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Questions tagged [encryption]

Encryption is the process of transforming plaintext using a cipher into ciphertext to make it unreadable to anyone except those possessing the key. Decryption is the process of transforming that ciphertext back into plaintext, using the key.

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Is this problem still as hard as discrete logarithm (modified ElGamal)?

I am trying to find a vulnerability or proof for the following problem: ElGamal part. Given $g\in\mathbb Z_p$ where $g$ generates $\mathbb Z_p^\star$, select randomly $k\in\mathbb Z_p$ and calculate ...
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Differences between hash- and encryption algorithms?

There is a lot of confusion between hash- and encryption algorithms; I would like to understand: When do we use a hash algorithm and when do we use an encryption algorithm (a cipher)? How difficult ...
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How can process algebra help to design security protocols?

Would you please tell me how process algebra could help me to design security protocols? More specifically, can I use it for proving the security of protocols? Is process algebra used for any ...
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Need help decyphering message [closed]

THEIR DIFFERENCE WILL REMAIN, LONG AFTER THEY ARE DEAD Dear Friend, IV IV 12 8 14 - 19 14 18 9 13 IV I C C 9 17 IV 17 12 IV 8 14 IV 7 F 14 IV 7 19 D IV 12 15 F 19 E IV 8 17 IV 7 12 15 F 19 13 17 9 E ...
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What is Quantum Cryptography?

When it comes to exchanging secure information over an insecure channel, this approach is considered. It all depends on the nature of photons in which third polarization is focused. It can easily be ...
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655 views

Encrypted String length in c#

I am using AES encryption in my application. I used 3 types of encryption AES-128,AES-192, AES-256 keysize. When I encrypt with different keysize(128 or 192 or 256) with the same text, the encrypted ...
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474 views

The role of Shift Register Cascades in Cryptography?

Clearly, there are stages when binary bits are needed and this can be done with the help of Linear Feedback Shift Registers. Registers are required to be connected in such a manner that one register ...
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how to compute Bit Independent Criteria on a 4-bit S-box?

The idea of Bit Independence Criterion (BIC ) was introduced by Webster and Tavares . For a given set of avalanche vectors generated by complementing a single plaintext bit, all avalanche variables ...
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Cannot understand Block Cipher example

I learned modern block cipher and saw this example. How many padding bits must be added to a message of 100 characters if 8-bit ASCII is used for encoding and the block cipher accepts blocks of ...
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Can quantum computers put computer security in jeopardy?

There are many articles about quantum computers describing how powerful they are in computing and that they can solve very complicated equations in a short time. One of the biggest security measures ...
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28 views

Need literature or link to family of cryptographic invertible polynomials which has distribution similar to inverted bell curve

Please help me identify a family of polynomials P(x,k) with the following properties: $x\in Z_{2^n} $ $\forall k, \forall p_k\in P,\ \exists\ p_k^{-1} |\ p_k^{-1}(...
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Where should I start to learn cryptography? [duplicate]

I want to learn cryptography. I just wanted to ask people who experienced about the field that where should I start? Any recommendation would be something for me. Thank you in advance.
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Is function Deterministic or Probabilistic in the malicious security definition?

As you see, according to the attached definitions from "Efficient Secure Two-Party Protocols", the definition of the security in the semi-honest world has two cases for $f=(f_1,f_2)$.(deterministic ...
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1answer
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autokey script gone wrong!

I tried to make a script to encode a txt with the autokey cipher. From my poor understanding of the cipher I created another cipher which has nothing to do with autokey: first I encoded a txt with a ...
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How can I get the message which was encrypted before (when decrypting a product cipher) ?

I want to make a product cipher containing s box and p box. where message $m = \{m_1, m_2, m_3, m_4\}$ where $m_i \in \{0, 1, \dots 25\}$ for $i=1,2,3,4$. p-box: $P(x_1, x_2, x_3, x_4) = (x_1, x_3, ...
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understanding the block bits for DES

I'm trying to understand cryptographic protocols, and I've started with the DES algorithm. DES specs: it uses 64 bits for the plaintext, 56 bits for the key, with a result of the same 64 bits of ...
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Does it make sense to have long SSH Key with shorter Passphrase?

