# All Questions

518 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 ...
64 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 ...
641 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 ...
57 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 $\{P_1, P_2, \ldots P_n\}$ ...
310 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 ...
136 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 ...
225 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 ...
204 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 ...
235 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 ...
417 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 ...
1k 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 ...
1k 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 ...
116 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 ...
4k 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 ...
177 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 ...
625 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, ...
244 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?
486 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 ...
322 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 ...
277 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 ...
152 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 ...
135 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'?
180 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 ...
63 views

838 views

### Fastest multiplication algorithm for efficient exponentiation in C++?

First I apologize if this question is better tailored for SO, but since I'm using the method for crypto stuff, I thought I'd ask anybody that might know here. Karatsuba algorithm does a pretty good ...
315 views

### Digital signatures in SSL/TLS-like protocols

The TLS protocol includes an optional Server Key Exchange message that is signed by the server. It seems to me that this message is digitally signed only to prove to the client that the message ...