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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Concatenated Key Question - Poly-alphabetic Substitution and Columnar Transposition

I am working on a degree module, and have been tasked with designing an Encryption/Decryption algorithm. I hope to receive some help with a couple of questions, if possible. Apologies if terminology ...
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One cipher to rule them all?

I learned from Dan Boneh's course that many cryptographic primitives (prngs, stream ciphers, hashes, hmac, key derivation functions) can be built from just one a block cipher or PRF. For example, the ...
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How to encrypt an image with logistic chaotic map?

I need to encrypt color images, using logistic chaotic map. Could you please recommend an algorithm for this? All the articles that I've found on the Internet are completely unclear.
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Is pseudo-random letter insertion secure?

Is pseudo-random letter insertion a secure mechanism? I mean by expanding the key or taking two parameters in the encryption function, you select positions in the text at which to insert random ...
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AES - Size of T-Boxes and obtaining T-Box values

In article "A high performance ST-Box based unified AES encryption/decryption architecture on FPGA" (http://www.sciencedirect.com/science/article/pii/S0141933115001945) two 32Kb dual-port BRAMs are ...
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Combining multiple PRGs together

Got some theoretical questions about PRGs to solve (given by lecturer for self-learning, no score involved). Tried to find on the internet but couldn't figure out how to solve them, so I will mention ...
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Is it safe to use the same IV for multiple encryptions in AES CBC mode when you are always encrypting random bytes?

I am generating random bytes (16 or 32 bytes at a time), and I want to encrypt them using a 128 bit AES key in CBC mode. Am I really weakening this horribly if I am reusing the same IV and key each ...
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1answer
71 views

How can public key not reverse encryption if the algorithm is known? [duplicate]

I've been reading about WhatsApp getting "end-to-end" encryption, and when reading about it, I've notice something. If I want to send a message from cell $A$ to cell $B$, since there's a public key, ...
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How secure is AES-256?

The cipher AES-256 is used among other places in SSL/TLS across the Internet. It's considered among the top ciphers. In theory it's not crackable since the combinations of keys are massive. Although ...
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1answer
72 views

Trusted Third Party Cryptanalysis Labs?

There's no doubt that third party cryptanalysis is an essential part of the crypto ecosystem. It's how we know that there's some degree of practical "goodness" to a new algorithm or protocol. Unlike ...
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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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Filling in MD5 input variables

I have a majority of an input string(as well as the total length) and the output for an MD5 hash. Is there a way to calculate the remaining input bytes that I am missing?
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CryptDB data re-encryption and onion layers

From the CryptDB paper , I understoond that the onion layers once decrypted are not re-encrypted. Only columns which are queried infrequently will be re-encrypted to higher onion layers. But if we ...
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1answer
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Is it safe to use PBEWithMD5AndDES?

I'm encrypting some of my (not so much important) files with PBEWithMD5AndDES. Is it a strong method or it can be de-crypt easily without knowing my selected ...
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43 views

Unpredictable value rotation

I have very vey basic skills in cryptography, it's hard for me to explain clearly my problem so I will start with an example. Estimote beacons have a security function called secure UUID, once ...
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1answer
61 views

What are the possible security issues when exporting a plaintext database to a file like this?

Say I have plaintext database with key-value pairs of usernames and passwords. Then I iterate through the database, encrypt the passwords, and write the username and encrypted password pairs to file ...
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Is there something wrong with my decryption using key=9, mod 26?

I am new to cryptography and have started looking at some basic encryption. I have the following question to answer: Decrypt the the following encrypted quotation using ...
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2answers
79 views

How to make the range of modulo $p$ to $[-\frac{p}{2};\frac{p}{2}]$?

I am using NTL (A Library for doing Number Theory) to implement a FHE (Fully Homomorphic Encryption) scheme. In general, the range of modulo p is $[-\frac{p}{2};\frac{p}{2}]$ in FHE scheme. However, ...
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134 views

How to reverse engineer a cryptography algorithm if some input-output pair is known.

