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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How to construct the blind factors in practice?

I'm Implementing a protocol that uses masking techniques (or blinding factors), so we can mask a value $y_0$ as $m_0=y_0 \cdot r_0$ where $y_0 \in \mathbb{Z}_p$ and $r_0 \stackrel {R}\leftarrow ...
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19 views

Using ECB as encryption mode, but encrypted messages are unique

As I understand, ECB should not be used as encryption mode unless you are encrypting single blocks of data which are always unique and only are encrypted once. I have a collection of ids represented ...
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1answer
60 views

AES process candidates implementations and usages

There were fifteen candidates in the AES selection and I suppose that Rijndael wasn't the single good algorithm. I know that Camellia is an evolution of E2 candidate and can be used as symetric ...
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53 views

Which one these alternatives using authentication and encryption will solve this multiple-user database problem?

Which one these alternatives using authentication and encryption will solve this multiple-user database problem ? I'm trying to understand the field of cryptography, so I've started reading a ...
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117 views

Decrypting an encrypted text file

I have encrypted a text file which contains few lines of text. After performing the encryption process, the encrypted text is saved into a text file. The Cipher text for the word "Inform" is "24 102 ...
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1answer
71 views

How does the certificate authority generate a signature F?

E=encrypt(K,M) - is message M encrypted with key K gives encrypted text E M=decrypt(K,E) - is encrypted text E decrypted with key K gives message M KCA−pub,KCA−priv - is the private-public key pair ...
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1answer
31 views

DSA: Authentication and assurance of authorized parties

When dealing with Asymmetric cryptographic algorithms, usually the sender of the critical data asks the listener for a Public Key for encrypting the data and sending them. This is while the private ...
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1answer
53 views

If the text was compressed before using traditional cryptography, how much difficulty increases for frequency analysis attack?

Traditional encryption is weak and no longer be used. They can be easily broken by using frequency analysis is a well-known fact. But, the frequency analysis often depends on the number of captured ...
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1answer
60 views

plaintext distribution ,perfect secrecy cryptosystem

I have been trying to solve the next problem: let pi be a perfect secrecy cryptosystem with specific plaintext probability distribution. How to prove pi will have perfect secrecy for all other ...
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112 views

Why is there an extra block when encrypting?

I am passing input data 20 bytes long and java AES-CBC returns 48 bytes instead of 32 which is what I think it should output because of padding. My key is 16 bytes long. ...
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1answer
90 views

Cryptography system that limits the length of the encypted message

I have two devices which communicate via sms. This communication should now be encrypted. The devices can only send messages with the lenght of 160 characters. So i am looking for an encryption ...
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72 views

FEAL-4 Fk Function 4 Rounds

As I understood in FEAL-4 it needs 4 pair of round keys. Which means that we need to launch Fk function 4 times. My problem occurs starting the 2nd round. At the first round we have the original 64 ...
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simple encryption scheme turns out to be “somewhat homomorphic”

In the paper Fully Homomorphic Encryption over the Integers in the introduction: How do I calculate $r$ and $q$ of this equation in the picture? $r \approx 2^{\sqrt{\eta}}$ and $q \approx ...
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1answer
92 views

Is there an encryption that is only reversible with a key?

I'm thinking about man-in-the-middle attacks during a website login, and started wondering about reversible encryption. What I'm imagining is an encryption that takes input ...
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1answer
80 views

Unbreakable code and mathematical impossibility

Is an unbreakable code mathematically possible , considering a code with finite number of characters but has infinite combinations , using brute force is it not compulsory that the correct code be ...
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501 views

How compared encryption algorithm in terms of efficiency

I want to compare two cryptographic algorithms. The first algorithm is RSA, and second algorithm is ElGamal elliptic curve cryptography. Now, I’m looking for a way to compare the speed of the two ...
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210 views

Is TOTP or a timestamp encryption a better timestamp-based authentication token system?

Are there advantages to using TOTP over encrypting a timestamp with a shared secret, in cases where the readability or ease of typing the token are not important?
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6 views

public key for encrypting and both private and group key for decrypting

A document is ecncrypted using publickey within a group(consists of many users with single public key and individual private key),then how to decrypt the document by using both public key and private ...
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30 views

prevent padding oracle attack on key exchange process

I found in my searches that the padding oracle attack can be used against the RSA with PKCS1PAdding or OAEP padding, and I used this algorithm for a symmetric key exchange. How can I prevent a padding ...
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38 views

Enigma algorithm Question about the Ringstellung

This might be a stupid question but I need to implement the Enigma algorithm and I don't fully understand how it works. I've googled the subject and I am confused about what the Ringstellung is and ...
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58 views

Rabin cryptosystem with 1 mod 4

We have p and q which are distinct primes congruent to 1 mod 4. Then we have n = p*q. Do you know any algorith for calculating square roots for the decryption in this case? I'm asking for some ...
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21 views

Does it make sense to have multiple values of authentication and cipher offsets while encrypting a packet?

Consider a packet with N segments. cofsset(cipher offset - from where one must cipher) lies in arbitrary Segment "A". aoffset (authentication offset - from where one must authenticate) lies in ...
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23 views

Device intercommunication with commands

I want to create a smart house project, and in that i bought some simple RF modules. Those modules don't support crypto out of the box but i want to connect them to a device that i would program to ...
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47 views

common ways / methods to try to break a SP network

I have a very little cryptography background (but a relatively solid maths background) so my below question is very general. Basically I have been given a SP network with an output to reverse. I ...
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Composition of non-perfect encryption keys

Definition 1: A key $k$ is called perfect if it is uniformly distributed from the adversary's point of view; a key $k$ is called $ε$-perfect, if its distribution has an $ε$ trace (statistical) ...
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Requested to encrypt data with AES256, digital certification, timestamped

at my job we have been tasked by gov to encrypt some data we send to them. The "law" says we have to do the title above, but they only need us to do the AES256 thing because the data is not really ...
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43 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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27 views

Transport SA bundled inside a tunnel with encryption applied before authentication?

