Questions tagged [symmetric]

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

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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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168 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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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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2answers
342 views

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
143 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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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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3answers
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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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475 views

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
730 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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398 views

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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264 views

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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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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127 views

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
103 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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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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277 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 (...
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What impact could general quantum computing have on BCrypt?

While discussing the 72 character limit of BCrypt, the question of resilience to quantum cryptanalysis came up. A search online didn't give me much of a lead as to what research has been done in this ...
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Centralized storing of private RSA key

I working on multiuser project, where users can share data. The data that users upload to the server will be encrypted before it leaves the client with a symmetric cipher, and then the symmentric key ...
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2answers
122 views

P2P encryption - Do I need a different session key each time?

I am using AES128-CBC+HMAC for all encryption. Currently I am using the same encryption and authentication/MAC key (Both derived from a master key with HKDF). Assuming that forward secrecy is not a ...
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1answer
310 views

Why does symmetric encryption require padding?

Why does symmetric encryption require padding? Is it to avoid the attacker to learn the size of the plaintext?
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257 views

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. ...
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Reducing the output of AES to 64 bit

Is it possible to reduce the output of AES after encryption into 64 bit with the possibility of a reversible before decryption Without any error
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1answer
684 views

Encrypting decimal values with AES

I have a column in a database table called "Amount" that will store decimal values encrypted with AES. It's highly likely that the same amount will exist in multiple rows in the table and be encrypted ...
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602 views

Do I need different encryption and decryption algorithms for each key?

Is a different encryption and decryption algorithm used for every secret key, or can I use the same encryption and decryption algorithm for different keys?
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Why are multiple rounds with generated subkeys used?

In AES-128, 10 rounds are used with subkeys generated from the 128-bit key. In DES, 48-bit subkeys are generated from a 56-bit key. This seems to be common in symmetric encryption. I ask this because ...
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Given this protocol, can you find some weakness? [closed]

1) A->B A||B||{Na}Kab 2) B->A {Na+1,Nb}Kab 3) A->B {Nb+1}Kab 4) B->A {K'ab,N'b}Kab This protocol is used to refresh a symmetric session key. EDIT:...
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Encrypting small packets with low data rate

I'm trying to build my own layer of encryption on top of our bluetooth communication. We can't use bonding because of some specific features we need to support. I'm a beginner when it comes to ...
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679 views

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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1answer
133 views

Prove that (m1 ⊕ m2) = ek(m1) ⊕ ek(m2) for a 8-bit blocks i/p encryption system

I tried to work this out but I'm stuck at finding a relation between $c$ and $e(k)$: An encryption system accepts 8 bit-blocks as input. The encryption is done by XOR'ing the bits with an 8-...
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1answer
356 views

Secret key out of sha-512

This is a setup to produce a secret key for symmetrical encryption with TweetNaCl: 1) K1 consists of 32 random bytes 2) K2 consists of 32 random bytes (By "random" I mean "obtained from /dev/...
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478 views

Is this symmetric key MAC-then-encrypt auth token methodology secure?

NOTE: This question originally conflated a "digital signature" and a "MAC", which I've since learned are not the same thing. Any references (in the answer or any comments) to a "signature" should be ...
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How to properly AES encrypt a string, deriving the key from the same string?

Let's say someone has a list of names, e.g.: 'Batman' 'Batman' 'Super Man' I am auditing this list, but I'm not allowed full access to all names. So they must be ...