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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How is an epsilon of 1/1000 non-negligible?

Lately I've been studying cryptography and in the current course I'm taking we're reviewing statistical tests and how they can be used to determine if a pseudo-random generator is secure or not. ...
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simple algorithm to encrypt/decrypt a text file

I need to write a first program in one language that saves data in a text file, and write a second program in a second language to decrypt that file. The two languages in question don't include any ...
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126 views

Is it OK to encode data using key equal to data

For some project, I need to store some short string in encrypted form. It would be ideal for the current purposes to encrypt it using itself. ...
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55 views

Adding a Random component to CBC MAC in order to enlarge the tag space

CBC MAC that is using AES as the underlying block cipher, has tag space of 2^128. If we add a random single block, concatenating it with the tag, and encrypt it again in AES CBC mode, with additional ...
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470 views

How to decrypt a '.enc' file that has been encrypted with RSA using a public key? [closed]

While solving a CTF challenge online, I came across a situation where I needed to decrypt a '.enc' file that has been encrypted using someone's public key. The ...
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109 views

Is the keystream transmitted with the ciphertext when a stream cipher is used?

When a stream cipher is used and a keystream is generated to be XOR'ed with the plaintext, is the keystream sent with the ciphertext so that the receiver knows how to decrypt it? Or does the ...
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551 views

Is it safe to use PBEWithMD5AndDES?

I'm encrypting some of my (not so much important) files with PBEWithMD5AndDES. Is it a strong method or it can be de-crypt easily without knowing my selected ...
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97 views

How do you implement a cipher as one lookup table?

I am reading up on whitebox cryptography and have trouble understanding how are ciphers implemented as one lookup table? assuming my plaintext is just 4 bits so the size of my lookup table should be ...
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83 views

Difference between the TLS cipher suites?

TLS_DHE_DSS_AES256_CBC_MAC / TLS_DHE_RSA_AES256_CBC_MAC Hi, I have been studying to learn about various cipher suites and their performances. I gathered that DSS is efficient when compared with RSA. ...
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227 views

What is the most light-weight symmetric cipher thats still usefull?

I need a very light encryption scheme which costs almost no performance during encryption (while decryption may be slow). I found 5 algorithms: RC4, DES, LED, PRESENT, and Piccolo. But how do I ...
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86 views

why do files downloaded with http and https have the same size?

while working with Encryption mostly cipher text is always larger the plain text, why isn't that the case when downloading a file using https ? even that compression isn't much used anymore because if ...
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103 views

Block cipher mode with diffusion on ciphertext

As I understand, diffusion property in AES-CBC ensures that one-bit change in plaintext will yield changes in all following blocks in ciphertext upon encryption. I'm looking for algorithm that will ...
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124 views

Repair AES-128 decrypted file

I decrypted a file which was encrypted with OpenSSL and AES-128 with the wrong password. Before I noticed it was the wrong password I removed the original file. Is there a possibility to reproduce the ...
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51 views

What is the probability of finding 4 equal bytes? [closed]

Is it $2^{-32}$ or $2^{-24}$ as one byte is assumed to take a given value and the remaining 3 bytes should have the same value?
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1k views

Twofish vs. Serpent vs. AES (or a combo)

I've seen some posts and info online, but they are from 2009, 2010, 2011 or 2012, which is 3-6 years ago, which is a very long time. So I'm looking for an up-to-date answer about which of these is the ...
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1answer
107 views

Figure out the encryption being used [closed]

There is a web API (for a game) that sends and receives data encrypted in hex format. I'm interested in accessing the api outside of the game client (mobile app). When sending a request with an ...
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117 views

Simple multiplication as an encryption method

There was a time when I wondered about multiplication as an encryption operation. That was when I was thinking in terms of modular multiplication. But how about based around simple multiplication. ...
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135 views

Client-Server application how can data be encrypted so only clients can read it

Requirements We are building a system that connects multiple clients through a restful API. It allows the creation of groups of trusted clients. We need a way to store group shared data encrypted ...
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Counter Mode with a sequence of zeros bits plaintext, is it secure?

I had a quiz last week in computer security course. There was a confusing question that I am still looking for a good and clear answer. First, I know that counter mode with a good block cipher is ...
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RSA generation of private key using public key

In RSA private key generation e*d ≡ 1 mod φ e is public, also n is public. How to prove mathematically, generation of ...
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CPA security of a stateless and deterministic encryption system

Why can no stateless and deterministic encryption system be IND-CPA secure? Is there a formal proof for it?
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RSA signing security

I'm curious about the security of RSA signing with the same public private key pair when the same message is sent multiple times. It's my understanding that once you generate the hash of the message ...
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97 views

Automated testing of cipher security for import/export compliance [closed]

What do we know about systems that automatically test and grade cipher security. The application in mind would be for checking for compliance with import/export regulations. I imagine a system that ...
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1answer
107 views

How to implement the Salsa20 hash function?

I am currently implementing Salsa20 from the specification as an exercise in learning and self-flagellation. I have Sections 1-7 passing the test examples provided. I am now stuck on Section 8, The ...
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what is it called when encrypt('a') + encrypt('a') == encrypt('aa')?

