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 would the opponent defraud this secure communication?

I am new in the cryptography and the information security problems, I try to understand things as much as I can and I know it's really complicated in the beginning. Considering the communication ...
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Is it ok to store the plaintext hash of encrypted data

Is it ok to create and store the hash (unkeyed hash function) of a plaintext before encryption or does it lead to vulnerabilities? If it is ok are there requirements for the used hash function and ...
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Is there a way to create an encrypted email with no third party application

I would like to send and receive emails between group of people. Is there a way to create it with no need to use some other 3rd party application. Is there a way just to transfer files between 2 ...
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106 views

How to encrypt incomplete block with RSA as a block cipher?

I have a question about an RSA academic example. If we are using block-RSA with a block-size of 3 and we have this message: "android". It is broken into 'and', 'roi', 'd'. How to encrypt the last ...
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74 views

Finding a secret cipher given the key and known plaintext?

Let $x,y,k$ be plain text, cipher text and key respectively. Also suppose $\operatorname{Enc}$ is the algorithm of encryption for block cipher with size $n$. So we have $$\operatorname{Enc}_k(x)=y$$ ...
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Certificate Path Verification of X509 Certificate

I have the trusted root certificate which I am validating using the self signed key. I also have the intermediate certificate, which i am validating using the root certificate. Now when i am ...
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51 views

How to deliver an encrypted message to multiple recipients without revealing keys

Let's say I have generated a private and a public key. I create a message and encrypt it with the public key. I deliver this encrypted message and a private key to multiple recipients. Why would I do ...
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169 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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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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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 receiver(...
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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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310 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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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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260 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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253 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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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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1answer
150 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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3answers
290 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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2answers
423 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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113 views

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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175 views

RSA: how does it work and how is it more secure than symmetric systems

Before starting the question, I know that RSA is naturally a key exchange cryptosystem rather than an antilogarithm fully implemented for encrypting and decrypting data since the length of the secret ...
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131 views

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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141 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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356 views

Remove padding (CBC) from decrypted text [closed]

I have a bit problem with padding. Everything goes fine when I encrypt the text BUT when I decrypt I see some extra characters. Sometime's one character sometimes more and I dont know how to remove ...
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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 system/...
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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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253 views

blowfish ecb with openssl doesn't give the expected result

I do the following via the Linux CLI: ...
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174 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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83 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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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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593 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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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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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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381 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: http://pari.math.u-bordeaux.fr/dochtml/html.stable/Vectors,...
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242 views

Cryptographic Primitive Method

Is there any cryptographic primitive bijective (one-to-one and onto) function for creating cryptographic tools like symmetric encryption/decryption, Hash code generator, MAC, HMAC and Random number ...
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372 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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Secure Cipher Suites supported by JDK versions [closed]

I'm a n00b to cryptography. I've been searching through oracle's java docs, ssl labs, googling and more googling attempting to find an up to date list of cipher suites considered secure for the ...
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25 views

X509 Cert exploit CA check

Assumptions Let's theoretically assume that a browser skips the check that a certificate it receives belongs to the stated CA (that's an exercise). How could I exploit this in order to impersonate ...
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Is it possible to extract the decryption key from a locked android device

Is it possible to extract the decryption key from a FDE android device while the screen is locked but the phone is powered on. Is the data only safe when the phone is off ?
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Fully or partially Decrypting Data with Multiple keys

Is there any good paper or research carried out till now that a data is encrypted by a single key or onwer(user) and their are 2 or more decryption keys. One key can decrypt the entire data. Other ...
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42 views

Calculating characters from the sum of ASCII pairs

I have a series of messages (limited to only a-z and A-Z) that are encoded such that the sum is taken of every two ASCII values and concatenated. For instance, the message ...
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Brute force knowing a part of the password

So here is the problem, my brother forgot about the eight digit numeric part of his password, he is using Ubuntu 15.04 default whole disk encryption To make it clear, this was his password (example) ...
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1answer
56 views

File using same key on XOR cipher. Using CBC [closed]

I have some files that are encrypted using an unknown key and it's using the CBC method to encrypt the files. When I XOR two files together the first two bytes are always the same, but different for ...
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CCA on PKCS#5 using error feedback

My question is about attacking PKCS#5 with CCA using the error feedback. What we learnt in class about PKCS#5: CBC requires padding to whole block boundary PKCS#5: standard padding If ...
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1answer
81 views

Storing RSA private key

Currently I'm developing an application where users generate their own pair RSA keys in order to achieve a secure communication with my server. Also clients are able to communicate directly, sending ...
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1answer
79 views

Breaking One Time Pad with CCA

I was taught that: although OTP is CPA secure, it is not the case with CCA. I'm trying to figure how to break OTP with CCA by showing how it fails the IND test. ...
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Is this method of encryption theoretically unbreakable?

I implemented a Stream Cipher using Cryptographically Secure Random Numbers for the key values. The key stream was as long as the plaintext stream. This key data set won't be reused. Have I met all ...
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Key derivation using the main AES encryption key and some plain text

I am using AES 128 bit encryption in java. I have an encryption key and 10 digit plain text. I want to derive a key for HMAC using the AES encryption key and the 10 digit plain text. This plain text ...