# Questions tagged [encryption]

a transformation of information to make it unreadable to outside observers

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### equivalent sub-keys in DES encryption

i am trying to understand the DES cryptosystem and was wondering: what would've happened if all of the sub-keys were equal? does it reduce the security? can we actually find the keys if we know all ...
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### Period of sum of two periodic sequences

I was wondering, what is to be the shortest possible key using Vigenere encryption, if a text is ciphered one time with a key of length $i$ using Vigenere and second time with a key of length $j$ ...
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### Determining key from plaintext and ciphertext (Vigenère)

I was wondering why mathematically we can know the key in the Vigenère cipher if we know in advance a message and its encryption.
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### Can reducing NP problems to subset NP Problems leed to faster calculation of NP problems

Integers can be represented with a pair of smaller numbers. To achieve this I use 2 integer sequences. Integer Sequence 1 1,1,2,1,2,3,1,2,3,4... And Integer Sequence 2 1,2,1,3,2,1,4,3,2,1... This ...
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### Weaknesses arising from using same key in both channel directions

I came across the following question: Which of the following risk may arise, when same key is used to encrypt both directions of a communication channel, that are not present if using different keys ...
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### Perfect Probabilistic Encryption still requires key length about as long as message

Let $(E,D)$ be a probabilistic encryption scheme with $n$-length keys (given a key $k$, we denote the corresponding encryption function by $E_k$) and $n+10$-length messages. Then, show that there ...
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### RSA cryptosystem: Encrypting a signed message

I've started to read the section about the RSA cryptosystem in CLRS (page 958) and I don't understand the way it describes how to encrypt a signed message. If Bob wants to send a message $M$ to Alice:...
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### A tree-like data structure with rights delegation for distributed computing

Every actor can create a root node and delegate a right to add a child node. Every node contains name of its’ creator or who added it, and value S. Sum of all values S at the same level of the tree ...
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### Structure Preserving Continuous Hash Function

This question was originally posted on super user, but redirected here based on some suggestions. I am completely new with computer science, and not only recently did I run into the notion of hashing....
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### Why don't most websites I visit seem to use TLS with Ephemeral Diffie-Hellman?

When I click "view certificate," under Public Key Algorithm it usually says "RSA Encryption" or "Elliptic Curve Public Key." I assume this is the algorithm used to agree on a premaster secret (...
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### Why does Feistel encryption algorithm encode half block every time?

Why does Feistel encryption algorithm encode half block every time? What would happen if the entire block is encrypted in each step?
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### What is the point in hashing a value?

I apologise if this is not the right place for this question... I didn't want to ask on Stackoverflow or CodeReview as it will closed in minutes as "too broad". A client of mine is writing an API ...
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### Finding small-length RSA private key

I was wondering if there is an algorithm to derive $p$ and $q$ or is it simply trial and error? Consider the following RSA crypto-system with public key $(437,13)$. Since the numbers are so small, ...
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### DES encryption - what happens if all sub-keys are the same?

What will happen if we change the DES encryrption algorithm to use the same key in each round ? How will it affect the encryption - will it only make the encryption same as decryption or are the more ...
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### fully homomorphic encryption with information-theoretic security?

An encryption algorithm with information-theoretic security is one which even with infinite amount of computation cannot be broken. That is, given only the ciphertext, no amount of computation can ...
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### How can a fully encrypted homomorphic program resist copying?

Let's say that we have an original homomorphically encrypted program with any possible code inside. What methods can it use to ensure that it is impossible to create an exact copy of it? Are there ...
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### Finding $d$ in RSA Encryption mathematically and by hand

I'm working on this RSA encryption problem and the catch is that it must be done by hand and mathematically. Let's say $p=11$, $q=13$ $$N=p \cdot q=11 \cdot 13=143$$ I chose $e$ to be relatively ...
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### Can I prove that I have x such that f(x) < c without revealing x?

I'm interested in applications to verifiable computing. Let's say Alice would like to find an x such that f(x) < c for some real-valued function f and some c of Alice's choosing, so she hires Bob ...
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### Can software itself be encrypted?

Imagine that I need to install my server in a remote location, so my algorithm can do something fancy (collocation of server at a financial exchange is how I thought of this question, but it applies ...
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### Given a string, is it possible to determine which hashing algorithm has produced it, if any?

Given a string, is it possible to determine which hashing algorithm has produced it, if any? For example, the MD5 hash of "string" is b45cffe084dd3d20d928bee85e7b0f21. Is it possible to determine ...
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### What are the flaws in this encryption algorithm?

