# All Questions

129 views

### Why can't NORX produce intermediate auth tags like Keyak can?

Why can't NORX produce intermediate auth tags like Keyak can? Keyak appears quite attractive because of this, but seems to be slow in the absence of hardware acceleration.
58 views

### Practicality of codebook in current-day secret communications

Codebook appears, if I don't err, to be an antiquitated topic rarely touched upon in discussions of modern cryptography. Couldn't codebook nonetheless be of high practical utility and even be ...
152 views

### Help understanding basic Franklin-Reiter related message attack

I am trying to understand this attack at the most basic level. I set up the following basic scenario: Let the public encryption exponent, e = 3. Let p, be some arbitrary but known (to the ...
303 views

### Autocorrelation in Autokey

I know that Vigenère can broken using auto-correlation (as explained at cryptool-online.org). Now my question is: Why does this also work with autokey (tested it using crypttool)? To prove that I ...
95 views

### Parallel variant of Carter-Wegman MAC with incremental property

Is there any variant of the Carter-Wegman MAC algorithm that is fast, parallel and has the property of incremental crypto?
328 views

### Regular MACs vs Carter-Wegman MAC

Carter-Wegman MAC variants (VMAC, UMAC etc) are known to be very fast and efficient when compared to MAC algorithms that are based on block ciphers and compression functions (like HMAC, CMAC etc). ...
619 views

### Does omitting the first two lines of RC4's pseudo-random generation algorithm weaken the cipher?

A particular educational software program published by a U.S. government agency uses a variant of RC4 to obfuscate its data files (see Stack Overflow question). The variant of RC4 in question is ...
184 views

### Is it secure to send the hash along the message without encryption?

Lets suppose Alice send to Bob a message $M$ along with its hash value say $H$ which is calculated using SHA3 algorithm. It is sent on the network where it got read by Eve and she does not make any ...
109 views

### Is BBS used for generation of keys for any modern cryptosystem?

Is there any (current) cryptosystem or digital signature or cryptographic primitive that uses the BBS PRG in order to generate its secret keys?
50 views

### Can a Cramer-Shoup public key have two different private keys?

Since I am new to the Cramer-Shoup algorithm, I would like to know: Is it possible to have two different private keys for a public key due the key pair generation algorithm that Cramer-Shoup uses? I ...
112 views

### Differential Cryptanalysis for Hash functions

How is differential cryptanalysis used to attack hash functions? I've been struggling through a couple academic papers and thesis's on the subject but they all sound like greek to me. Does anyone know ...
662 views

### A mathematical explanation of the DES encryption system

I need a mathematical explanation of what does the DES encryption system really do. This means I need more explanation than the one that offers FIPS, which is more an explanation for computer ...
91 views

### Why do the subexponential algoriths for the DLP not work for the ECDLP?

Elliptic curve cryptography is much more secure for the same parameters because attacks that work on the DLP do not work on the ECDLP. Why do the attacks fail in the latter case?
84 views

### Step by step conceptual implementation of AUTHENTICATED Diffie-Hellman?

I'm already doing classic DH with pre-shared key in my setup, and it prevents people knowing the same password from eavesdropping on others' traffic. But it doesn't cover situations where a third ...
41 views

### What information about the ciphertext can an attacker discern if a key is used too many times?

Suppose that I use Blowfish or XTEA (both secure block ciphers with 64-bit block size) in CTR mode. In these cases, I need to change the key after $2^{16}$ blocks to avoid leaking information with ...
71 views

### k(k-1)/2: Combinations and the Birthday bound

Disclaimer: I'm new to cryptography. Background: I'm reading Cryptography Engineering by Ferguson, Schneier, and Kohno, where, in Chapter 2, the authors write this: Question: What is $k(k-1)/2$ ...
31 views

### How do we calculate DHKey using A's public key and B's private key?

I have 2 set of public/private keys. I would like to know how I can calculate DHKey. e.g: ...
80 views

### Is it okay for a non-cryptographer to submit crypto code to an open source probject? [closed]

I am not a cryptographer, nor do I claim to be. However, at times I have wanted to contribute to open source cryptography projects such as libsodium. The maintainer of libsodium is a cryptographer, ...
49 views

### Universal reencryption for signatures

Universal reencryption is an interesting encryption primitive. Attempts to build signatures schemes or protocols with authentication incorporating it have frequently failed though. A plausible ...
36 views

### Are there any historic examples of breaking the one-time pad because of a careless key re-use? i.e simple attack on a multiple-time pad?

It doesn't have be using a truly random key, (it could be the Enigma) but the attack must be based on XORing two parts of ciphertext.
77 views

### Advantages of HS1-SIV over ChaCha20-Poly1305-SIV?

What advantages does HS1-SIV have over ChaCha20-Poly1305-SIV? I know that both use the ChaCha stream cipher, but I am trying to understand why HS1-Hash is a better MAC. Edit: To hide the Poly1305 ...
62 views

### Effective key length of Two-Key Triple-DES

What's the effective key length of Two-Key Triple-DES, for some (possibly several) reasonably well-defined and sensible definitions of effective key length, say assuming attack using ample chosen ...
170 views

### Implementing hmac+bcrypt in bash script

I was recently reading Mozilla's Secure Coding guidelines and found their password storage method interesting. They combine an hmac hash of the password with bcrypt which allows for added security ...
33 views

### Are timing attacks exploitable if each key is used only once?

Suppose that one performs (for example) AES-GCM encryption and decryption using an algorithm that is vulnerable to timing attacks, but each key is used only once. Is it still possible to perform a ...
212 views

### Is there a formal definition of what a distinguisher is?

I've often been reading about (polynomially bounded) distinguishers in books or papers. Although by name and intuition it is somewhat clear what a distinguisher is and does, but i am asking myself ...
96 views

### Understanding the distinguisher for a PRG

Given the following definition of a psuedorandom generator, I'm having trouble understanding what exactly the "distinguisher" D is outputting, and when?