For IPsec I am considering different formats of ESP encryption and authentication. I am not sure what happens with "Transport SA bundled inside a tunnel with encryption applied before ...
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20 views

Looking for an adjustable compute bound decryption function

I'm looking for a way to decrypt data, but make it require varying amounts of CPU power to do so. Maybe this could be illustrated as e(m) = m' and ...
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90 views

Substitution-permutation network

Can anyone in 6th grade English explain the steps in the Substitution-permutation network algorithm or just point a link that does so? (which is included in many of the top modern algorithms) ...
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57 views

How does double-encryption work with a client server model

With mobile applications like Accompli (now the base for the Android Outlook application), credentials are stored. Reading from the Accompli website: Each user’s credentials are double-encrypted ...
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Encryption - How to find $\sigma$?

Alice communicates with Bill using an encryption system of type Feistel. Specifically, each block has a length of 128 bits, the algorithm has 4 rounds and the common secret key of Alice and Bill is ...
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55 views

compression with codebook and Cryptography

a question about the difference between code book based compression method and key based cryptography. As I know Crypto != Compression. The Shannon said Crypto is try to reduce the information of ...
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Data anonymization and search with wild-cards

Broadcast encryption technique proposed by Water et al. http://www.slideserve.com/nairi/revocation-systems-with-very-small-private-keys takes a leap from earlier schemes as it provides smaller user ...
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74 views

How does multi platform encrypted cloud storage work?

I'm really interested in end-to-end encrypted cloud storage and couldn't find out how following scenario could work: A user of a cloud provider which provides zero-knowledge-authentication (like for ...
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68 views

RSA public key exponent generation confusion

Quote from Wiki: $e$ having a short bit-length and small Hamming weight results in more efficient encryption — most commonly $2^{16} + 1 = 65537$. However, much smaller values of $e$ (such as $3$) ...
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221 views

Public key encryption and big files with NaCL

I am trying to encrypt big files using NaCL (actually PyNaCL) - see http://nacl.cr.yp.to/box.html After reading some docs, I came up with this prototype : Bob wants to send a big file to Sarah. They ...
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how can I change representation of point to Jacobian coordinates in Edward's Curve

I want to simulate this algorithm but I want to change it's output to Jacobian coordinates. what should I do ? In the other way how can we change extended homogeneous coordinates to Jacobian ...
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75 views

RSA OAEP: prevention of partial decryption of ciphertexts

I'm trying to understand RSA encryption (as a beginner in cryptography). go on this wiki page http://en.wikipedia.org/wiki/Optimal_asymmetric_encryption_padding scroll down to the 2 numbered points: ...
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156 views

Mifare Classic and crypto1 algorithm

Mifare's Crypto1 algorithm uses a 48-bit LFSR. What does the 48-bit LFSR do exactly ?
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54 views

How can I calculate the size of an encryption key?

I have encryption algorithm that has two variables are used as encryption key. How can I calculate the size of the encryption key. I will show an example of what the variables can be: ...
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Do OpenPGP SmartCards have the same or better security than an air-gapped machine?

Are OpenPGP SmartCards, such as the OpenPGP SmartCard V2, suitable enough to have secure communications? Meaning, if I connect my smart card to my Mac which is connected to the internet and always ...
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52 views

symmetric encryption A5/1 and A5/2 algorithms

where does the key (Kc) used to generate the keystream comes from and also where does the 22bits counter comes from
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71 views

Public key encryption without ciphertext expansion

Say I have a database column that is defined as VARCHAR(255) that stores names. I can assume that names can be up to 255 chars. I need a public key encryption so that I can replace names with their ...
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84 views

Need help solving a shift cipher problem?

A three letter alphabet {a, b, c} has probabilities p(a) = .5 and p(b) = p(c) = .25. A shift cipher is applied to pairs of letters. More precisely: plaintexts consist of two-letter sequences of ...
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64 views

Don't Understand these Parameters

I don't understand section 3 of the paper Fully Homomorphic Encryption over the Integers. How can one calculate these paramters and make these equations in pictures into code?
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153 views

fuzzy commitment implemenation to make secure biometric template

I want implement some ideas from an article that is about making secure biometric templates using fuzzy commitment and fuzzy vault. I need to implement just the fuzzy commitment (fuzzy commitment is a ...
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241 views

Blum-Blum-Shub Cryptosystem

I am given $N$, which is Bob's encryption key. I was able to successfully factor $N$ into $N=p*q$. Alice encrypts a messages for bob and sends $a = [1,1,1,0,0,0,1,0,1,1,0,...]$ $b = 1545164156...$ ...
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A software for test and performance analysis of cryptographic algorithms

I'm new to cryptography and I have been assigned at college to do a comparison study between AES, DES, RC6 and SERPENT ciphers. Is there any graphical software than can help me analyze speed and ...
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encryption system ElGamal

Construct an encryption system ElGamal at the group $\mathbb{Z}_{19}^{\star}$. As base, we can use $g=\overline{2}$, that generates the group. Describe the construction of a pair private/public key ...