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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Image sharing without data overhead

The idea is to share $n$ images among $n$ persons so that all images can be reconstructed by someone in possession of all shares. However, there must not be any data overhead (which means the shares ...
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Changing encryption key without revealing the original key

Say that Alice encrypts a $\text{plaintext}$ with $\text{key}_{m}$ and gives the $\text{ciphertext}_m$ to Bob. Alice wants to send several gigabytes of $\text{plaintext}$ to Eve but she is on a mobile ...
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34 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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489 views

What is cryptographic agility?

I keep seeing the term "Cryptographic Agility" referenced. What does it mean? For instance: https://msdn.microsoft.com/en-us/library/windows/desktop/bb204775(v=vs.85).aspx One of the key value ...
4
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1answer
469 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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288 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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36 views

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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1answer
1k views

How does the Blowfish algorithm key initialization work

I'm having some trouble understanding the Blowfish encryption algorithm. From the Wikipedia article... The secret key is then, byte by byte, cycling the key if necessary, XORed with all the P-...
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2answers
426 views

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 ...
3
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3answers
145 views

Is an android encrypted SDcard readable/decryptable easily by a desktop machine?

If I encrypt my SDCard on my android phone using the built-in encryption software, and my phone dies for whatever reason, would I be able to easily by just using the pin/password to access that data ...
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0answers
26 views

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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2answers
75 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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4answers
200 views

How is a message digest decrypted?

Trying to get my head around digital signatures and hit a slight block. The book I am using gives the following information Device A hashes a message to create a message digest Device A encrypts ...
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1answer
101 views

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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1answer
33 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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3answers
831 views

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 ...
0
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1answer
103 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 ...
2
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1answer
99 views

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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1answer
48 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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1answer
131 views

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 ...
3
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1answer
81 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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1answer
49 views

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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1answer
101 views

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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63 views

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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2answers
63 views

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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3answers
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Which of these 3 AES 128 symmetric encrypt/decrypt routines is most secure?

I am developing a symmetric en-/decryption routine written in c# for a database containing user-specific, sensitive information. I have narrowed down the implementation to 3 different approaches, ...
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2answers
61 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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2answers
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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 ...
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3answers
108 views

In an A5/1 stream cipher, why do the registers have a stepping probability of 3/4

I know that the probability of each register to step is 3/4 but I have yet to find an explanation of why. Can anyone explain this to me?
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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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2answers
129 views

Is this method of encryption theoretically unbreakable?

I implemented a Stream Cipher using Cryptographically Secure Random Numbers for the key values. The key stream was as long as the plaintext stream. This key data set won't be reused. Have I met all ...
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3answers
144 views

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 ...
5
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314 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 ...
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1answer
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Knowing the key, how do I decrypt the affine cipher?

I have an encryption function $$E(p) = (ap + b) \mod{26}$$ where the parameters are $a=7$, $b = 10$, and $p$ is the plaintext letter. I was asked to decrypt the ciphertext ...
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1answer
60 views

Number of shifts in DES key schedule

In DES key schedule some rounds use one left shift while others use two left shifts. What is the reason behind this?
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20 views

Is there any difference between a one-time pad and a Vigenère cipher with a long key? [duplicate]

I've been browsing Wikipedia and stumbled on the article for the Vigenère cipher. I realized after seeing the example that it's quite similar to the one time pad, except with a short key repeated as ...
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22 views

Confidentiality then Integrity with different keys [duplicate]

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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0answers
76 views

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 ...
0
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0answers
41 views

Does encrypting with MGF1/SHA-512/1024-bit seed equal to a 1024-bit key block cipher?

Suppose: Alice uses SHA-512 with MGF1(as in PKCS#1 V2) and a 1024-bit random seed to generate a mask, XORs the mask with a message(M), gets a cipher text (CT), and sends the CT to her old friend ...
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0answers
11 views

Calculating inverse of transposition key cipher [duplicate]

I need some help on transposition cryptography. If I'm given the encoding key to a transposition cipher, how do I get the decoding key for it? I tried googling but couldn't find any steps on the ...
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1answer
46 views

How to test an encryption against different attacks [closed]

For the last while I have been reading up on cryptography and the different kinds of methods for encryption (public key, blocks, etc) and the attacks against them. This got me wondering how to ...
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1answer
57 views

Public-key encryption with associated data

In the symmetric-key world, we have authenticated encryption with associated data (AEAD). I'm looking for something similar, but for public-key encryption: public-key encryption with associated data (...
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3answers
1k views

How is the One Time Pad (OTP) perfectly secure?

The Wikipedia entry on One Time Pads (OTPs) states that if this cipher is used properly; ie, the keys are truly random and each "part" of the key is independent of every other "part", it's uncrackable,...
3
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1answer
138 views

Relationship between exponent and modulus in RSA (as RSA properties as listed in X.509)

In one of my assignments, I had the following question (Please read on. Not a homework assignment :) ): X.509 (1998 version) lists properties that RSA keys must satisfy to be secure. One such ...
2
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3answers
166 views

How to disguise ciphertext

If I want to have a secret conversation, then I can encrypt it (with OTR etc). However, since big brother watches all communication, sending encrypted data will likely raise flags. Does anyone know of ...
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2answers
106 views

RSA algorithm private key extraction

Decrypting messages can be done by using the following formula: $$M = C^d \mod n$$ Where $M$ is the decrypted message, $C$ is the encrypted message and $d$ is the private key Theoretically speaking,...
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1answer
401 views

How do you test the security of your cipher?

I got asked this question and I didn't know what to answer. How do you test the security of your cipher? What comes to my mind now would be to test it with famous attacks: padding attacks, ...
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1answer
125 views

Encrypting passwords

I am using Android's keystore to generate a key which is protected by fingerprint authentication. This key can be used to encrypt any secrets. In my case, I want to encrypt a user password (which is ...
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3answers
735 views

AES CTR with similar IVs and same key

Let's say there is a piece of software that uses AES CTR to encrypt different messages using the same key but with slightly different IVs. So for example, a 16 byte IV, the 2nd 8 bytes are always ...
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1answer
67 views

Hash + Salt v. Hash + Encryption

I was wondering if using a salt with a hash is more effective than hashing and encrypting your hash.