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 TLS_RSA_WITH_RC4_128_SHA still a secure cipher to use? [duplicate]

I have read numerous times that the RC4 cipher itself is considered broken in TLS. Still many websites are using the TLS_RSA_WITH_RC4_128_SHA configuration even to date. Now, I know that sometimes ...
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How to retrieve the plaintext of a substitution ciphertext?

So the other day, I was piqued by a ciphertext that was trivially encoded through substitution. Solvable only because we can use our eyes to determine word boundary word detection, etc. Trawling the ...
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72 views

How to decrypt a text which is ciphered same length key? [duplicate]

I have ten piece of ciphered texts. I know that they ciphered with a same-length key. Any idea how I can decrypt the ciphertexts? What kind of algorithms should I use? What are the points of taking ...
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Back up an information as $n$ pieces and require exactly $n-1$ to recover it

Let $X\in \Bbb F_2^p$ be some information. How do I create $Y_1,\dots,Y_n \in \Bbb F_2^q$ so that having less than $n-1$ of the $Y_i$s gives you no information on $X$ but having $n-1$ of them allows ...
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Size of p in ElGamal cryptosystem?

In the ElGamal cryptosystem, I was wondering whether the $m$ (message) should be less than $p$ (large prime). Because on decryption, we are getting $m \bmod p$. For $m \bmod p$ to be equal to $m$, ...
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2k views

Why is Triple DES not vulnerable to meet in the middle attacks?

Consider the Triple DES encryption calculated as: $$C= E_{K_1}(D_{K_2}(E_{K_1}(P))).$$ For a chosen plaintext attack, given plaintext $P$, we compute the result of $D_{K_2}(E_{K_1}(P))$ and store ...
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Is RSA in a ECB-like-mode safe for bulk encryption?

Let's say I would like to communicate with my friend using asymmetric/public-key encryption, e.g. RSA. (Note: I do realize that in practice this is done through an intermediate symmetric key, but ...
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192 views

When is it safe to not use authenticated encryption?

I have read the post Why should I use Authenticated Encryption instead of just encryption? When is it safe to not use authenticated encryption? I assumed hard drive volume encryption or per file ...
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Why do we use encrypt-decrypt-encrypt (EDE) in 3DES, rather than encrypting three times?

I'm wondering why we use encrypt-decrypt-encrypt sequence in 3DES with three keys instead of three times encryption with three different keys?
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138 views

Encrypting a short phrase into two keys. both with length of 32letters

It doesn't need to be crazy secure. I wanted to figure out if there's a popular practice when encrypting a short phrase (less than 32 letter long) into two keys (two strings 32 length). Doesn't need ...
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1answer
413 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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687 views

Can I encrypt user input in a way I can't decrypt it for a certain period of time?

I run a baseball league and would like to do silent auctions for free agents. This would require teams to enter their highest bid and the highest bidder at the end of the auction period would win. ...
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2answers
462 views

DES with actual 7 byte key

Do we have any library or any mechanism where we can use true 7 byte key for DES instead of 8 byte key. I need it for keys analysis in DES and 8 byte key requirement for associated library is creating ...
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2answers
263 views

What is the limit of plaintext required to break the Vigenère encryption?

A theoretical question about the Vigenère cipher: Without any knowledge about the key (not even it's length) can we tell how much known or chosen plaintext is needed for the adversary to completely ...
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Is modern encryption needlessly complicated?

RSA, DES, AES, etc. all use (relatively) complicated mathematics to encrypt some message with some key. For each of these methods, there have been several documented vulnerabilities found over the ...
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1answer
41 views

Why Distance-128 relation in Plain texts is reflected in Cipher texts

The two text having relation as "\x10\x11" → "\x90\x91" (80+10) will have relation after encryption/decryption also in RC4. Following code clearly describes the problem I am mentioning. ...
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3answers
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Difference between stream cipher and block cipher

A typical stream cipher encrypts plaintext one byte at a time, although a stream cipher may be designed to operate on one bit at a time or on units larger than a byte at a time. A block cipher ...
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2answers
158 views

reverse an identicon to its source string

Identicons are used to create unique images based on IP address or strings. Lots of programs are available to generate identicons based on an input string. My ...
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1answer
134 views

How do you test the security of your cipher? [closed]

I got asked this question and I didn't know what to answer. How do you test the security of your cipher? What comes to my mind now would be to test it with famous attacks: padding attacks, ...
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How do decryption algorithms determine whether your attempted passphrase is correct?

Judging by the algorithm on the Blowfish Wikipedia article, there is no way for the process to fail with an error. How then does GnuPG know when to tell you your password is correct when decrypting a ...
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Paper about this secure P2P idea?

Two or three years ago, I was reading something interesting, but then I lost the paper. The paper described building secure and fast P2P networks (not like tor or I2P). Unfortunately, I only remember ...
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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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93 views

Simplified Key Wrapping to Achieve Only Confidentiality?

I'm looking for help in understanding why the algorithm described here would not deliver adequate protection of confidentiality. We don't care about other criteria such as authenticity or integrity. ...
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3answers
539 views

Is there a cryptographic method to add noise to a plaintext instead of actually encrypting it?

I'm looking for a cryptographic technique that instead of permuting a cleartext, would add noise to the cleartext to obfuscate the true text among a bunch of garbage. For example, a list of 10 ...
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1answer
165 views

Repeated Encryption using same/different Encryption systems [duplicate]

I would like to know if there are any security risks/gains from encrypting twice, i.e. $$\text{plaintext}\xrightarrow{encrypt}\text{intermediate text}\xrightarrow{encrypt}\text{ciphertext}.$$ I would ...
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141 views

XORing a header with SHA512-hash - secure?

