# 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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### 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 ...
80 views

### Can we use merely permutation to hide a message?

This question is related to this: When all shares of a secret are given to adversary as a permuted matrix I think the below question is a simplified version of that. Assume we have a 40-bit ...
19 views

### Security issues with self encryption? [duplicate]

I'm thinking about the scenario of using a set of (potentially untrusted) hosts to store (potentially private) files. Think something like distributed backup where you contribute some disk space and ...
105 views

### Is this a good communication scheme?

I'm writing a wrapper for a chat program to allow for end-to-end encryption. I'm using Python and PyCrypto to accomplish this. I'd like to use a well known library to do this, but to my knowledge, ...
133 views

### history of non secret cryptograph

Prior to the discovery of any specific public-key schemes, such as RSA, an existence proof was developed whose purpose was to demonstrate that public-key encryption is possible in theory. Consider ...
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### Finding a secret cipher given the key and known plaintext?

Let $x,y,k$ be plain text, cipher text and key respectively. Also suppose $\operatorname{Enc}$ is the algorithm of encryption for block cipher with size $n$. So we have $$\operatorname{Enc}_k(x)=y$$ ...
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### Encryption that could have multiple decryption key

The title looks strange but it is to deal with this situation. The data we have should only be accessible by our end user and data administrators, not anyone else. Ideally, each user should have ...
93 views

### How to correctly encrypt data with proper authentication using AES-256-CBC in php?

I have been using the openssl function for encrypting data with AES-256-CBC in php. I have been able to encrypt it using an unique IV (by generating with openssl_random_pseudo_bytes)for each new ...
328 views

### Which cryptography technique does not increase the size of the plain data?

I want to encrypt some data(text/voice/video) but it is essential that the size of the cipher data remains the same as the plain data. Which techniques can I use, and how secure are these techniques ...
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### Full encryption of IDs, partial decryption with customer specific key

I am looking for a "partial" encryption/decryption algorithm. Let's say I am encrypting the following List of IDs (long values) $[1,2,3,4]$ (with a secret key) to an encrypted string $e$, I would ...
108 views

### Using e-ID Number for Encryption and Digital Signing

I want to use e-ID number for performing Encryption/Decryption and Digital Signing - and in order to do so, I've opted a PGP-oriented approach which goes a bit like this. Generating PGP key-pair ...
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### If you use an AES key just once, do you need to use IV, and/or pad the message? [duplicate]

I am developing an application that is going to use AES encryption. Since it is going to use a different key for every message encrypted... Would it be secure to use a constant IV? (i.e null bytes) ...
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### Understanding the cryptography used in a file [closed]

I use a software that stores a raw binary file with information, and exports it to a text file. I have access to the data in the original binary file. You can find a sample of the contents of the raw ...
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### Non-numeric Diffie-Hellman?

It may seem that this is a programming question, but I just need advice on the cryptography side of the question. I want to implement the Diffie-Hellman key exchange algorithm on iOS (since no free ...
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Is there any difference in adding the plain text and key vs using xor instead(apart from the performance improvements)?
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### Recommendation for lightweight algorithm for partial message encryption

I have designed a specific client and server program, which sends a file from client to server in 32k chunks. I want to encrypt only part of the data. More specifically: in each 32k chunk passing ...
444 views

### Should AES.decrypt(ct, wrong_key) return blank or wrong result?

I am trying to use AES as cipher for an application I am building. I am using a JavaScript library (https://code.google.com/p/crypto-js/) to perform encryption and decryption with AES. When I ...
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### Encryption scheme like RSA where encryption is the inverse of decryption

In RSA, it is basically equivalent to use the private key $d$ to encrypt as it is to use the public key $e$ to encrypt. They are exactly inverses: $e=d^{-1}$. I need to know, are there other public ...
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### Which ciphers produce random ciphertext?

I already know AES produces a "random" output. 5e4e6440826d6afc4535fbf078455f791159701a9df624ddd4e4dda84523b6a7 Its ciphertext doesn't follow a pattern and is ...
130 views

### Is it safe to use XOR to encrypt data key using master key

I am implementing a hierarchical key system with a randomly generated master key and many randomly generated data keys that should be encrypted using the master key. I am wondering what the best way ...
2k views

### Are there any advantages in using proprietary encryption?

Proprietary software generally relies on the fact that in keeping the encryption algorithm private, it gets an extra layer of security implying "Security through Obscurity." Obviously this phrase has ...
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### Algebraic relationship between Original Key and Sub Key of DES

Does there exist any sorts of algebraic relationship between Original and Sub Key of DES? I understand that by solving K-Maps of 64-bit Input/48-bit Output, I can get 16 algebraic relationships ...
292 views

### Does frequent key change weaken encryption?

Following scenario: We are using OTR for communication between Alice and Bob which means after each successfull message exchange a re-keying happens for both parties leading to new AES-keys for the ...
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### Why gcd(r,(p-1)/r) needs to be 1 in benaloh cryptosystem

I recently discovered the benaloh cryptosystem. I am working with the system as it is discribed in the following link: https://en.wikipedia.org/wiki/Benaloh_cryptosystem However I need some help in ...
72 views

### 4 x E = D in Simplified AES how it's possible?

Can anyone explain how it's possible through hexadecimal or Binary 4 x E= D
116 views

