# Tagged Questions

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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### Recryption of ciphertext with a different key

Let's have $P$ some sensitive piece of data and $K_1$a secret value, both known to Alice, but not to Bob. $K_1(P)$ means $P$ encrypted using $K_1$. Alice sends $K_1(P)$ to Bob. Bob keeps the value of ...
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### How is the message digest related to Signatures and Encryption?

I was studying about 'Data Security' and I found out this one thing confusing. What is an message digest? I got it is the hash of the message. Is the message here referring to the plaintext or ...
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### How secure is a client-side javascript encrypter?

A friend of mine needed help with her website and asked how to send me her login information securely. I've never known how to do this, so I figured now was the time to learn. After some googling, I ...
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### homomorpic encryption [closed]

I am doing project k-nearest neighbor classification over semantically secure encrypted relational data I have doubt for in smin algorithm in 1)Li ← Wi ∗ Φir′; ri′ ∈R ZN this line it the out put is ...
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### Finding Private key in RSA with public key, cipher text and plain text

Is there a known 'non-brute force' method of determining a private key in an RSA system when all other parameters are know? I found the values of a ciphertext ($C$), its corresponding plaintext ($P$) ...
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### Can double-encrypting be easier to break then either algorithm on its own?

As was pointed out in Martin Bonner's comment I cannot prove this, but it seems intuitively impossible. An encryption function is supposed to obscure the plaintext to the point where no information ...
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### MISTY1 encryption/ extension tricks

I'm trying to understand MISTY1 encryption algorithm but i faced some problems in key scheduling part : Key scheduling part consists of the following operations. for i = 0, ..., 7 do EK[i] = ...
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### Which encryption is recommended for own messenger [closed]

I wrote my own messaging-app and now I would like to encrypt the data transfer between my client (app) and my server. What kind of encryption is easy to implement and can be recommended? I am very ...
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### Playfair Cipher Confusion with one column encryption

Recently I decided to learn "Playfair Cipher", and I have hit a road block. what do i substitute the letters for if they are on the same column? Here is an example: ...
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### Is it better to encrypt before compression or vice versa?

Is it better to encrypt a plain text file before compression, or vice versa?
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### Why does AES ciphertext entropy always close to 8?

I have three binary files: 31744 byte length (1), 5712980 byte length (2) and 10806008 byte length (3). The alphabet is all 256 symbols from 00 to ff. I compute the shannon entropy, replacing ...
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### Encryption using two keys

Suppose we have two secret keys K1 and K2, I'd like to ask if there is any encryption scheme that allows us to derive another key K12 from K1, and K2 and for a message x, EK12(x) = EK1(EK2(x)). EK(x) ...
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### Is there an asymmetric algorithm that can perform double encryption?

I'm looking for any asymmetric algorithm can perform the serial encryption, by serial I mean double or more encryption with different key(same key size). RSA can not do it since the cipher of the ...
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### Do these new insights into prime numbers affect encryption security?

Quanta Magazine reports: Two mathematicians have uncovered a simple, previously unnoticed property of prime numbers [...]. Prime numbers, it seems, have decided preferences about the final digits ...
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### X509 converted to Encrypted and Signing keys

We have proprietary tool which takes a p12 file and generates a .key file. Inside the key file, I see two PEM formatted sections: Encrypting Certificate and Signing Certificate. When I open them on my ...
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### Certificateless cryptography Implementation

Hello guys I am trying to implement Certificateless Cryptography algorithm with reference to this base paper. Right now I am trying to implement the code in java. ...
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### Is it possible to create a detection oracle for all block cipher modes? — ciphertext-only cryptanalysis

I have made an ECB/CBC detection oracle, and am now trying to make a detection oracle that can differentiate between CBC/CFB/OFB/CTR/etc. I can already tell ECB apart from the others due to this ...
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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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### In an A5/1 stream cipher, why do the registers have a stepping probability of 3/4

I know that the probability of each register to step is 3/4 but I have yet to find an explanation of why. Can anyone explain this to me?
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### List of post quantum cryptography protocols [closed]

What are the post quantum cryptography protocols that have been proposed until now? I know about McEliece cryptosystem, and LWE scheme. What are the others? Can you provide me a list or a website ...
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### Best non-digital cipher?

Is there an undisputed cipher that was considered the best before the computer age? (This is not suppose to be a discussion, it's either a yes or no.) Please give a brief description why it is yes ...
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### Monoalphabetic cipher using different languages in the same plaintext

Today I learned the principle of the monoalphabetic cipher. It's simple to decrypt a ciphertext written all in the same language (english for example) because I can use the syntactic properties as ...
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### How to encrypt and decrypt a transposition cipher?

I encrypted the text hello there with a 3x4 table with the key 2 1 3. I fill in the text into the table row by row and got the ...
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### Number of shifts in DES key schedule

In DES key schedule some rounds use one left shift while others use two left shifts. What is the reason behind this?
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### Is there any difference between a one-time pad and a Vigenère cipher with a long key? [duplicate]

I've been browsing Wikipedia and stumbled on the article for the Vigenère cipher. I realized after seeing the example that it's quite similar to the one time pad, except with a short key repeated as ...
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### Confidentiality then Integrity with different keys [duplicate]

Can anyone describe how we can do what is said in the below sentence which is in Mark Stamp crypto slides (PPTX) on slide number 101 : Can do a little better - about 1.5 “encryptions” The whole ...
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### Confidentiality then Integrity with different keys

Can anyone describe how we can do what is said in the below sentence which is in Mark Stamp crypto slides (PPTX) on slide number 101 : Can do a little better - about 1.5 “encryptions” The whole ...
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### Calculating inverse of transposition key cipher [duplicate]

I need some help on transposition cryptography. If I'm given the encoding key to a transposition cipher, how do I get the decoding key for it? I tried googling but couldn't find any steps on the ...
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### How to test an encryption against different attacks [closed]

For the last while I have been reading up on cryptography and the different kinds of methods for encryption (public key, blocks, etc) and the attacks against them. This got me wondering how to ...
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### Public-key encryption with associated data

In the symmetric-key world, we have authenticated encryption with associated data (AEAD). I'm looking for something similar, but for public-key encryption: public-key encryption with associated data (...
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### Does encrypting with MGF1/SHA-512/1024-bit seed equal to a 1024-bit key block cipher?

Suppose: Alice uses SHA-512 with MGF1(as in PKCS#1 V2) and a 1024-bit random seed to generate a mask, XORs the mask with a message(M), gets a cipher text (CT), and sends the CT to her old friend ...
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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 ...
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### How to publish a cipher (concept)?

In the last months I was searching for a subject for my bachelor thesis. I came up with an idea for a new cipher concept that works by combining already known techniques in a (hopefully) new way. So ...
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### Could a key derivation function be used to encrypt data with a weaker key?

To allow the key to be more easily remembered. Example: To encrypt a hard drive without having a remember a key with 128 bits of entropy. From what I find they seem mostly used to hash passwords so ...
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### Hash + Salt v. Hash + Encryption

I was wondering if using a salt with a hash is more effective than hashing and encrypting your hash.
Disclaimer: I'm new to cryptography. Background: I'm reading Cryptography Engineering by Ferguson, Schneier, and Kohno, where, in Chapter 2, the authors write this: Question: What is $k(k-1)/2$ ...