Let $A$ be a randomly generated matrix. Let $I$ be the identity matrix. $\times$ is the matrix multiplication operation, $/$ is matrix division (multiplying the first matrix by the inverse of the ...
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### Is my interpretation of the SSL process correct?

Firstly, which of the two diagrams below is the more accurate or more well-explained (if both are accurate) representation of the SSL process (at a beginner's level)? Diagram 1 Diagram 2 Also where ...
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I am having a very difficult time trying to understand what exactly this question is asking. How many valid English plaintexts are there for the ciphertext message CJU using a length-3, one-time ...
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### Data Compression Algorithm for Less repetitive pattern (redundancy) [duplicate]

Context: Lossless Data compression (source coding) algorithms heavily rely on repetitive pattern (redundancy) Questions Which data compression method/algorithm deals with less repetitive pattern (...
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### If P=NP, are there cryptosystems that would require n^2 time to break?

If P does equal NP, will it still be possible do design a cryptosystem where the optimal cryptanalysis algorithm takes, say, the square of the time taken up by the legitimate encryption and decryption ...
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### Monoalphabetic Cipher Key

I am not sure how to get the key for the following Monoalphabetic Cipher question. This is a textbook question and I know the answer, but I juts dont know how they got the key. Question: Decrypt ...
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### Encryption on a compressed file

Can I do encryption on a compressed file and again decompress the file after decryption to get the original data?
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### What if p and q are not distinct in RSA Crypto System? What could go wrong?

In RSA Crypto System we choose p and q such that they are distinct primes. Calculate n=pq and phi=(p-1)(q-1). Then e is chosen for public key (n,e) s.t. gcd(e,phi)=1
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### Issues in RSA setup

Suppose we have public key: $$n= 1015, e= 3$$ and private key: $$d= 635, p= 35, q= 29, \phi(n)= 952$$ For $m = 100$, we have $$c = m^e ~mod~n = 100^3 mod~1015 = 225.$$ To decipher this, let us ...
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### How to revert a carryless polynomial multiplication?

In the carryless multiplication of two polynomials in a 8-bit environment, is it possible to obtain the original 8-bit values from the result? As an example: \begin{align} (x^{11} + x^{10} + x^9 ) ...
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### Running an algorithm on data remotely and ensuring answer has not been tampered with

I´ve been thinking about this particular computing/crypto/database problem for years and I just want to know if there are already solutions to it. To be honest I don´t even know what field this ...
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### RSA Encryption & Anonymity

Considering plain RSA encryption, assume we have B who wants to send 10 messages to either A1 or A2. The recipients' public key, namely the exponent e1, e2 and prime product n1, n2 for A1/A2 ...
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### Formula for sufficiently lengthy encryption key?

As you add length to an encryption key, at some point the message becomes impossible to brute-force decrypt. This is because at that point, if you go through all the possible keys, you'll get many ...
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### RSA Decryption from Simple Public Key Values

I'm a little stuck trying to figure out how to decrypt some messages and could use some hints as to what I may be doing wrong. I was given a series of integer values that make up my cipher text. Here ...
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### Is running AES NI in parallel possible (one encryption per core/thread)?

AES NI seems to perform AES operations much faster than doing in software. However, if I have a machine with a large number of cores (say 32 cores), can I perform 32 AES encryptions using AES NI ...
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### Data Compression: Which one is Better “Compress before Encrypt” or “Encrypt before Compression”

Which one is better approach do data compression before encrypting it or Encrypt data before compression ? I think it is biased towards the application requirement. Please share your views.
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### One time pad, get plaintext using ciphers encoded with the same key

I'm trying to solve a problem: I have 11 ciphers encoded with the same key. My aim is to decode target cipher. If I do xor C1, C2 (ciphers encoded with the same key) I do get M1 xor M2 (where M1, M2 ...
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### After implementing a novel encryption algorithm, how would one go about analyzing its security or get help from others in doing so?

Preface: This question was originally asked on Theoretical Computer Science, and the kind people there referred me to this web site. It is being repeated here in an attempt to find a satisfying answer....
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### How can encryption involve randomness?

If an encryption algorithm is meant to convert a string to another string which can then be decrypted back to the original, how could this process involve any randomness? Surely it has to be ...
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### Key secrecy vs Algorithm secrecy

it's a well known statement that "Cryptographic security must rely on a secret key instead of a secret algorithm." I would like to ask about some details about it. And which are their differences? ...