Questions tagged [symmetric]

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

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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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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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3answers
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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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2answers
508 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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214 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
110 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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257 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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255 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
610 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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556 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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444 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
122 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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329 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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471 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 ...
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1answer
66 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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123 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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270 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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914 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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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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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
118 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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408 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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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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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
317 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 ...
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1answer
737 views

Evaluatung Shadowsocks Crypto strength

I recently asked a question on security.stackexchange.com about whether Shadowsocks is MITM-able and the answer was helpful yet I would like to understand symmetric crypto / the crypto used in ...
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923 views

Encrypting 256 bit AES keys with AES ECB?

What are the pros/cons of using AES ECB mode to encrypt encryption keys (data encryption keys or DEKs)? Aware of the significant weaknesses when it come to encrypting low-entropy data that's greater ...
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2answers
392 views

How effective is Serpent-256 in CTR mode?

I downloaded a compression program known as PeaZip which offers encryption and 2-way authentication also. PeaZip has an option to encrypt compressed file with variety of ciphers and one of them is ...
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1answer
193 views

Same-length plaintext results in predictable ciphertext. Can a substitution cipher avoid this issue?

I started with a basic mixed-monoalphabetic substitution cipher. To work against predictable ciphertext generation, I introduced a modulo in my cipher whose purpose is to scramble the substitution in ...
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1answer
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TRNG and Stream ciphers

How do phenomena such as mouse movement or thermal noise are exploited as TRNG within a symmetric crypto-system (e.g: Stream cipher)? I will really appreciate if anyone could provide me with a ...
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1answer
59 views

Symmetric key pair on app and low power device

I have a microcontroller based device that is controlled by a smartphone app. To make the communication between the two secure, I'm encrypting the communication between the two using AES. However, ...
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1answer
99 views

“open-key model” attacks, why would one be concerned?

In a paper on a Feistel network, I found the line we have made no effort to guard against attacks in the open-key model and then I found this paper at iarc.org on the subject. I found only a ...
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1answer
301 views

Homomorphic encryption or double symmetric encryption?

I am new to Homomorphic Encryption. The scenario is that the encrypted data will be sent from Alice to a trusted cloud machine for computing operations and then sent to Bob. Can HE (e.g. NTRU) be ...
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1answer
352 views

Fast encryption for Medical System?

For part of my bachelor thesis (which will be involved in a commercial product), I need to build a cryptosystem that will be used to encrypt and decrypt continuous medical data that is transmitted ...
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1answer
128 views

How secure is encrypting with self-hash [duplicate]

I don't have much knowledge about cryptography beyond using libraries for it. So just wanted to understand if the following two cases differ sufficiently in security or is it just psychological: Say ...
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3answers
200 views

DIY message level security?

This might be in danger of being too elementary a question for this community but I'm hoping for expert help: Assuming that TLS is not enough to protect messages transmitted between a client and a ...
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1answer
1k views

How to do statistical analysis on encrypted / anonimized data

Let's imagine Alice wants to send Bob a table with 2 columns: ...
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Is anyone using Half-Bit encryption? What is it used for now?

Long ago I learned about an encryption scheme which uses a random mask of bits which were "half on". I don't recall all the details, but basically, if a mask bit was a one, the input bit was passed ...
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To utilize asymmetric cryptography in symmetric manner - demand-of-security-definition?

Cryptography can largely be divided into two classes: asymmetric and symmetric. Like homomorphic encryption now greatly restricted in the asymmetric cryptography, the difference of asymmetric and ...