Questions tagged [symmetric]

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

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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
721 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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0answers
251 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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1answer
63 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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3k views

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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1answer
103 views

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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123 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
100 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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1answer
465 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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0answers
251 views

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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1answer
172 views

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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275 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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1answer
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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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1answer
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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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2answers
537 views

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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1answer
217 views

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
115 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
290 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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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
666 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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583 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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338 views

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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1answer
112 views

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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2answers
999 views

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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3answers
601 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
128 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
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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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1answer
474 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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2answers
668 views

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 ...
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1answer
67 views

Special equivalent key in symmetric encryption

Let $k$ and $k'$ be two keys of symmetric encryption such that for some $m$ we have $ Enc_k(m)=Enc_{k'}(m)$. Is it possible to exist a plain text $m'$ such that $Enc_k(m') \neq Enc_{k'}(m')$. In fact,...
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1answer
128 views

Create a bijective and invertible table that are depending on the cipher key

I'm creating my own symmetric-key algorithm that in many ways are similar to DES. My key is 16 bits long and is random generated, I will encrypt blocks of 16 bit strings that are split into two 8 bit ...
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1answer
271 views

Value of new symmetric key algorithm

When I was in grad school, I invented (discovered?) a new PRNG algorithm. This algorithm has an infinite period length (given infinite memory). This in itself cannot be new, because all you need to ...
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2answers
926 views

Is there a difference between private key cryptography and symmetric encryption?

I have often seen these terms being used interchangably, but is that correct? Are there Private Key Algorithms that do not use Symmetric Encryption?
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1answer
316 views

What are the costs of generating master key for symmetric ciphers?

I recently read that generating large master keys for symmetric ciphers is very expensive. But what exactly do they cost? Any references would be much appreciated. I have checked NIST but actual costs ...
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3k views

Diffie-Hellman “handshake” vs RSA “handshake”

I have a question about exchanging symmetric keys. I have read something about the Diffie-Hellman algorithm, where two parties generate the shared key independently, sharing only some parts of it ...
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1answer
132 views

Negative negligible functions

If f(n) is a negligible function, is -f(n) also negligible by definition? Since $$f(n) < \frac{1}{p(n)}$$ for all positive polynomials $p(n)$ and for some integer N such that $n > N$ Thus $$-f(...
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Isn't AES-NI useless because now the key length need to be longer?

AES-NI speeds up both encryption and decryption. The encryption is as secure as the time needed to brute force the decryption. Doesn't it mean that the application developers will just need to ...
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1answer
410 views

How does Kerckhoffs's principle apply to Adversarial Neural Cryptography?

Martın Abadi and David G. Andersen recently published a paper on arxiv titled: "LEARNING TO PROTECT COMMUNICATIONS WITH ADVERSARIAL NEURAL CRYPTOGRAPHY" (https://arxiv.org/pdf/1610.06918v1.pdf). I ...
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1answer
142 views

Determining the encryption method [closed]

I am trying to reverse engineer a program that encrypts a file with a password. So far i figured out that the start of the file is always the string "DecryptOK" encrypted with the password of course. ...
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Algebraic Attacks against ARX

I have not seen much about algebraic attacks against ARX ciphers. How would ARX ciphers compare in algebraic security to AES or Present or Simon?
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2k views

How can I calculate the avalanche effect in symmetric algorithms?

I am working with symmetric algorithms in Java with javax.crypo and Bouncy Castle libraries and I need to calculate the avalanche effect of different symmetric algorithms such as DES, 3DES, Blowfish ...
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3answers
3k views

Public key encryption and message integrity

Let's say I want to send an encrypted email thus I encrypt it with the receiver's public key, so that the receiver uses its private key to decrypt it. If someone tampers with the message in between ...
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1answer
326 views

What is the difference between “Linkable” and “Traceable” Ring Signatures?

In particular, both papers on Traceable Ring Signatures and Linkable Ring Signatures propose they are fit for the creation of ballots. The Wikipedia Article on Ring Signatures, though, suggests ...