# 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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### Perfect secrecy of a crypto system

Suppose we have the following crypto system: $P = C = K = \{0, 1, . . . , n − 1\}$, $E_k(x) = (x + k) \bmod n$ and $D_k(y) = (y − k) \bmod n$. Prove that the crytosystem has perfect secrecy. Perfect ...
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### Key derivation for AES-Encryption key and HMAC

Okay so I have two options for how I would derive two keys for AES encryption and HMAC they are as follows: Run BCrypt on a users passphrase and then use the bouncy castle implementation of HKDF in ...
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### Are there any many to one encryption frameworks available?

I am reasonably new to the cryptography. For my use-case I need a method where in I would need a receiver to accept encrypted messages from a range of senders (each having their own, say, public key). ...
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### Can Diffie-Hellman be scaled up or force-multiplied?

I'm not too familiar with the math involved with the exchange of keys, I've read it over several times, but math isn't my strong point. My understanding is that smart people are hard at work to ...
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### Most efficient conceivable padding mode, and with no padding oracle

When plaintext padding is required, there are various commonly-used padding techniques. It seems the two most used approaches are : Always add at least one byte of padding, and have every byte of ...
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### For calculating the index of coincidence for each sequence

I was learning about the finding the key length reading the following web site... http://practicalcryptography.com/cryptanalysis/stochastic-searching/cryptanalysis-vigenere-cipher/ and I really don't ...
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### Large text file encryption per line

Some background: I receive data in text files of over 16 million records (lines). I need to be able to encrypt the first column in that file so that it cannot be deciphered. This process will be ...
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### Encrypt HDD with keyfile and password and allow backing up the keyfile with secret sharing

I want to: Encrypt my whole HDD with a keyfile and a password (meaning that both are required to decrypt it), Be able to back up pieces of the keyfile in several distant locations using Secret ...
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### Why Distance-128 relation in Plain texts is reflected in Cipher texts

The two text having relation as "\x10\x11" → "\x90\x91" (80+10) will have relation after encryption/decryption also in RC4. Following code clearly describes the problem I am mentioning. ...
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### Can CBC encryption have separate keys for separate blocks of plain text?

Can we have separate key for separate blocks which we get while operating a plain text message using CBC encryption model? If yes, what are it's advantage? Please enlighten me.
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### Encryption of numeric value using playfair

I am studying in CSE and in my recent exam paper, A question was asked as: Construct a playfair cipher for Plaintext: semester5 and key:technology. Generally as we are taught yet, there is no ...
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### Compared to GCM or XTS modes, how secure is H xor R1, E (R2, R1, Message) for confidentiality and integrity?

Let R1 and R2 be (32 byte) random values, and let a H = Hash (R1, R2, Message) be of the same length as each R value. Provided E (R2, R1, Message) is operating in some chaining mode, are there any ...
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### Method to calculating e in RSA

For simplicity I choose two small primes for p and q. p=3 q=11 n=33 Φ(n)=20 Now we need ...
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### Password as it relates to various encryption schemes

Suppose you have 2 drives you want to encrypt using different encryption algorithms, as an example: AES256 and Twofish. I am aware that using the same password for both could potentially weaken ...
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### Intuition for random variables in cryptography

I have a simple question about the use of random variables for encryption schemes, to make sure my intuition is correct. We say $P(K = k)$ to represent the probability that a particular key $k$ is ...
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### Solid summary of what encryption remains strong after recent events [closed]

Following the recent government hacking (and subsequent news and fallout), I'm wondering what crypto-systems remain strong (and why) and what crypto-systems were exploited too heavily to be reliable. ...
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### Curve parameter for hyperelliptic curve cryptography?

RFC5639 defines some curve parameter for Elliptic curve cryptography. Aren't there any curve parameter database for Hyperelliptic curve cryptography? What I can only find was that written in this ...
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### Send a message to an entire group of recipients

I'm attempting to send a message to a group of recipients, through an untrusted intermediary. Each of the recipients will have been invited to the group by someone who already has a trusted public ...
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### How practical is proxy re-encryption for AES?

In proxy re-encryption schemes, a proxy is given special information that allows it to translate a ciphertext under one key into a ciphertext of the same message under a different key. How ...
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### What is the significance of i^Q mod P = 1 and are there any special properties to be aware of?

I'm studying UProve, and one of the fundamental components of this technology is based upon the relationship between i^Q mod P = 1 Lacking a specific name I can call this mathematical ...
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### Request for 1024-bit primes $p$ , subgroup $q$ and subgroup generator $g$

I need to find a prime $p$ of $1024$ bits with a $160$ bit sub group size $q$, such that $q|p-1$ , and $g$ is the generator of the sub group size $q$. I'm looking for the numeric values of $p$ , $q$ ...
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### Does the MixColumns step come before or after AddRoundKey in AES decryption?