I am trying to reverse engineer an unknown encryption algorithm. By this, I mean I dont know what kind of algorithm is used to encrypt the words. But I know some input-output pairs. From this point ...
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80 views

A block cipher whose key changes after each block

I have been reading about various block cipher modes of operation, and all of them seem to treat the block cipher (including it's key and key schedule) as a sort of immutable black box. I would like ...
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1answer
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How SAM modules secure transactions?

As you know SAM Modules are used mainly in the electronic payment industry. Due to the low security of key storing in general storage devices or MCUs, Manufacturers used SAM modules for secure storing ...
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2answers
66 views

How to prove a symmetric encryption scheme provides perfect secrecy?

I learned in class that in order to achieve perfect secrecy, the source of the plaintext $\mathcal{P}$ needs to be independent from the source of the encryption key $\mathcal{K}$. We also learned that ...
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67 views

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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Can you help me understand what a cryptographic “salt” is?

I'm a beginner to cryptography and looking to understand in very simple terms what a cryptographic "salt" is, when I might need to use it, and why I should or should not use it. Can anyone offer me a ...
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Performance of Fully homomorphic encryption VS Paillier encryption in Practice

Consider two schemes both have computation complexity linear to the input size (i.e. number of inputs). One scheme is based on Paillier encryption and the other one is based on fully homomorphic ...
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Are there any crypography schemes which rely on Graph Isomorphism not being in P?

Are there any cryptography schemes having correctness relying on Graph Isomorphism not being in P? If I should ask this question in the CS Theory area, I will migrate it. Thanks.
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If you receive a message with a digital signature, how do you know what verification key to use and the verification algorithm?

Really, I'm asking how do you know who sent it? My confusion has arisen from the following scenario... Problems with Signing-then-encrypting. If Alice digitally signed some data and then encrypted ...
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Big-O Notation: Encryption Algorithms

I am currently completing a dissertation concerning the encryption of data through a variety of cryptographic algorithms. I have spent much time reading journals and papers but as yet have been ...
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1answer
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CCA on PKCS#5 using error feedback

My question is about attacking PKCS#5 with CCA using the error feedback. What we learnt in class about PKCS#5: CBC requires padding to whole block boundary PKCS#5: standard padding If ...
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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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Can error correcting codes be used to guess this plaintext?

I pick a finite set of messages, perhaps the set of integers $M = \lbrace n \in \mathbf{Z} \, : \, 0 \leq n\lt10 \rbrace$, which you are then allowed to encode in any way you want (some form of error ...
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155 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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58 views

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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Asymmetric password encryption - Viable? Which algorithm?

We have an application that requires cleartext passwords for user authentication because of the authentication mechanism in use (RADIUS/CHAP), which unfortunately we cannot change. Since we don't want ...
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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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Why does the recommended key size between symmetric and asymmetric encryption differ greatly?

In various articles it is mentioned that for secure communications, the recommended key sizes are 128-bit key size for symmetric encryption (which makes it $2^{128}$ possible keys?) and 2048-bit key ...
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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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ECDSA vs ECIES vs ECDH

Recently I started studying Elliptic Curve Cryptography and I just loved it. I want to transfer some big data (like 3KB), What is the best method, ECDSA, ECIES, or ECDH (and why)? I am confused, how ...
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11answers
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Should we MAC-then-encrypt or encrypt-then-MAC?

Most of the time, when some data must be encrypted, it must also be protected with a MAC, because encryption protects only against passive attackers. There are some nifty encryption modes which ...
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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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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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1answer
107 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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1answer
70 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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3answers
630 views

Does keeping a public key private or using multiple encryption help?

I recently had a discussion with a friend of mine about cryptography. As we are both no experts, I thought that I could better resolve are dispute here. My friend said that when he used public key ...
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2answers
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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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67 views

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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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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3answers
133 views

Key length requirement in a simple XOR implementation

I don't have much previous experience at all with cryptography, this is pretty much the first time I've tried anything similar. I'm trying to implement an extremely simple XOR encryption system in ...
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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 ...