# 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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### Perfect Secrecy and Message distributions

It is know that for a perfect secrecy scheme, for all m1,m2 and c: $Pr[C=c | M=m1] = Pr[C=c | M=m2]$ I also know that for all distributions of M, m1,m2 and c: $Pr[M=m1 | C=c] = Pr[M=m2 | C=c]$ Does ...
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### Automorphism in Cryptography

I read a research paper in which the writer again and again writes about norm preserving automorphism such as $\left \| \phi(a) \right \|$ =$\left \| a\right \|$ and determinant preserving ...
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### Is anyone using Half-Bit encryption? What is it used for now?

Long ago I learned about an encryption scheme which uses a random mask of bits which were "half on". I don't recall all the details, but basically, if a mask bit was a one, the input bit was passed ...
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### Is there a reduction of security if I XOR Pkcs5S2 and SecureRandom?

I'm using this codereview sample to encrypt data. I would like to provide hardware protected encryption and a user password as the key. Is it acceptable to XOR the KDF Pkcs5S2 in Bouncy Castle with a ...
28 views

### Rotate values in predefined manner

I want to create a Server S1, that publish a different value every 10 minutes on the internet. The value looks something like f7826da6-4fa2-4e98-8024-bc5b71e0893e. ...
162 views

### 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 ...
246 views

I know it's generally bad to store password in the clouds, and that I should be using salted-hashed password only. I'm making an application that will authenticate a user (with salted-hash), and then ...
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### Permuted Hash Table

Suppose we have a hash table, $HT$, consisting of $100$ bins.The hash table uses a hash function $H$ that is public. We all know that given value $a$ we can compute the address in the hash by $H(a)=j$...
57 views

### When we use permutation and random long sting to hide a message

This question is modified version of this: Can we use merely permutation to hide a message? I have an English name $m=m_1 || m_2 ||..||m_{30}$. I pick a random string $d=d_1 ||..||d_{70}$ I mix ...
192 views

### Symmetric encryption with compression for MySQL DB data

I would like to compress data before encrypting and storing it in a MySQL DB to reduce especially bandwith requirements (compression reduces bandwith by 70-80%). At present, all is handled by a server-...
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### Having doubt in Rijndael Algorithm- coding for decryption

I am doing a project on the Rijndael Algorithm. I have already written the encryption code which produces the correct output. Now I want to implement decryption as well. I'm doing using VHDL, ...
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### Batch ElGamal Scheme

I know about ElGamal scheme and its key generation, encryption, and decryption methods. I'm not sure about what is meant by batch ElGamal. Can someone please clarify it. How it differs from ElGamal ...
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### Is it possible to have E=D and Ke <> Kd?

Let us consider $E$ an encryption algorithm that encrypts a message $m$ into a ciphertext $c$ using a key $K_e$. i.e $c = E(K_e, m)$. Similarly, decryption is achieved by $m = D(K_d, c)$. Is there ...
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### Defining correct secured channel from endpoint to server

I'm new to cryptography and have a question regarding encryption usage. The scenario is as follows: I have an endpoint hardware device (CPU - ARM A7 1.2 ghz) which runs Ubuntu 14.04. This hardware ...
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### How to implement order-preserving encryption without CryptDB

Which cryptographic algorithm is suitable for implementing order-preserving encryption without using CryptDB?
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### Can a combination of encryption algorithms weaken the overall encryption?

Are there any instances where a combination of industry standard encryption algorithms can weaken the overall encryption of the data? As a Naive example using non-standard encryption algorithms, ...
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### Rabin cryptosystem with 1 mod 4

We have p and q which are distinct primes congruent to 1 mod 4. Then we have n = p*q. Do you know any algorith for calculating square roots for the decryption in this case? I'm asking for some ...
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### Is ASCON cipher broken?

http://eprint.iacr.org/2015/030 present several attacks of ASCON but does not have a conclusion section. I'm having troubles estimating what are the consequences on the use of ASCON. What's your ...
556 views

### Brute Force AES Calculations

I have an encryption service in which the user decides the length and the type of key, so I would like to build a tool that educates the user on the brute force times for the key they created if using ...
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### fuzzy commitment implemenation to make secure biometric template

