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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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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472 views

Why is it a bad idea to use a UTF-8 derived symmetric key?

Given a cryptographically secure series of octets, it is often useful to display this information or store it in a database in a textual format such as hexadecimal. Why would it be incorrect to take ...
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152 views

What's the safest TrueCrypt algorithm and hash?

I have an encrypted file container inside my NTFS pendrive. The root folder Write permission is blocked for everyone. A folder inside it has all permissions unblocked. The dummy file of TrueCrypt is ...
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68 views

In case M is small is it possible to recover the message

In the plain RSA encryption, suppose $N$ is 1024 bits and the public key $e = 17$. Is it secure to use this setting to encrypt very small message, say $3 \leq m \leq 9$? In other words, is it possible ...
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69 views

Single public key for NaCL signing and encryption?

Bob wants to use NaCL (specifically the Python NaCL library) to both a) sign some publically available plaintext for anybody to authenticate as being written by Bob and b) encrypt some other secret ...
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158 views

How is this for security? [closed]

I have a function in a C++ program that uses a incrementing integral pattern within a algebraic formula. Each time there' a new character inserted, it uses this ...
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69 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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106 views

Use Smart Card to decrypt files

So I'm trying to figure out the feasibility of using a Smart Card to decrypt files in an offline scenario. I wish to sync encrypted files to a mobile phone with a Smart Card reader case. The files ...
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2answers
129 views

How to identify the difference between two cryptographic schemes in terms of security?

I am currently working on a project, that requires using encryption libraries namely (LibScarab and FHEW). I want to know how can I compare the two schemes in terms of security (I already compared ...
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Shannon theorem of perfect secrecy

From the class: Shannon Theorem: For a perfect encryption scheme, the number of keys is at least the size of the message space (number of messages that have a non-zero probability). Proof: ...
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Detecting Encryption in Real-Time

Is there anyway to detect encryption in real-time through a common signature or pattern recognition. Say, a file is being encrypted using an AES-256 cipher, if I have access to the file stream - can ...
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45 views

How should I implement a secure recovery of encryption?

I want to create a system to host as securely as possible encrypted data in a way that not even the system can know the content of the data, but that it could be recovered. I would like to know how ...
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54 views

Authenticated encryption with Enc-Sign-Mac

I've given a CPA secure private key encryption scheme, an unforgeable private key MAC scheme and an unforgeable public key signature scheme. I want to combine them to protect confidentiality, ...
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37 views

Can I open a file in plaintext (already decrypt) but the cipher doesn't change?

I want to create an app that encrypts a file and saves it to the Dropbox. Thus, I open and edit this file, I want the file is already decrypted, but the encrypted file that stored in Dropbox still in ...
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200 views

I homebrewed an algorithm. Is it secure?

This is a bit of a cross-posted question which I first asked at StackOverflow, however I was not satisfied with stackoverflow, so I came here for an in depth answer. I, as they say, "rolled my own ...
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Finding sum of two encrypted numbers

Let's consider such process: Two emitents emit two (integer) secret numbers independently They encrypt (encode) these number in such a way that no-one (except emitent) can decode these numbers. ...
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SHA encyption (help me) [closed]

OK, so I am a real noob at cryptography stuff and I have a set of files. One is a string that I am trying to decrypt, and the other has this SHA: 4534e95cb5f001719a6119a092459dc826965d60 Can I use ...
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1answer
89 views

Authenticated encryption with Signatures

I've given a CPA secure private key encryption scheme (wich gets to a CCA secure scheme or better to an authenticated encryption scheme, when i combine it with a given MAC) and a unforgeable public ...
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Homomorphic system that allows Hamming distance computation?

How can I work out Hamming distance between two binary vectors securely? I would like to know how I can apply homomorphic techniques here.
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80 views

Combining public key signature schemes and private key encryption

I'm working on my bachelor thesis and I have some questions. I want to combine a CPA-secure private key encryption scheme and some unforgeable public key signature scheme (in my case some sanitizable ...
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1answer
74 views

Is RSA encryption without padding secure with NIST Key Establishment schemes?

NIST SP800-56B standard (addressing IFC-based Key Establishment schemes) defines some key establishment (KE) schemes using the RSASVE primitive in which the common secret $Z$ is encrypted with RSA-EP ...
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28 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 ...
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464 views

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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254 views

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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196 views

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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74 views

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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32 views

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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4answers
179 views

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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73 views

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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47 views

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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Whether this PRG is secure or not

This is the question. Suppose $G$ is a secure PRG with expansion factor $\ell(n) = 2n$ such that $n$ is a security parameter. Is it always the case that, $G'\colon \lbrace 0,1 \rbrace^n \to \lbrace ...
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59 views

Reverse Encryption Algorithm from Decryption code

I have the code for a decryption algorithm but I'm struggling to figure out how to reverse it into the original encryption code. ...
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The internals of bcrypt

I'm attempting to get a better understanding of cryptography and have run into some questions about bcrypt. Bcrypt relies on the blowfish cipher, which is a reversible method of encryption. But ...
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How do I attack an RSA setup where e is even?

As a challenge, we were shown an RSA setup where we have a big $n$ (617 decimal digits), $e=4$, and asked to recover three messages. (However, the messages are padded to the same length as the key ...
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python v.3.4.2 cryptography systems [closed]

does anybody know how to encrypt and decrypt using python3.4 shell cos i was wondering why people have been creating cryptographic lists then inputting them into python. The lists look something ...
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Encryption & decryption of integers using modular multiplicative inverse and extended euclidean algorithm

I'm looking for a neat algorithm, which is capable of encrypting an integer to another integer and decrypting it again AND is secure. When I was in university, my professor showed me an awesome way ...
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Given enough RSA ciphertext, is it possible to determine which key was used?

Given enough RSA ciphertext, is it possible to determine which public key was used to generate the ciphertext? Presume an unknown public key that was used to generate RSA ciphertext, and we have ...
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How is injective, inverse, surjective & oneway related to cryptography?

Just researching cryptography concepts and finding it really hard to absorb them. I would love to know how these functions (injective, inverse, surjective & oneway) are related to cryptography. ...
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256 views

How many possible Enigma machine settings?

I'm trying to calculate the amount of settings the enigma machine has. I have found several sites regarding this topic, but it seems like there are two answers to my question. The first answer is ...
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Is there any benefit to using a randomly chosen replacement strategy on a string before or after encrypting it?

This is more of a mental exercise for me than anything else. I've thought about doing something like this before, mostly to make a broken cipher a little more difficult to decrypt to plain text. I've ...
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SSL Traffic Inspection

Is the firewall decrypted my session? There is an error "Certificate Not Trusted" (Server Certificate changed to Firewall Cyberoam Certificate). Which public Key I got? Is Main server Public Key or ...
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Would a non-deterministic (read: randomized) compression algorithm be crypto-safe?

Would a compression algorithm that randomly shifts stuff around every iteration be TLS/crypto-safe? This randomization would prevent the same byte sequence from appearing twice in a row, thus making ...
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Breaking Homophonic Cipher [project]

This is basically my project. I would be much appreciated if anyone could help me figure out how to do this in an efficient way. This cryptanalysis project consists of a software implementation of ...
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58 views

Using same encryption key in different schemes

Is it safe to encrypt possibly same plaintexts with 2 different algorithms using same secret encryption key? This question is similar to this question except they use 2 keys. More formally: $E_k(m) = ...
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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 ...