Time Pad. I ...
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Is a message digest useful with symmetric encryption to check for integrity?

I have some confusion that concerns the message digest. I know that the message digest is the real message hashed with function and we use it to verify the integrity of the message. I understand the ...
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Property that prevents determining key from ciphertext and plaintext

What is the property (if it is not Forward Secrecy) that prevents (good) symmetrical encryption algorithms from being vulnerable to an attack vector that requires only decrypted data, and the ...
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128 views

Whats the most secure way to encrypt a string without the use of a computer? [duplicate]

I want to decrease attack surface by preventing the plaintext string or encryption key from ever being typed or otherwise entered into a computer. Ideally the decryption key would be something that ...
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1answer
3k views

AES key expansion for 192-bit

In AES-192 key expansion there are 12 rounds and 52 keys. I am not sure why 52 keys are derived since each block consist of 4 rows and 6 columns (192 bit keys). So if the block is 4 x 4 then we ...
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Java - AES with 20 byte packet

I have 20 bytes of data that I need to encrypt and send to a bluetooth node. The main issue being that the receiving node only accepts 20 byte packets. Further, I cannot send multiple packets, one ...
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1answer
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What Is The Weakest Possible Encryption Algorithm [closed]

I've been creating a Capture The Flag site and for one of the challenges I wanted you to have to break an encryption algorithm. Granted I want it to be a weak one, so I want the weakest out there. One ...
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1answer
302 views

Is this MAC-then-encrypt scheme secure?

I have the following requirements: 64 bits (8 bytes) of data ($D$) that requires confidentiality and integrity; the data itself is a nonce, never need to authenticate/encrypt the same value twice (e....
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Why is Symmetric encryption classed as Private Key?

I am going for my ethical hacking exam soon and I still can't get my head around why symmetric key encryption is classed as "Private/Secret Key encryption" when symmetric encryption uses the same key ...
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248 views

Suitable Symmetric Algorithm for Encryption

Please, I would like to encrypt word not more than 5 letters such as (GO, HI, APPLE, EYES) and my key length just (40 bits only), please I am looking for a suitable symmetric algorithm that it can be ...
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1answer
593 views

Simple secret key encryption with PyNaCl [closed]

I am playing around with PyNaCl to get a bit into cryptography atm. Now I wrote two scripts to encrypt a file with a secret key and then decrypt it again using that key. The encryption part works ...
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1answer
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compact hardware implementation of inversion based 8-bit s-boxes

$\DeclareMathOperator{\GF}{GF}$ I cannot figure out how should I determine the matrix for transmission over $\GF(2^8)$ to $\GF(((2^2)^2)^2)$ in compact hardware implementation of inversion based 8-bit ...
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Using symmetric-key cryptography

A group of 30 people who wish to establish pair-wise secure communications using symmetric-key cryptography. How many KEYS need to be exchanged in total?
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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 ...
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1answer
171 views

Does key-length recommendation provided by NIST consider quantum computer?

Here we can see the suggested key-length by NIST in a few decades: https://www.keylength.com/en/4/#Biblio10 Does this consider quantum-computer?
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238 views

For a typical n-bit symmetric key, how many keys would be considered too weak to use?

I understand that all zeros or all ones would be weak for any cipher. And certain ciphers, e.g. DES, have a list of weak keys. But I assume that there would many 'patterns' that would be detected (if ...
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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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151 views

Indistinguishability in the presence of an eavesdropper attack scenario

The property of Indistinguishability in the presence of an eavesdropper as described in the following experiment: (tract from: Introduction to Modern Cryptography) It must be interpreted as a ...
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Difficulty of finding partially matching ciphertexts for a given plaintext when encrypted with two different keys

I'm trying to find a simple, practical proof-of-work scheme based purely on encryption (due to wide availability of optimized, hardware accelerated AES execution on most platforms, including modern ...
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533 views

How to recognize Authenticated Encryption with Associated Data ciphersuites

I have some doubts regarding AEAD ciphersuites and I need some clarification. In the following ciphersuites list: ...
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Password derived hash to encrypt known plaintext as password check

The title sounds way too adventurous for what it actually is. I am currently building a system which features some encryption. There is already a system in place, which is built after that scheme if ...
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1answer
131 views

Getting the Encryption Function From the Decryption Function + Decryption Key + Encrypted Item

Is it mathematically possible to always be able to get the encryption algorithm used to encrypt a certain item (file, number, text, ...etc.) by knowing the decryption algorithm that will be used to ...
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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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How much faster in symmetric cryptography compared to asymmetric cryptography? [closed]

I know that symmetric cryptography is faster than asymmetric, but on average how much faster would it be if you were encrypting and decrypting a 2MB file?
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Decrypting partial message.

I'm wondering whether such interesting symmetric-key encryption exists or not (from theoretical perspective): We encrypt a vector of messages $(m_1,m_2,\cdots,m_\ell)$ using the symmetric key $K$ to ...
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1answer
355 views

What is a differential trail?

From what I could find it relates input differences to output differences usually across multiple rounds. But is it the entire probability distribution over all output differences for one input ...
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Are there any deterministic multi-block encryption constructions that have an avalanche effect going both ways?