So normally if you do encrypt('a') twice in a row you'll get the same result. But sometimes (as is the case in SSH) this is not desirable. You want encrypt('a') + encrypt('a') == encrypt('aa'). What ...
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What would be the best plain text Cryptography method without the use of a computer? [closed]

What would be the best Cryptography method without the use of a computer? This could be a list of the current options available, that could be used without the use of a computer ...
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185 views

Secure double encryption using CPA and CCA

Do you mind if you give me any hints, links or ideas about how to improve the security of double regular encryption and decryption, by using CPA game and CCA game, it sounds interesting question, and ...
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Why has SSL v3 not yet been upgraded to a higher version with stronger principles, what are the dependencies and issues to do so?

SSLv3 is almost 18 years old; why has it not been updated to a more advanced version with stronger rules and structure. What have been the issues and dependencies in doing so till now???
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Determining message given cipher-text and public key [duplicate]

Consider the following scenario: Suppose A and B have set up their RSA public keys, namely $(e_a, n)$ and $(e_b, n)$, where the n-value is the same. Also, it happens that the $\gcd (e_a, e_b) ...
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307 views

how to calculate non linearity of AES S-box?

S-box has to satisfy different design criteria. How to calculate non-linearity , propagation criteria for an AES S-box?
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79 views

Prepending random data to encrypted file

If random data is prepended to a file encrypted with GNUPG's symmetric encryption, how may an attacker find out if the input file is deliberately corrupted or the passphrase is wrong? If it is not ...
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99 views

blowfish ecb with openssl doesn't give the expected result

I do the following via the Linux CLI: ...
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120 views

A variant of Shamir secret sharing

Suppose implement the Shamir secret sharing as following: we select a degree $d$ polynomial $P$ with a zero coefficient of 0, and all other coefficents selected randomly from $Z_p$; and to this ...
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62 views

What cryptographic paradigm is appropriate for this use case?

This is a very newbie question... I have to quickly implement a solution for our application that works like this... We have a binary executable that is given a configuration file. I need to encrypt ...
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416 views

Decrypting a small Message using RSA with a Private Key [closed]

If I have a private key of (43, 341). What would be the steps I need to take to decrypt a small message using RSA? I have looked ...
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encrypting data signals using the time variations between two independent coupling functions [closed]

There was a recent article about a new encryption technique that encrypts "using the time variations between two independent coupling functions". What is this technique they are referring to?
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Is substitution with random prefix codes secure? [closed]

The following paper interests me very much: D. W. Gillman, M. Mohtashemi, R. I. Rivest, On breaking a Huffman code. IEEE Trans. Inf. Th. Vol.42 (1996), pp 972-976. However, unfortunately due to my ...
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Can you prove the existance of a PRG $G$ s.t. for each even $k$: $G(k)=G(k+1)$?

In one of the exercises in [KL] Book I need to tell whether an encryption scheme is secure under an eavesdropper of only one message. Given a PRG $G: \{0,1\}^n \rightarrow \{0,1\}^{n+1}$. The ...
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157 views

ElGamal encryption with private key [closed]

Does the encryption with a private key and decryption with a public key works in ElGamal likewise what is done when we use RSA for sender authentication?
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160 views

How to store keys for a cascading encryption?

What is the best way to implement a cascade encryption? I'm trying to figure out how to cipher a string (or message) using Serpent-Twofish-AES and then store the keys. I'll provide an explanation, ...
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461 views

WIN LM Password Hashes (using John the ripper) [closed]

In a problem set, we've been asked to use John The Ripper to crack a list of Win LANMAN passwords. They are of the following form: 953A55E36AB85C0B9DA92C18555E42E1:0169295E0A6A6B35B2DD9932D10C1978 ...
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981 views

My encryption message system & question about security

I made this small tool for make & read easily an encrypted message without nothing to install, just a simple private key like a word or a couple of words to share. (Without say it directly of ...
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451 views

How does certificate-based encryption solve key revocation problem?

How does certificate-based encryption solve key revocation problem? For example, if a user accidentally reveals its secret key or an attacker compromises it, the user may request revocation of its ...
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How to choose the appropriate public (i, m) and private (j, m) keys?

I studied some encryption and decryption and I have found some very interesting problem to solve on the internet. I hope I am writing to right site - there are so many in StackExchange otherwise I ...
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255 views

Solving congruences using PARI

I'm having trouble finding info in the docs about how to solve a system of congruences. The closest I can find is 'matsolvemod' in here: ...
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271 views

How to plot the distribution of a ciphertext?

Is there any plot or visualizing program that can plot the distribution of a plaintext and then the distribution of the ciphertext after applying a ciphering encryption algorithm? I am interested ...
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Standards to be a good cipher

I'm not sure I even understand this site, but based on what I see, how can one tell if a cipher is a good one-at what level is it considered good?
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67 views

ElGamal scheme attack when one message is known and ciphertexts are intercepted

Let $G$ be a finite cyclic group of order $p$ and let $pk = (g, h=g^a)$ and $sk=(g,a)$ be Bob's ElGamal public/secret key pair in $G$. To encrypt a message $m$, a random number $r$ is selected and a ...
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HMAC-SHA1( secret key ) with header of a transmitted file

Given: an AES-128 secret key (ASecKey) encrypts a file (CBC mode). (Assume good random) Is is insecure to append (include) an HMAC-SHA1 of ASecKey to file? Purpose: The receiver can then quickly ...
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What is Polymorphic encryption? [closed]

Well i have downloaded some cryptographic algorithm. Do there are those I didn't understand so this is my question: What is polymorphic RC4 or Polymorphic xor encryption? I heard this in malware ...