Encryption is the process of transforming plaintext using a cipher to make it unreadable to anyone except those possessing the key.

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Secure encrypt-then-sign with RSA

I understand that when you want to encrypt and sign data with RSA the generally recommended approach is sign-then-encrypt. However, I have encrypted data that I need to sign, to prove the author of ...
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105 views

Is OAEP reversible?

Given nothing more than some integer $m =$ OAEP($M$), is it possible to recover the original plaintext $M$? In other words, without being given the hash functions or the random string used for ...
3
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131 views

implementing long term archive encryption

Let's say I want to create private archives for the long term (e.g. more than 30 ). The archives' sizes could be anywhere from 1 GB to 30 GB. As far as I understand I could go down two ways: The ...
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1answer
2k views

repeating-key xor and hamming distance

I read that to break repeating-key xor you can do the following: try a keysize $n$ and compute the hamming distance between the first $n$ bits of the encrypted string and the bits $n+1$ to $2n$ of the ...
4
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1answer
176 views

Combining AEAD with RSA

'Hybrid' encryption, where we combine symmetric encryption with public-key cryptography, is pretty 'tried and tested'. To summarise, we generate a symmetric key and encrypt it using RSA. We would ...
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2answers
143 views

GPG and PAR2 error correction data from the plain archive, will it compromise security?

I have the following scenario: Archives compressed with 7z, hundreds of MiB in size GPG to encrypt the archives (binary, without ASCII armor) PAR2 to create error correction data Question 1. ...
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2answers
394 views

Keys required for cryptography

I am reading an article on cryptography at following location: http://www.entrust.com/resources/pdf/cryptointro.pdf Historically, encryption systems used what is known as symmetric cryptography. ...
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0answers
141 views

How can I prove that this encryption scheme from a random oracle is secure?

I am reading this example: A random oracle is an ideal object. What makes a random oracle convenient for proofs is the part about knowing nothing on the output for a given input if you do not ...
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2answers
199 views

ElGamal: Generation of “g” value?

I haven't been able to find a clear explanation on this (and I'm probably just confused in general). I have the following parameters of ElGamal signatures: $p$ = safe prime $q = (p-1)/2$ $g$ = an ...
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1answer
88 views

Why unit vectors should be encrypted bit per bit in that case?

At this work at section $2.2$ concerning a possible application for the BGN cryposystem the author points out that if you want to encrypt a unit vector $\overrightarrow{u_l}$ of size $l$ then the ...
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3answers
174 views

EC equivalent for RSA-OAEP

I have some questions regarding aforementioned subject: Is there a EC equivalent of RSA-OAEP key transport/encryption algorithm ? Is ECIES-KEM sufficient ?
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1answer
165 views

ECKS-PS algorithm: searching in encrypted data; bilinear maps

I have found an encryption algorithm named ECKS-PS (published in the paper Efficient conjunctive keyword search on encrypted data storage system) that allows an user to search in encrypted data. All ...
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3answers
205 views

Ciphers in CBC mode reveal place of change in plaintext

Theoretically, when using a symmetric block cipher in CBC mode, the current block is dependent on the previous block. Suppose one plaintext is encrypted using CBC, and then one bit of it is changed, ...
2
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1answer
89 views

Why constrain the message lengths in indistinguishability in the presence of an eavesdropper?

I need your help with a very basic concept in cryptography which I can't understand/prove on my own. I'm trying to prove and understand why, under "indistinguishability in the presence of an ...
2
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2answers
320 views

How can mega store my login details and still be secure?

I understand how Mega's encryption works. For a quick summary of all those in the future looking for an answer on this... here is how it works: Upon first signing up for an account you make a ...
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1answer
521 views

What's the difference between Trapdoor Functions and Encryption Functions?

From Wikipedia: A trapdoor function is a function that is easy to compute in one direction, yet believed to be difficult to compute in the opposite direction (finding its inverse) without ...
4
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1answer
323 views

Client and server using same SSL certificate - any issues?

I'm working on software where multiple components will communicate with each other using SSL. There would be one central component acting as a server, which would also require the clients to present ...
5
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1answer
125 views

Using encryption schemes for identification

I've been researching how to implement a post-quantum SSL-like connection authentication, especially correct identification&authentization of the server/client. Because good post-quantum digital ...
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2answers
417 views

Can two rc4 encoded messages be XORed and decrypted if encrypted with the same key?

If I have the following: E1 = RC4(M1, K); E2 = RC4(M2, K); If two different messages M1 and M2 are encrypted with the same key, K, can the key be recovered by ...
2
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2answers
252 views

Assymetric 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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1answer
124 views

In which disciplinary category can cryptography be put?

Is it a multi-disciplinary, inter-disciplinary, cross-disciplinary, or maybe even trans-disciplinary? What are the basis to describe each kind? I mean, how can we infer by which disciplinary field we ...
3
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1answer
252 views

How to compute the dot product on encrypted values?

Is there a practical homomorphic encryption scheme that can give reasonable execution time results in computing a dot product: $$a_1*b_1 + a_2*b_2 +a_3*b_3 +\ldots+ a_n*b_n$$ I imagine the scheme will ...
0
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1answer
157 views

Encrypting and Decrypting a 19-digits long BigInteger

How can I take a maximum 19-digits long BigInteger and encrypt it with the following rules: The result must be based on digits and lower-case English letters ...
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2answers
442 views

Security of Deterministic Encryption Scheme

A deterministic encryption scheme is a cryptosystem which always produces the same ciphertext for a given plaintext and key, even over separate executions of the encryption algorithm. Although we ...
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1answer
428 views

How would one crack a weak but unknown encryption protocol?