I found these images depicting the AES decryption process: In the first image, the MixColumns step comes before the AddRoundKey step, while in the second image, the AddRoundKey will come before ...
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### Which encodings have |encoding key| >> |decoding key|?

I'm looking for an encoding scheme that requires a very large encoding key E (>10MB) and suffices with a relatively small decoding key ...
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### Security Strength of Double Substitution Ciphers

I am wondering why people are using RSA keys when some types of double substitution ciphers seem to be just as secure if not better off. By some types of double substitution ciphers I mean one Which ...
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### Combining secure hashes with insecure hashes?

Assuming I'm a bank which seeks for secure hash functions to use in the process of signing on digital contents. I'd like to explain / prove why using each one of the following hash functions might ...
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### Exponential cipher theory misunderstanding

Say I pick modulus $m=2633$ and key $e=13$ My private key $d$ is $13$ inverse in $\bmod 2632$ which I need to compute $(e,m)$ is my public key that anyone can use to encrypt message for me and then ...
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### Application level encryption and key renewal

I had posted this question on stackoverflow and been asked to move it to crypto. What is your view on this? What is the doability? I have a question related to encrypting data in the database, at the ...
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### Algorithm to rotate values in a predefined manner

I will start with an example. Some beacon like estimote Beacons use something called secure ID. The ID transmitted by the beacon change every 10 minutes autonomously without contacting the server. ...
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### Triple DES with 2 keys

Suppose triple DES is performed by choosing two keys $K_1$ and $K_2$ and computing $C = T (T (T (L, K_1), K_2), K_2)$. How to attack this modified version with a meet-in-the-middle attack, in which ...
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### Determining an encryption key when ciphertext and algorithm are known

I would like to know how I can tell that I have successfully performed an exhaustive search attack on an encrypted message. Here are the conditions: key is 40 bit I am aware of the cipher text and ...
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### How to use OpenSSL command line utility to encrypt data with encrypted key from public key?

I may not be asking the right question. I am fairly new to data encryption. I am currently being sent encrypted data that's stored as follows: [ [keysize] [key encrypted with public key] [ivsize] ...
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### Verifying Without Knowing Key

Say user Bob sends an encrypted message to a server. People can download the message from this server and later get the key directly from Bob. Is it possible for the server to somehow verify that ...
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### Format Preserving Encryption FF1 Samples

NIST published methods for Format-Preserving Encryption and there is a link in the document giving examples for FF1 methods. I am confused by the value of R given in the examples. $R$ is the output ...
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### WPA-PSK authentication without password [closed]

Suppose I have a service in which I allow users to share their WiFi connection. When sharing their connection, users provide their WPA PSK password to my service. Now if somebody wants to use this ...
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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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### 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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### 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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### 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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### 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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### 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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### Is it possible to create a detection oracle for all block cipher modes? — ciphertext-only cryptanalysis

I have made an ECB/CBC detection oracle, and am now trying to make a detection oracle that can differentiate between CBC/CFB/OFB/CTR/etc. I can already tell ECB apart from the others due to this ...
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### List of post quantum cryptography protocols [closed]

What are the post quantum cryptography protocols that have been proposed until now? I know about McEliece cryptosystem, and LWE scheme. What are the others? Can you provide me a list or a website ...
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### Confidentiality then Integrity with different keys

Can anyone describe how we can do what is said in the below sentence which is in Mark Stamp crypto slides (PPTX) on slide number 101 : Can do a little better - about 1.5 “encryptions” The whole ...
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### C implementation of GEA/3 [closed]

Can somebody please point me to an implementation of GEA/3 (an encryption algorithm) in a high-level language (preferably C/C++)? I looked for a while but could only find block diagrams and ...
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### What do associated data and message numbers mean?

I'm reading an article about authenticated encryption and don't understand some inputs to an encryption function. They are associated data, public and secret message numbers. Can you explain me their ...
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### How to create and validate potential grids when attacking a Playfair cipher?

First up: I am not asking you to decypher anything. This question is about attacking a Playfair cipher; more specifically – how to create potential grids when doing so. I'm currently working on a ...
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### Is it possible to encrypt a message with two different keys (or maybe a public key) such that ciphertext will be decrypted with either of the keys? [duplicate]

I have an app that I store sensitive user data which requires user to set a password to login the app and I use this password as key to encrypt the data. Now, I want to add an option to login the app ...
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### Cardholder to Merchant SET Protocol

I have some doubts regarding the SET protocol. Let say the Alice payment information runs through a sha-1 hash function which is a one-way algorithm, irreversible to create a message digest. How do ...