If we encrypt our data with a longer SSH key which is protected by a shorter passphrase (with a decent entropy), then the limiting factor is entropy of the passphrase. So why do we use a longer key at ...
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41 views

IV transmission from Transmitter to Receiver side in CTR mode for every call

I am using block cipher mode (CTR Mode) for the transmission of voice data. Need to know, how can I transfer the same IV at the decryption side (for every call) as the IV for the same packets on ...
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what is the impact of smaller bit size sbox

There are multiple S-boxes type, as DES uses 4 bit S-box and AES uses 8 bit S-box. I want to know how this effect the security?? If we use 4 bit or 8 bit. apart from the DC attack. Both provides ...
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what can attackers do between two end hosts

I have one question that I couldn't come up with a nice solution. So let's have this analogy, I have a box full of money and I want to deliver to this my friend. Here if we think of a potential ...
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Calculate all possible keys for AES 128 encryption to exploit hardware encryption

Some background: I am using the MicroChip ATAES132a for hardware encryption/decryption. The ATAES132a is very configurable and can be misconfigured in such a way that the encryption/decryption will be ...
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How is a ciphertext encrypted using random numbers decrypted using a symmetric key algorithm

We use true random number generators as a source of keys for encryption. What I can not wrap my head around is: How is this cipher text decrypted in case of symmetric key algorithm as we need the same ...
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How secure is a 128 bit ideal substitution cipher

A 128 bit ideal substitution block cipher substitutes 128 bit blocks with randomly assigned 128 bit blocks using a key table. How secure is this type of algorithm? Is this practical? Thanks!
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VeraCrypt a weak point [closed]

Biggest flaw in VeraCrypt(or other Encryption programs) is Hash Algorithm. VeraCrypt hashes (SHA,Whirlpool,Streebog) it is the only point where can break an encrypted disk. Because break algorithm (...
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101 views

Hardware, Handheld Password Manager

I am currently working on a hardware project that will utilize the native USB and keyboard emulation capabilities of the Teensy device. Essentially, the user will store an encrypted password database ...
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1answer
304 views

Use AES in CTR mode with pycrypto

The doc of pycrypto gives an example of using AES in CTR mode: ...
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1answer
47 views

Encrypting the relationship between two database tables

I'm not a cryptography expert myself, and know enough to know that I shouldn't design my own crypto schemes, so I thought I'd seek advice here. In an application, let's say we have two database ...
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135 views

“Power of one” as input to functions of a cryptosystem

What does $1^\lambda$ mean when you pass it as a parameter to the functions of a cryptosystem. The cryptosystem in question is this and a picture reference is this. I have been told it signifies the ...
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Using a blockchain for secure communication

I've recently heard of the idea of using a blockchain for secure communication. No details were given so it's a little hard for me to say that it can't be done. But as far as I know: Secure ...
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2answers
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How to beat a substitution cipher when adding a pseudo-random number stream?

From view-source:https://web.archive.org/web/19990224060310if_/http://www.cl.cam.ac.uk:80/PGP/pgpdoc1/pgpdoc1_29.html: When I was in college in the early ...
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Turn a homomorphic encryption scheme into one that doesn't have the homomorphic property

Homomorphic encryption is a form of encryption that allows computation on cipher-texts, generating an encrypted result which, when decrypted, matches the result of the operations as if they had been ...
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How can one turn a malleable encryption to not malleable

An encryption algorithm is "malleable" if it is possible to transform a ciphertext into another ciphertext which decrypts to a related plaintext. That is, given an encryption of a plaintext m, it is ...
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Is this problem same as discrete logarithm?

