2
votes
0answers
27 views

Encryption with Deduplication [duplicate]

Suppose I have a file server running ZFS with file deduplication enabled, and I have two users that are sharing files: Alice and Carol. If Alice uploads huge_file.tgz to her www/ directory, and Carol ...
4
votes
1answer
147 views

Does Linear Cramer-Shoup have pseudo-random ciphertexts?

"Linear Cramer-Shoup" is defined on pages 4 and 5 of $\:$ eprint.iacr.org/2007/074.pdf . Are the ciphertexts in Linear Cramer-Shoup computationally indistinguishable from uniform under a ...
-1
votes
2answers
980 views

Where to store the private key and the public key in a communication protocol

I want to create a simple secured connection protocol over TCP/IP. I just want to connect from my mobile device to a server securely. Firstly I thought to use an SSL connection, but I changed my ...
2
votes
1answer
157 views

Selecting a large NUMS Safe prime

Suppose I want to use the following simple hash function. For a mesage $m$, take some public $a$ and prime $p$ and raise $a^m \bmod p$ (never mind the computational expense of this operation). This ...
3
votes
1answer
297 views

When confusion is applied during encryption?

I know confusion is used in cryptography to make it more difficult to identify any relationship between the ciphertext and the symmetric key. I want to know when the confusion is applied during ...
1
vote
0answers
287 views

computing inverses in truncated polynomial rings manually for NTRU encryption [duplicate]

Can someone explain how to find inverses in truncated polynomial rings manually (i.e. on pen and paper)? As an example from the tutorial: Example. Take $N=7$, $q=11$, $a=3+2X^2-3X^4+X^6$. The ...
7
votes
3answers
669 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 ...
1
vote
0answers
77 views

Can a LIRA system work with cjdns or other decentralized meshnets?

LIRA (Lightweight Incentivized Routing for Anonymity) is a scheme to incentivize participants in Tor to contribute resources, in particular bandwidth. The paper talks about it being used for Tor. Can ...
4
votes
1answer
886 views

BCrypt vs Key Stretching MD5

Ars technica posted an article about the latest in cyber warfare from the stuxnet crew. They key stretched MD5 by iterating it 10,000 times. It seems to be effective at handicapping HashCat's gpu ...
6
votes
2answers
711 views

Can I use a key-derivation-function as the hash function H in SRP?

In the Secure Remote Password Protocol, the verifier must be stored on the server. In the case of a server compromise, an attacker could obtain these verifiers. If nobody reused passwords, this ...
0
votes
1answer
247 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: ...
3
votes
1answer
355 views

Understanding a Blowfish cryptanalysis

I'm reading a cryptanalysis on Blowfish, and I've come across something that I don't quite get. Let's denote $$\delta = a \oplus a'$$ where a and a' are bytes that cause a collision in some S-box ...
-1
votes
2answers
457 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 ...
2
votes
1answer
323 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 ...
1
vote
0answers
65 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
votes
1answer
187 views

Is there an efficient way to hide the encrypted plaintext length with a block cipher?

In block cipher modes of operation for encryption on input of a plaintext of $N$ blocks (We assume that the input size is always a multiple of the blockcipher mode: $N·16$ bytes) the size of the ...
2
votes
2answers
233 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 ...
1
vote
1answer
439 views

Partial decryption of large file in AES-GCM (or other modes)?

Lets assume a 4gig file that is internally made of 1 million pages of 4k bytes each (page). the file was originally AES-GCM encrypted these pages (or entire file) lives across the internet i.e. ...
4
votes
2answers
1k 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 ...
1
vote
0answers
236 views

Method and explanation for calculating difference in speed between DES and RSA

Our assignment asks us to convert an RSA speed in bytes per second to a DES speed in bytes per second. Our professor's treatment of this ("RSA is 100 times slower than DES") seems insufficient. Could ...
2
votes
1answer
286 views

Is this method for exchanging private key using RSA sound?

Bob know's Alice's public key, and he wants to make sure he's connecting to the one which has that key. Furthermore, Alice wants to verify when she gets a connection from Bob who'll give his public ...
5
votes
4answers
1k views

Is SHA-256 secure as a CTR block cipher?

Generate a 256-bit random nonce. XOR it with a 256-bit reusable symmetric key. This is x. We represent numbers in simple binary instead of a counting function. ...
2
votes
1answer
94 views

How difficult is it to check if a group element is in a sub group?

I am just curious. We have a group $G$ and its subgroup $H$ with a generator element $h \in H$. How difficult is it to check for $x \in G$ that $x \in \langle h \rangle$? Is there a better way than ...
1
vote
1answer
329 views

What are some different cryptography methods?

Some of the most effective cryptography methods and algorithms are based of factoring large prime numbers (e.g. RSA). I'm curious whether there are some other cryptography methods. Somethings that is ...
6
votes
3answers
587 views

Finding roots in $\mathbb{Z}_p$

Is there an efficient way (algorihtm) to compute the solutions of the congruence $x^n\equiv a \pmod p$? $n\in \mathbb{N}$ $a\in\mathbb{Z}_p$ $p$ is a large prime number Note that: By efficient I ...
3
votes
1answer
601 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 ...
0
votes
0answers
67 views

Strength of Combining Hash functions [duplicate]

If I combine two hash functions, what will the impact on the strength of the resulting function. If I combine in following way: H1*H2 (multiply) H1 + H2 (concat) H1 Xor H2 H1 (H2) EDIT: Lets say H1 ...
5
votes
1answer
750 views

Should the secret key of Shamir's secret-sharing algorithm be interpreted byte by byte?

