# All Questions

88 views

### How to hash a set of elements

Imagine the following senario. We have $n$ participants. Participant $i$ has a set of elements $S_i$ with the elements being in a random order, possibly different for each participant. The ...
72 views

### Is it possible to securely combine multiple hashes without hashing them?

Let's say we have 1000 files and 1000 already computed cryptographic hashes for those files. Now we want to derive a single hash that authenticates all of them. Is there a more efficient way to do ...
129 views

### Quantum vs. regular computing time to break ECC?

How long exactly would it take for a regular computer to crack an elliptic curve public/private key via bruteforce, vs. a quantum computer using Shor's algorithm with a couple thousand qubits? Can ...
62 views

146 views

### DES: How to find the Inverse of the Initial Permutation?

I am doing a DES problem by hand and I want to know how you calculate the inverse of the initial permutation. I know what the permutation is, but how do you find it based off the given initial ...
144 views

### How to determine if padding has been used while encrypting a message with RSA?

I am trying to decrypt a RSA encrypted text file. I have a 2048 bit public key. Analyzing the public key with openssl reveals the exponent used is 3. ...
132 views

### Public key exponent coprime with totient proof

I read this question a while back (In RSA, why is it important choosing e so that it is coprime to φ(n)?). I was wondering whether there is a proof that shows that a public key exponent e that is ...
207 views

### Is it bad design to reuse an AES key?

The company I work for needs to develop a simple system where, for each client, we encrypt a token on our server, which is then transmitted to the client. The decryption is performed by the server ...
128 views

### Given $g,g^t$ in a cyclic group of order $pq$, is it hard to compute $g^{t^{-1}}$?

Suppose we have a group $G$ cyclic of order $pq$ , where $p,q$ are primes. Let $g$ be a generator of $G$ and $t\in \mathbb{Z}_{pq}$. Having $g$ and $g^t$, it seems to be very hard to find $g^{t^{-1}}$,...
69 views

### What is the difference between LCG and Affine cipher?

What is the difference between LCG and Affine cipher? More specific: What are they used for, and what are the structural differences between them?
69 views

### Cryptographic hash with ability to ignore specific bits based on a hidden pattern?

I'm looking to use password-style hashing to validate an environment, where some parts may be irrelevant. For example: ...
73 views

### How does padding oracle attack work with bytes larger than possible length?

I am trying to understand how the POODLE attack would actually be implemented. In the original security advisory from Möller, Duong and Kotowicz [POODLE 14] the following example is presented: ...
64 views

### Is it OK to use a secret IV as key when creating keyed MD5 checksum for fixed-size data?

Is it OK to use a secret IV as key when creating keyed MD5 checksum for fixed-size data? Because data size is known, attacker cannot append anything. And I think it's hard to raise chosen-plaintext ...
78 views

### Improving security of (authentication) protocol

I have a basic protocol which tries to authenticate messages going from client to server. Basically it is like this: Imagine I want to send message M to server. Client computes a MAC over the message....
67 views

### How is a group element converted into a key?

I've only just started research on cryptography so I apologize if this is a basic question or I'm getting terms confused. I'm researching braid group cryptography and currently looking at the Anshel-...
128 views

### A “one time pad” can be thought of a Vigenere cipher with

A "One Time Pad" can be thought of a Vigenere cipher with... An infinitely long key A secure symmetric key Multiple ciphertext alphabets A columnar transposition I had this question come up ...
26 views

### What communications security protocols exist that aren't based on PKC?

Lets say that you have two devices that need to communicate in a secure manner. These devices can share secrets before communication takes place (This sharing of secrets occurs over another secure ...
60 views

### How does the size of the prime affect Elliptic Curve Bit Security?

I am using the MIRACL Library to implement an Elliptic Curve Diffie Hellman based Key Exchange according to ECDH-Scheme-Wikipedia. Referring to the Miracl Docs they suggest a few curves. Each curve ...