I am writing a application that encrypts text several times and stores the result. The result looks like complete random bytes, therefore I add some random bytes at the end. To let the program know ...
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72 views

The specification of modern, non-communicating cipher machinery [closed]

I'm looking for references, papers or guidance on a class of system which I have not seen widely discussed. Consider powerful electronic machinery which remains in the custody of communicating ...
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1answer
295 views

Abstract algebra in cryptography [closed]

I have taken a course in my undergraduate on the theory part of abstract algebra.Now am interested to know how can abstract algebra be applied to cryptography.Thanks
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Is HMAC necessary if the AES ciphertext of a message includes the CRC of the message?

I've seen that encrypting an image with AES-CBC then calculating the HMAC-MD5 value for authentication is a somewhat common and sound way to secure data. Alternatively, can I just calculate the CRC of ...
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1answer
68 views

Using beginning of TLS ecnrypted data to reveal secret [duplicate]

I have the following question about TLS security: Assume TLS-PSK protected HTTP with AES256-CBC cipher. When a TLS connection is established, client sends some encrypted data, where the plaintext is ...
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1answer
92 views

Encryption mode with chained algorithms

Suppose that I want to encrypt some data using two different algorithm chained (e.g. AES and Serpent) and harnessing the benefits of CBC. I can do: ...
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1answer
367 views

Usage of different size chunks during AES encryption/decryption

I want to encrypt user's files on our server. For this purpose I decided to use the PHP Mcrypt library. I chose to use the Rijandel-128 algorithm and CBC mode for encryption. Since files are quite ...
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1answer
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Implementing OpenSSL padding

I'm conducting an experiment dealing with differences in padding across different aes operations for my Intro to Crypto class, and the question says OpenSSL uses PKCS5 padding, and that I need to ...
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Cryptography Implementation in software

I am trying to implement a password manager in C and I had a question about the proper steps in implementing the crypto. I looked at some implementations, google talks on crypto and what the standards ...
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156 views

Is the strength of RSA over quadratic or other cyclotomic fields as strong as over the integers?

If we assume the strength of RSA is based on the difficulty of factoring (which I know we can't guarantee) and we compose the modulus of some other quadratic ring that is a unique factorization domain ...
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1answer
170 views

The relationship between the key length and encrypt time in Xor algorithm?

I did work on the encryption algorithm and the decryption using the XOR method noticed that when more the key length, the less time spent on encryption and decryption. I have two questions in ...
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Positioning of keys in encrypted text

I'm just looking at very simple encryption. I've noticed that the key is typically either at the front or at the back of the encrypted text. This is quite easy to break if you know the key. It can ...
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1answer
359 views

Does ElGamal Encryption create a different key for each block sent?

I ask about ElGamal algorithm. Is ElGamal algorithm used new key for each encryption process. in other word it should we use new key for each chunk? For example, if we have message that has four block ...
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2answers
185 views

does re-encrypting the same value with multiple keys reduce security

I found myself wondering today, how much security is lost if you take a plaintext - assume that its content, including any metadata is unknown to an attacker, for example it may be random data - and ...
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How we transfer 128bits cipher to a 4x4 matrix for AES input?

Why the input cipher for AES encryption, can write in 4x4 matrix with 8 bits entires, and can said is 128bits? if each cell is 8bits in binary, how we said this matrix is represent 128bits?
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Index of coincidence for completely random text over k alphabets

I'm confused about /Friedman's method 2 (using a table with column of k size of key, and n/k rows, n is the total size for cipher text) \begin{equation} m = ...
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An example of Knapsack Cryptosystem cracks/attacks? [closed]

I have been studying papers on various ways to crack the knapsack cryptosystem, unfortunately the mathematics in these papers involves lattices and LLL which is over my head. The paper "New Attacks ...
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1answer
305 views

SHA256-based stream cipher

Can anyone comment if the stream cipher described here is safe? The author claims it to be unbreakable, but does not provide any evidence or proof to support this. For completeness, I have reproduced ...
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1answer
126 views

IV = Filename XOR CipherKey?

i want to encrypt transparently using Rijndael. So this is, what I thought of and I would like to have an opinion from "Experts" whether this will harm encryption strenght. I am using chunks of 1MB ...
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1answer
453 views

Secure AES Key Generation via Salsa20?

I am not creating my own cryptography or anything, but to learn about the Dos and Donts of cryptography, I am looking into AES encryption and ways to generate keys for that. As far as I've ...
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1answer
83 views

Compression step of PGP

We do compression in PGP. Does this step increase/decrease or either have any effect regarding the authentication of a message?
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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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Prefixing data before encryption for passphrase confirmation?

I'm encrypting data with AES, using CryptoJS. CryptoJS returns an empty string in case the data couldn't be encrypted with the given passphrase. I'm not sure if this is intended, or happens in all ...
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238 views

Is that possible to use encryption higher than 256-bit?

When browsing websites with Chrome sometimes I can see a green lock and encryption info inside. It says the connection with this website is 128-bit or 256-bit encrypted with TLS1.2. So I'm wondering ...
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Key-dependent encryption in TAHOE-LAFS

TAHOE-LAFS uses a form of "key-dependent encryption", in that a private key SK is encrypted with the truncated hash of the private key: ...