I want implement some ideas from an article that is about making secure biometric templates using fuzzy commitment and fuzzy vault. I need to implement just the fuzzy commitment (fuzzy commitment is a ...
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### 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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### Cryptography system that limits the length of the encypted message

I have two devices which communicate via sms. This communication should now be encrypted. The devices can only send messages with the lenght of 160 characters. So i am looking for an encryption ...
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### 2048 vs 4096 bit RSA keys

I am in the process of creating an app which has secure encrypted messaging. I am generating RSA keys when the user signs up with key size 4096 right now. The problem is on the web these keys take a ...
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### Alternatives to XTEA as encryption algorithms for stenography

I recently implemented an algorithm written in Python that was using the XTEA encryption method. Are there any more reliable algorithms than the XTEA , regarding to memory usage and PSNR ratio ,other ...
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### Asymmetric encryption that preserves the plaintext size

I'm looking for an asymmetric encryption algorithm that preserves the size of the thong in clear text. The encrypted file must not be longer than the plaintext file and must not contain any special ...
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### How should I assign a letter at random to another?

For my first ever project in Python, I wanted to code a cipher to encrypt simple messages ( no spaces or lower case to avoid that extra hassle for now ). My idea was to either: Choose a letter of ...
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### How to find the key of XOR encryption in Java?

I am trying to find the key of an XOR-encrypted string in Java. It is very probable that the key is eight characters long. I have the encrypted string. I do not understand how to go backwards and ...
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### XOR of users password Scrypt key and Random 32 bit salt?

I am trying to encrypt users private keys with the user password but if a user provides a weak password then the scrypt key generated from it will also be weak and suspectible to attack. Let say the ...
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### How can I protect AES-256 encrypted data?

In April 2017, Jacob Henning asked "What are the chances that AES-256 encryption is cracked?" and part of his question was how best the transmitted data, now in his web database, a.k.a. "data at rest" ...
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### Encrypt 2 numbers preserving arithmetic correlation

I want to encrypt 2 numbers using a public key and have the reader know the correlation between those 2 numbers. I can also share the public key. Example: ...
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### how to encrypt the chat message with multiple people public key together and restore the message?

I have a application with two users and one middle man, all of them holding the private and public key, To make the secured chat, two users and one middle man are all sending the public key and ...
129 views

### Reversing key exchange algorithm

I'm analyzing some software and finding key exchanging procedure. Its looks like very similar with Diffie–Hellman, but not the same. I can’t understand the purpose of this. The step of algorithm is: ...
1k views

### RSA : if my key and message are too large , how to do?

I want to send a message consisting of a string of number (e.g: 124124134235235) Then, p:125243 q:56454547 e: 2659043 d: 5261378624675 However, it will be too large...so, is there any solution to ...
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### GMW Protocol with semi honest adversaries

I know the GMW Protocol is secure in the case of a semi honest adversary which control all the parties except one. However I want to proof that it is also secure in the case the semi honest adversary ...
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### How to make sense of the decryption formula for Affine ciphers?

Hi guys so I'm investigating Affine ciphers and I need to understand a field of mathematics I'm not familiar with, which is modular arithmetic. The formula for encrypting a letter $x$ using the affine ...
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### Encryption algorithm designed to be easy to decrypt by machine but impractical to decrypt by hand

I am looking for - or considering the design of a new - encryption algorithm that does not use variable keys, such that it is easy for a computer to encrypt and decrypt any message regardless of its ...
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### Encrypted file sharing with deterministically generated key from user password

Background info: I need to encrypt files in a enterprise workspace with several users. The goal is to encrypt files directly from browser to be saved on a server and each user could decrypt files for ...
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I have an OLD work database that seems to have a simple encryption on the PW. I have one users whose pw is 7777 the cipher text is ...
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### FEAL-4 Fk Function 4 Rounds

As I understood in FEAL-4 it needs 4 pair of round keys. Which means that we need to launch Fk function 4 times. My problem occurs starting the 2nd round. At the first round we have the original 64 ...