### Can somebody help me understand RC4 Spritz? (Three Questions)

So ever since I first took a stab at understanding stream Ciphers, not one stood out more than RC4, because it's so fantastically simple. As most people reading this will know, with its fantastic ...
110 views

### Example of FHEI scheme?

I am reading this paper Toward Secure Multikeyword Top-k Retrieval over Encrypted Cloud Data. I am trying to work out an example of the FHEI (Fully homomorphic Encryption over Integers) scheme ...
278 views

### Affine Cipher over an Affine cipher

I would like to know your view about the title, encrypting a plain text with an affine cipher then encrypting that ciphertext once more using the same cipher, but of course different keys. Would it be ...
235 views

### Should I use RSA encryption since RSA is said to be broken by NSA? [closed]

I am developing a simple web app that uses asymmetric encryption, but I am not sure whether to chose RSA for the reasons mentioned above. What are your suggestions? Also if I decided to go with RSA ...
97 views

### Generating a key to use with AES

I'm going paperless, and I want to encrypt the documents that I scan. I'd like to use CommonCrypto to perform AES-XTS encryption on each file. I'm a software engineer, and I like the idea of being ...
145 views

### Can a book cipher be cracked without key?

Book cipher works this way : Choose a reference book. For each word find its position in the book. replace each word by its coordinates (ie: 2,3,4 = page 2, 3rd line, 4th word). How would ...
60 views

### Does a “commutative” asymmetric system exist?

Completely crypto noob here. I'm looking for a cryptosystem made of a func f + key1 + key2 such that they satisfy: g(f(msg, key1),key2)=msg g(f(msg, key2),key1)=msg key1 != key2 Does such a ...
70 views

### PBC library: group of composite order for pairing operation

How to generate composite order group using PBC library? With PBC library, element_init_G1(g,pairing) statement creates element $g$ for group of prime order. I want ...
63 views

### Encryption used in a commercial software product [closed]

I found (through some reverse-engineering) that the following encryption scheme is used in a commercial software that is quite widely used in Germany (Security by obscurity at its best). I have the ...
385 views

### Need for salt with IV

I have mainly referred to this question. Definitely in case of using a salt, IV has a use of adding randomisation to each and every key. But isn't it redundant in case of using an IV to use a salt? ...
63 views

### Proven secure scheme under random oracle

Currently I am trying to understand random oracle model in order to make a small presentation about it but I seem to be very confused about it. Since it's an hypothetical model without a real life ...
243 views

### Plain text size limits for AES-GCM mode just 64GB?

Based on NIST SP 800-38D section 5.2.1.1, it seems that the maximum length of plaintext is 2^39-256 bits ~ 64 GB. We've got 100+GB files in genomics that need to be GCM encrypted so are concerned ...
67 views

### What can I do to improve my encyption method [closed]

I'm new to cryptography and I want to learn more. For me, the best way to learn about something that I have no experience with is to experiment and I've coded a very basic approach to a simple ...
33 views

### Creating a custom 2 way encryption class [closed]

I am trying to make a simple 2 way encryption function that currently uses a substitute cipher for the encryption and an inverse substitution for the decryption. I want to move away from this ...
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### How to calculate d in RSA for my number with this [duplicate]

I took the p&q value as 61 & 53 and n=3233 e=17 d=? How to find it? Plz help me...
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### Do we have anyway of knowing if avoiding self-permutation in RC4 makes it any stronger?

OK, so lots of questions get asked about RC4 but I want to make mine specific and hopefully answerable. RC4 Design as I'm sure anyone reading this knows, uses self permutation in stage 1 of the KSA. ...
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### What is the difference between MACTripleDES and TripleDES?

I was asked to encrypt/decrypt a string using MACTripleDES. Is there any difference between MACTripleDES and TripleDES? If, where exactly is the difference between both?
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### Proof that a hash matches an encrypted file

Assume that Alice has a file $F$ which she is going to send, in encrypted form to Bob. Alice possesses $F$ and an encryption key $K$. She sends to Bob the encryption of $F$ using $K$, $E(F,K)$ as ...
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### Which crytographic standard were RC5, CAST5 and Blowfish based on? [closed]

Which crytographic standard were RC5, CAST5 and Blowfish based on? A. AES B. RC2 C. 3DES D. DES
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### Proof that perfect privacy implies that the number of keys is at least the number of messages

I was reading a proof to the statement: Perfect privacy implies that $|K| = |M|$ where I am pretty sure that $K$ is the set of keys and $M$ is the set of messages. The proof is the following, ...
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### Convert messages to elliptic curve points [duplicate]

Let $E$ be an elliptic curve; $\alpha,\beta$ two points of $E$; and $a$ a private key such that $\beta=a\cdot\alpha$. We choose random integer $k$ and plain text $x\in E$. Encryption and decryption ...
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### K friedman - two texts explanation

I have a question, I read the k friedman test to determine the period of a vigenere cipher text, and I understand something like this: Friedman's K test tries to find out what period of the cipher by ...
126 views

### Is there an asymmetric encryption algorithm where the public key cannot be derived from the private key

Is there an encryption algorithm that will produce a public key and a private key such that the public key cannot be generated using the private key. For example, if the private key is compromised ...