For common multi-block encryption schemes (CBC, CTR, CFB, stream ciphers, etc), if they are forced to be deterministic, a change in the plaintext will change only the current block and maybe future ...
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Signing an exchanged symmetric key that is asymmetrically encrypted

Consider the following implementation: Bob wants to communicate long-term with his team over an unsecured channel. Bob and all members of the team generate individual public/private keypairs (ex. ...
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Fast Symmetric Encryption Algorithms: My Options

Basically, the question above... I'm trying to implement encryption on the server, and I have another webserver that I can share a secret key with via TLS/SSL/HTTPS, so I do not really need ...
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NIST's Recommendations for Protection of CLASSIFIED Data?

In NIST Recommendation for Key Management Part 1 Rev 4, It states in Section 1.Intro This NIST Recommendation applies to U.S. government agencies using cryptography for the protection of their ...
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Encrypted messaging web app design

I’m implementing an encrypted messaging web app using JS. When composing a message, the user is provided with the public key of the recipients. A body field is also rendered for every recipient. After ...
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1answer
712 views

Is it possible to derive an asymmetric algorithm from a symmetric one?

Given the advancements in quantum computing, there's a lot of incentive to move away from the usual asymmetric cryptography. Is there a way to turn a symmetric algorithm (e.g. AES) into an asymmetric ...
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What is the difference between a Stream cipher and a Symmetric Encryption algorithm?

According to the Tag definitions: Stream Cipher: A stream cipher is an encryption algorithm which encrypts arbitrary length plaintext, using a key. Some stream ciphers generate a keystream from only ...
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Why do we need to go through multiple cycles in block cipher

According to Computer Networking: a top down approach, Chapter 8 (6th edition), block ciphers involves breaking the input message into blocks of size k, where generally k = 64. However since k = 64 ...
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Bit slice format of 4x4 s-boxes?

I have studied bit-sliced implementation in SERPENT block cipher and I need to use this technique to implement some 4x4 s-boxes. I couldn't find any procedure to obtain bit-sliced format in any paper ...
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59 views

Restricting symmetric key usage

I have a system where some clients communicate with a server. every client has its own name and role and some other parameters that sends these info to the server in every message and the server uses ...
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What is the correct way to implement PBKDF2 + AES CBC + HMAC?

I've been doing a lot of reading on the proper way to implement AES CBC mode with HMAC authentication. I've seen many explanations, however, I've had a hard time finding an actual real example (with ...
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Explain Garbled circuit having function and single input?

I came across below Image of garbled circuit and want to know what exactly is garbled circuit and if we consider two party computation then how can we differentiate between f and x as Alice and Bob's ...
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How to create and send a symmetric key using GPG

I want to communicate with a friend (he lives in another country so we can't exchange fingerprints or keys physically, I could post him a USB disk but I'm sure I can do it through the web). I'm ...
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Should I use independent symmetric keys for each client should I use keys derived from a master key?

I have several clients that I communicate with from a central location. All connections are encrypted using static symmetric keys that are hard-coded in each client config file. I use a different key ...
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1answer
99 views

Yahalom Protocol

Here is the Yahalom Protocol: https://en.wikipedia.org/wiki/Yahalom_(protocol) I don't understand how Alice forms the 2 messages sent to Bob in the fourth step? Where does the data come from? For ...
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How to break homophonic substitutions and nomenclators with too many symbols?

Early attempts to thwart frequency analysis attacks on ciphers involved using homophonic substitutions, ie. some letters map to more than one ciphertext symbol. The earliest known example of this, ...
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463 views

What kind of symmetric-key algorithm to use with Diffie-Hellman?

Let's assume we use DH with a cyclic group modulo p. As I know safe length of p must be at least 1024 bits. That means that ...
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Rijndael - is there some difference in resistance between counter in generator input and in IV?

I am thinking about Rijndael implementation in order to store tokens (cannot be hashed) - one token for one user. And finally I get stuck with key/IV generation problem :( The questions are: 1) Is ...
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How would Private-key Cryptography be if we use quadratic polynomials as OWF's?

I am aware that one-way functions (OWF's) are the core of many of the primitives in symmetric crypto, in the sense that many cryptographic primitives in the private-key setting can be constructed from ...
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zero knowledge messaging implementation

I understand that messages are encrypted using a symmetric algorithm such as AES, and the symmetric key is encrypted using an asymmetric algorithm such as RSA. In my particular implementation, the ...
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272 views

Asymmetric vs symmetric encryption

I am a beginner learning about encryption and I would like to ask a few questions, hoping this is the right place to ask, so please bear with me. We have Alice and multiple clones of Bob. Only Alice ...
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Is it necessary for the Rijndael polynomial to be primitive?

I am working on selecting a S-box for my Cipher (Similar to AES). I found out there are 30 irreducible polynomials and over 16 primitive polynomials of degree 8. Is it necessary to choose a primitive ...
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Are there deterministic private-key encryption schemes that are CPA-secure?

I'm assuming there can't be such schemes because CPA-security is equivalent to CPA-security for multiple encryptions, and an adversary can distinguish between $(\mathsf{Enc}_k(m_0),\mathsf{Enc}_k(m_0))...
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Is the risk of a collision for OCB mode mitigated by upping the block size of the cipher?

A paper published by Niels Furguson Collision attacks on OCB indicates that processing large amounts of data (somewhere on the order of $2^{32}$ 128 bit blocks) with a single encryption operation (...