Should the secret message of Shamir's secret-sharing algorithm be interpreted and processed byte by byte? Interpreting it byte by byte makes it easier to process, but in case one of the shareholders ...
2
votes
1answer
58 views

Equivalents to a physical hat+shaking?

I would like a multiparty protocol, secure in the honest-but-curious model at least, but hopefully other situations as well, that can do the following: every party among $\{P_1, P_2, \ldots P_n\}$ ...
4
votes
2answers
330 views

Modulus for elliptic curve point multiplication

I want to implement a point multiplication ($k \cdot P$) operation on FPGA. I have a BN curve $y^2=x^3+2$, and a scalar value $k$. The $x$ and $y$ coordinates of point $P$ are of 256 bits. In the ...
1
vote
1answer
165 views

Exponentiation In PBC library

I need to compute a function $h^l$, where h is an element of G2 and l is a rational number. How can this be done using the PBC library? I have converted the h to ...
2
votes
0answers
249 views

One-time pad and perfect secrecy properties

I have a homework problem: Explain how to find $m_{0}$ and $c$ such that $P[c=c': k \leftarrow K, c' \leftarrow E(k, m_{0})] > 0$ where P is probability and k is chosen uniformly. I do not know ...
1
vote
0answers
218 views

Use curve25519 for ElGamal crypto

DJB described curve25519 in his paper which can be found here: http://cr.yp.to/ecdh/curve25519-20060209.pdf. It seems that the main purpose was for Diffie-Hellman key exchange. I think this means that ...
2
votes
1answer
283 views

How are Elliptic Curve Cryptography and Pairing Based Cryptography related?

I have been doing a project that uses the PBC library developed by Ben Lynn. But I am still not clear on how PBC is related to ECC. I know that this is a site for complex crypto QA, but I did not know ...
1
vote
1answer
489 views

Possibility of factorisation of rsa modulus due to vulnerability in java implementation code

Below is my implementation of the RSA algorithm. Actually I'm choosing the private key (d) instead of public key (e) and computing the public key.It is working fine but I want to know if this is a ...
1
vote
2answers
2k views

is AES secure for java application licensing

I have to license a java application and want to code a quick implementation, the scheme I came up with is: 1) The Application calculates a string X which we assume to be the md5 sum of the ...
0
votes
1answer
2k views

GPG vs PGP vs OpenSSH and management of them [closed]

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 ...
1
vote
1answer
125 views

Security relevance of random factor in Paillier

In the Paillier cryptosystem [1] the encryption of $m \in \mathbb{Z}_N$ with randomness $r \in \mathbb{Z}_n^*$ is $c = g^m r^n \bmod{n^2}$. The additive-homomorphic property of the system shows that ...
6
votes
2answers
6k views

What is the difference between MAC and HMAC?

In reference to this question, what are the "stronger security properties" that HMAC provides over MAC. I got that MAC requires an IV whereas HMAC doesn't. I also understood that MAC may reveal ...
0
votes
2answers
187 views

Is solving a modular linear equation a hard problem when the coefficient is not an invertible element?

Assume that we have a linear equation like this: $$ax=b \pmod n$$ when $x$ is the unknown, and $a$ is not an invertible element in $n$. is finding $x$ a hard problem? (by solving I mean finding an ...
1
vote
3answers
708 views

What goals is homomorphic encryption aiming to solve?

As I understand from this article about homomorphic encryption, it mainly aims to enhance the security of cloud computing. We should be able to encrypt data and send it to the cloud. After it is send, ...
0
votes
1answer
282 views

How to secure a mental poker protocol? [closed]

I would like to implement a mental poker protocol in a secure fashion. How should I go about that without (preferably) infringing on the Mental Poker Framework patent?
3
votes
2answers
592 views

Simple RC4 key generation scheme

I would like to ask you about your opinion on the following scheme of combining a master key and a nonce and stretching the result to the full 256-bytes RC4 key. Master key $K_m$ is a pre-shared ...
3
votes
3answers
345 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 ...
3
votes
2answers
373 views

While generating a random Elliptic curve what are the conditions i have to considerd?

I want to generate a random elliptic curve over a prime field. What are the conditions I should satisfy? For the NIST recommended standard ECC-224 bit curve with prime $p=2^{224}-2^{96}+1$, a ...
1
vote
1answer
167 views

How to solve the reverse of an equation that uses MOD?

I've been tasked with reverse engineering an unknown crypto function. The function uses the following constants: $a=380951$: I noticed that this is a prime number $b=3182$: I noted that this is a ...
5
votes
1answer
137 views

In RSA, how to make sure that $p-1$ and $q-1$ are still hard to factorize?

See this question. The comment by Brett Hale stated: On the other hand, ensuring $(p - 1)$ has a large prime factor requires very little extra effort. What's actually the 'little extra effort'?
1
vote
2answers
224 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 ...
0
votes
1answer
70 views

Is it possible to create a Bilinear Function with Already Assigned “Multiplicative” Input Groups?

Assume that we have an already assigned Multiplicative Cyclic Group $\mathbb Z_p^*$ with order $q=p-1$, and $p$ is a prime number, is it possible to create a bilinear function $\hat{e}: \mathbb Z_p^* ...
4
votes
0answers
138 views

Unique GCM/CCM initial counters without recipient side message counters

I am implementing the encryption layer for a communication protocol. The bulk encryption method used is either AES-CCM or AES-GCM. Due to implementation details, encryption of packets is usually, but ...

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