I asked a question on security.stackexchange, but was told it would be a better fit here: http://security.stackexchange.com/questions/32779/how-would-one-crack-a-weak-but-unknown-encryption-protocol ...
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1answer
148 views

Solving congruences using PARI

I'm having trouble finding info in the docs about how to solve a system of congruences. The closest I can find is 'matsolvemod' in here: ...
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1answer
1k views

Low Public Exponent Attack for RSA

I'm having trouble understanding the algorithm for finding the original message $m$, when there is a small public exponent. Here is the example I'm trying to follow (you can also read it in the 'Low ...
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1answer
1k views

Is AES-256 a post-quantum secure cipher or not?

We know Grover's algorithm speedup brute-force attacks two time faster in block ciphers (e.g brute-forcing 128 bit keys take $2^{64}$ operations not $2^{128}$). That explains why we are using 256 bit ...
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2answers
295 views

Strong encryption done by hand [duplicate]

One of the distinguishing features of a good encryption algorithm, is that it is easy to encrypt, and hard to crack. Are there any that are easy enough for average folk to remember, and calculate by ...
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0answers
64 views

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 ...
2
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1answer
269 views

Encrypting many small messages (log-lines)

What would be the best way of encrypting small mesasages to be stored in encrypted form? (This sounds like somthing a textbook would cover, but I haven't found any references). Let's say I have many ...
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2answers
945 views

Would a “Triple AES” (in the sense of how Triple Des works) serve for a dramatic increase in safety?

The system requires to be as paranoid as possible regarding security. One of the few contemplated changes to the current design is to use multiple encryption. First proposal was to use Serpent on top ...
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3answers
267 views

Is there a way to use Shamir Secret Sharing with updatable data?

I want to divide a system that maintains these properties, based on Shamir's Secret Sharing: A secret key is split up to N pieces, where T of them are enough to reconstruct the key. The original key ...
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2answers
241 views

Security of tokenization of plain text conversations - cryptanalysis

I came across a marketing video here. They claim to perform AES encryption and tokenization of sensitive data, at the corporate gateway, before it leaves the company firewall destined for the public ...
3
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1answer
449 views

XOR cipher for encrypting compiled C code

I'm exploring ways of encrypting Intel hex files we send to customers for flashing onto an embedded device. The embedded processor itself has a built-in mechanism that prevents anyone from reading the ...
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3answers
612 views

Is this encryption algorithm build from MD5 secure?

I'm being asked to use an encryption algorithm in my code, and besides the fact that I'm sure there will be implementation faults that lead to vulnerabilities, I also have concerns about the algorithm ...
2
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1answer
186 views

Can you help me understand how RC4-52 is done using pen-and-paper?

I've played a lot with VIC and enjoy its complexity and effectiveness as a field cipher. However, RC4 has caught my attention lately and I've read there is a RC4-52 variant that can be done by hand. ...
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1answer
731 views

GPG vs PGP vs OpenSSH and management of them

What is the main difference of the three? Can I use only one of them for everything (e.g. GPG for SSH authentication) If I encrypt my private key with a pass-phrase, is it strong enough so that if ...
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2answers
189 views

Zero-Knowledge Challenge-Responce Protocol

Good day to everyone. I am trying to implement an e voting system (just for reference -it is not important though-it is described at the Internet Voting Protocol Based on Improved Implicit Security ...
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2answers
145 views

Is it safe for the ChaCha8 nonce to be deterministic?

ChaCha8 takes a 8 byte nonce (or IV) that should not be the same twice for the same key. Generating this nonce randomly makes me very very nervous for collisions. Is it safe to generate this nonce ...
9
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1answer
2k views

Why is CAMELLIA suddenly so widely used?

When nowadays I point my browser to https sites, the cipher that is on most occasions used is Camellia. My browsers (Chrome and Firefox) seem to prefer it, even when AES is available. Is that not ...
4
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1answer
262 views

Question about why RSA is hard to attack

I think I understand why RSA is hard to attack but I'd like to get clarification if I actually do. Assume there are two people, Alice and Bob, who are attempting to communicate privately but that we ...
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4answers
263 views

Bad/Crackable Encryption Example?

I've been tasked with building up some security exercises (basic CTF training kind of stuff) for work. This should contain a bit of crypto, but my knowledge in this space has been limited to using the ...
3
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3answers
295 views

Why do we assume un-security of communication channel on every cryptography system

While reading about a few cryptographic systems, I noticed that we always assume the communication channel is not secured. Why is this assumption made? And, why the effort is being put into designing ...
5
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1answer
216 views

Low complexity implementation of a small blocksize cipher (< 64 bit)

Searching for "small blocksize cipher" finds a number of discussions on the topic, mostly refering to FPE. This one in particular suggests using AES as the round function of a Feistel network. The ...
2
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1answer
527 views

How to break AES CBC with PKCS#5 padding?

If I have a string encoded with AES CBC with PKCS#5 padding, how can one possibly decrypt/crack it? What are the approaches that one can take to break its security?
18
votes
1answer
794 views

Selective format-compliant JPEG encryption?

I am working towards building a format-compliant encryption system for pictures. The aim of it is to be able to obscure specific areas of a picture (i.e. faces, car license numbers...) while keeping ...
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1answer
130 views

ASCII Message in TV show? [closed]

So I was watching a popular series tonight (Person Of Interest) when suddenly during a frame change I noticed a very quick blue screen with writing. At the time I never thought anything of it as it ...
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1answer
167 views

How to bring little changes in DES algorithm

I thought of implementing DES modes of operation as a project...But my guide asked to change or to modify the DES algorithm in such a way to overcome drawbacks of DES...So is there any way to do ...
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1answer
173 views

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 $p$ , $q$ ...