# All Questions

212 views

### How can I store a combination of multiple pass phrases?

Let's assume we have 2 phrases, one is the real password from a user, and the other is generated from the real password and almost impossible to guess. You would need both to authenticate a user. What ...
176 views

### Is there a way to provide proof of batch RSA security?

Suppose we have two encrypted messages with two different public key issued from the one server. There is a client who wants to send these to messages to the server. In the middle there is an ...
981 views

### Hash or encryption function for challenge-response protocol?

Say I have an authentication protocol where the shared secret is never transmitted. The server passes a challenge to the client and the client calculates a response using an algorithm where the ...
111 views

### Is it possible to spoof an identity cert modulus?

I was looking at FOAF+SSL and wondering if its possible to spoof the modulus of the browser certificate so that the FOAF and browser certificate's modulus match?
1k views

### Where can I find Secp256k1 ECDSA test vectors?

I`m currently implementing an ECDSA library based on curves like secp256k1. I would like to test it using some test vectors, like http://csrc.nist.gov/groups/STM/cavp/documents/dss/ecdsatestvectors....
24 views

### Client side encryption / hashing of “person ID's” with password?

What we're looking for A solution where data is stored and retrieved (!) from a server using a person ID that can only be known at the client (form of ...
39 views

### Finding $f^{-1}$ in the YASHE keygen algorithm

In the YASHE (Yet Another Somewhat Homomorphic Encryption) algorithm, the beggining of the key generation step specifies: Sample $\ f',g ← χ_{key}$ and let $\ f = [tf' + 1]_q$. If $\ f$ is ...
99 views

### Calculating Polynomial Inverse with extended euclid in java

I'm trying to understand the NTRU-PKCS and therefor I wanted to code a naive Version of it. Now my Problem: I tried to calculate the inverse of a Polynomial with an extended Version of euclids ...
32 views

### First preimage resistance check

So I have $H: \{0,1\}^* \rightarrow\{0,1\}^n$ a hash function resistant to the second preimage and to collisions. Let there be a function $H' : \{0,1\}^* \rightarrow \{0,1\}^{n+1}$ with the following ...
70 views

### Application level encryption and key renewal

I had posted this question on stackoverflow and been asked to move it to crypto. What is your view on this? What is the doability? I have a question related to encrypting data in the database, at the ...
55 views

### What's the difference between PBKDF and SHA and why use them together?

I've been reading a little bit about hashing lately and according to AgileBits, they use "SHA512 within PBKDF2" in their new vault file. I've looked in Wikipedia for both names and I know PBKDF2 is a ...
86 views

### Fixed primes in discrete logarithm

The discrete logarithm problem is to find $z$ when the inputs are $g,h,p$ where $g^z\bmod p$. Supposing if you fix $p$ then does the problem become any easier to attacks and is there a $(\log p)^c$ ...
99 views

### RSA Encryption problem for Discrete Math

I am doing practice problems for my upcoming final exam, and am having trouble with this RSA encryption problem. If any one could check to see if i did these correctly, it would be greatly appreciated....
57 views

### Does revealing shares of the result reveals shares of the inputs?

Suppose Alive and Bob have shares of two polynomials $P,Q$, say, Alice knows $P_A,Q_A$, Bob knows $P_B,Q_B$ s.t. $P=P_A+P_B$ and $Q=Q_A+Q_B$. They perform some operation $f$ over the shared values, to ...
122 views

### How much weaker is AES-64 than AES-128?

It's hard to say exact QC specs, but let's assume we have decent a quantum computer using Grover's algorithm that is able to half AES-128 keyspace to that of AES-64. How long will a bruteforce attack ...
53 views

### Why are the bit lengths of keys and digests equal in Lamport signatures?

In Lamport's one time signature scheme: One way function to convert a pseudo random number private key to a public key takes $\{0,1\}^n$ and returns $\{0,1\}^n$. Cryptographic hash function to ...
91 views

### How to detect what crypto-method is used by Filecoder.Q?

I have 2 different images, one original, and one locked by a malware detected by eset as "Win32/Filecoder.Q". How to detect the encryption method that is used and the key, that is not using any ...
56 views

### Key management and derivation - Allow changing of the passphrase

I'm working on a program, which allows encrypting files before storing it on a cloud service. Currently I'm trying to figure out how to derive and store the keys. First, I wanted to use a simple ...
32 views

### Can multi-prime RSA be used to create an abuse-resistant lawful interception mechanism?

New to site so this may have been asked before: Can multi-prime RSA, i.e. where N is product of three or more distinct primes, be used for secure communication while allowing distinct authoritative ...
28 views

### Steps to encrypt endorsements to a petition

I plan to circulate a petition, asking people to support it. This petition will reach a senior government official. In regular circumstances, people would support such petitions by writing their ...
57 views

### What would be a typical value for the security parameter of the Fully Homomorphic Encryption over the Integers scheme?

The parameters of the Fully Homomorphic Encryption scheme by Dijk et.al are chosen according to the value of the security parameter ${\lambda}$, section 3 of the aforementioned article. What is the ...
61 views

### How SAM modules secure transactions?

As you know SAM Modules are used mainly in the electronic payment industry. Due to the low security of key storing in general storage devices or MCUs, Manufacturers used SAM modules for secure storing ...