Given $g,h\in\mathbb Z_p$ where $g$ generates $\mathbb Z_p^\star$ Discrete logarithm problem is to find $z$ such that $g^z\equiv h\bmod p$ holds. Take the problem given $g,g',h$ where $g^z\equiv h\...
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178 views

When do I need to use hybrid cryptography?

I need to provide confidentiality for a protocol. The protocol message size is between 100 bytes to 500 bytes. Do I need to use asymmetric encryption or hybrid cryptography?
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Perfect secrecy theorem

Let $E = (E,D)$ be a Shannon cipher defined over $(K,M, C)$. Consider a probabilistic experiment in which $k$ is a random variable uniformly distributed over $K$. Then $E$ is perfectly secure if and ...
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Which cipher text is easiest to guess the plaintext?

I know that there are approximately 2^88 diff erent permutations of 26 characters. The stream cipher A5/1, which generates a binary keystream using three irregularly clocked LFSR, and has a 64-bit key....
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Practical perfect security in bitwise XOR vs integer addition/subtraction cipher

XOR already provides perfect security in theory but it's hard to apply it in practice due to strict requirements. I was thinking about whether simple addition/subtraction in integer format would not ...
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Example of an attack on a message exchange which uses the homomorphic property

Can someone give me an example of an attack on a message exchange using this encryption scheme, that uses the homomorphic property? In my opinion, Existential forgery under directed message attack ...
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Triple Data Encryption Standard [closed]

Based on this, it looks like something slightly wrong. What would need to be adjusted at the transmitter side to allow the receiver to decrypt the message/data?
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How to provide partial confidentiality and full integrity for a protocol message?

I want to provide confidentiality and integrity for a protocol. I don't want to encrypt the entire protocol message. I do not want to encrypt the header and timestamp of the protocol message, but I ...
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1answer
62 views

How do i manage encryption keys with a cloud provider?

I would like to provision services from a Software as a Service (SaaS) provider. This is multitenant environment (multiple companies will be using a single instance of the application, with a single ...
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1answer
56 views

Trivial Broadcast Encryption Scheme for video conferencing how well does it handle users joining or leaving a call?

Consider the trivial Broadcast Encryption Scheme for video conferencing, where each user shares a long-lived key with the broadcaster, and the session key used to encrypt a multicast message (or ...
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80 views

Good Diffie Hellman Encryption Method

I've just made my own implementation of Diffie Hellman in nodejs (its for a project of mine). However the shared keys are integers, I want to use those integers as a key to encrypt data. This is an ...
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238 views

Encryption using static AES256 symmetric key vs ephemeral session key

For a hackathon I am designing an information exchange system for healthcare. Healthcare data is stored on unsecured systems. I want to assure confidentiality, integrity and authenticity of this data ...
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1answer
128 views

Avoid decrypting every password in a password manager

The Setup I'm making a password manager for fun. It stores a random encryption key, encrypted with a key derived from the master password, and then it stores the data, which is a list of (site, ...
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1answer
67 views

Proving impossibility for a stronger primitive

I have a primitive $A$ which is impossible to prove under some hardness assumption in a black-box way. Now, if another primitive $B$ is stronger than $A$ - in other words $B$ implies $A$ - will it ...
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2answers
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Ring Signatures: Why is the combination function easy to solve?

I'm reading Rivest's How To Leak A Secret and am on the part where they describe their signature scheme ("Generating a ring signature"). Why is computing $C_{k, v}(y_1, ..., y_r) = v$ easy? The ...
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Concept of hashing a group of data and validating if a value exists within the group

When learning about cryptography and hashing, I remember seeing a concept where you could hash a number of values (ID's for example) and then validate against the hash, not storing the original IDs. ...
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Is it safe to use a timestamp to build a nonce?

I'm writing an application, which can be used on multiple clients, and share data on a server. To make sure the data never leaves the clients unencrypted, the application should offer encryption with ...
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202 views

Append text to file without decrypting & encrypting again

Is it possible to add a line to a file which is encrypted symmetrically or asymmetrically (private key refers to readkey below, public key refers to append key then) without decrypting it? I was ...