1
vote
2answers
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.
2
votes
1answer
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 ...
2
votes
1answer
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 ...
2
votes
2answers
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 ...
2
votes
1answer
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?
6
votes
1answer
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). ...
6
votes
1answer
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 ...
-3
votes
1answer
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 ...
0
votes
2answers
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?
0
votes
1answer
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 ...
3
votes
1answer
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 ...
3
votes
4answers
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 ...
3
votes
1answer
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?
1
vote
2answers
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 ...
1
vote
1answer
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 ...
0
votes
2answers
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 $k(k-1)/2$ ...
-3
votes
1answer
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: ...
1
vote
1answer
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, ...
1
vote
1answer
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 ...
0
votes
0answers
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.
2
votes
1answer
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 ...
2
votes
1answer
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 ...
0
votes
0answers
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 ...
2
votes
1answer
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 ...
6
votes
2answers
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 ...
0
votes
2answers
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?
3
votes
0answers
38 views

DES_cblock and Key Recovery

I'm trying to get my hands on the key that OpenSSL uses for a DES encryption. The key is based off a random number generator with a seed taken as parameter. The code used is below, provided as part ...
1
vote
0answers
122 views

Fiat Shamir with S^3

I'm trying to do Fiat Shamir but with $I = S^3 \pmod n$ where $S$ is the secret key. How will I prove that I know the cube root? I tried doing the old formula but with instead with $(RS)^3 = x*I \pmod ...
0
votes
1answer
39 views

How would the opponent defraud this secure communication?

I am new in the cryptography and the information security problems, I try to understand things as much as I can and I know it's really complicated in the beginning. Considering the communication ...
7
votes
1answer
61 views

Difficulty to find any preimages $a$ and $b$ for given $V$ so that $H(a) \oplus H(b) = V$?

Suppose I have the values $a$, $b$, and $V = H(a) \oplus H(b)$ with inputs $a \neq b$ and $H$ being SHA-224. None of these values are a secret. How secure is it to assume that no other possible values ...
1
vote
0answers
21 views

C implementation of GEA/3 [closed]

Can somebody please point me to an implementation of GEA/3 (an encryption algorithm) in a high-level language (preferably C/C++)? I looked for a while but could only find block diagrams and ...
1
vote
1answer
76 views

Shouldn't a signature using ECDSA be exactly 96 bytes, not 102 or 103?

Attempting to use openssl to create a signature is confusing on several levels: If I'm using it to sign a hash that I've already created (HMAC-SHA-384-192, specifically), a. why must I specify ...
4
votes
1answer
86 views

ChaCha20 immune to timing attacks

What are the reasons because of which ChaCha20 is immune to timing attacks ? Also why is not AES immune to timing attacks?
1
vote
2answers
53 views

Gaussian function in lattices

Probability density function of gaussian distribution is $$ 1/{\sqrt{2 \pi} \sigma} \times {e^{{(x-c)^2/ 2{\sigma}^2 }}} $$ in lattices we assume $$ \sigma =s/\sqrt{2 \pi} $$so the gaussian ...
1
vote
0answers
29 views

Does extra encryption improve the security of CBC and CTR?

I am learning about cryptography and during my research and reading I had a question. When looking at information leakage and CBC mode, I asked if there is a way to improve this with by using the ...
1
vote
1answer
40 views

What do associated data and message numbers mean?

I'm reading an article about authenticated encryption and don't understand some inputs to an encryption function. They are associated data, public and secret message numbers. Can you explain me their ...
6
votes
2answers
743 views

Public key crypto without modular arithmetic?

This comment from Reddit math, in response to a statement about how people can communicate secrets to each other with a third party listening, has a very small, simple example of public key ...
4
votes
1answer
542 views

Curve25519 vs “Million Dollar Curve”

Quoting from the Million Dollar Curve website: By using publicly verifiable randomness produced in February 2016 by many national lotteries from all around the world, we propose to generate a ...
0
votes
1answer
85 views

How to decrypt RSA if ciphertext is less than the modulus and e=3?

I'm given a public key. Using openssl rsa ..... I got the public key has the exponent as 3. When I calculated the size of the ciphertext, it is 8 bits smaller than the 2048-bit modulus. How can I ...
0
votes
0answers
16 views

How does the speed of fast stream ciphers compare to non-cryptographic PRNGs?

Modern stream ciphers are so fast that I am wondering if they are good choices for non-cryptographic applications. Specifically, I am wondering how much slower optimized ChaCha8 or hardware-...
1
vote
2answers
133 views

Determine if a public key point y is negative or positive, odd or even?

Take an elliptic curve cryptography public key (x, y) and its additive inverse (x, -y). How do you identify which is the positive point and which is the negative point? Examples: Private key 1 -> (x,...
1
vote
3answers
126 views

Is all of encryption based on xor?

For a long time I've been under the impression that all of encryption uses xor at its basic level. Is this true? What other method could be used to encrypt plaintext with a key? Asymmetrically, as ...
0
votes
0answers
24 views

Is RSA safe anymore? [duplicate]

Some people may have heard of Shor's algorithm. It allows for integer factorization on a quantum computer. This wasn't a problem a little while ago since we didn't have any quantum computers. Google ...
3
votes
1answer
103 views

Do 2DES and 3DES2 have the same effective key length?

I am following the notes "Introduction to Modern Cryptography" by Bellare and Rogaway, and on the chapter about blockciphers there is the following claim (page 11 of https://cseweb.ucsd.edu/~mihir/...
0
votes
1answer
67 views

Are any public key algos commutative?

Are there any public key encryption algorithms that allows for arbitrary ordering of crypto operations (commutative). That is, given a plaintext "message1", the following operations work to doubly ...
3
votes
0answers
44 views

How to make a “zero knowledge” cache/key-value store

I'd like to use a possibly insecure cache for storing expensive-to-calculate sensitive information. My requirements are: If the cache ever gets compromised it should reveal nothing about its ids or ...
1
vote
1answer
70 views

Is there an additive homomorphic encryption that supports exponentation

For example say we have two numbers a and b. Now is there any partial homomorphic encryption scheme that allows to compute (a-b)^2 over the ciphertexts of a and b without round trips.
0
votes
1answer
186 views

What happens when cbc+hmac get a replay attack?

If it use AES-CBC and HMAC-SHA256 for message send online, and someone try to replay attack on this message. Can the attack be successful? what will be happen when attacking?
0
votes
4answers
661 views

Do Brute-Force Attacks and Cryptanalysis refute Kerckhoffs's principle? [closed]

According to Kerckhoffs's principle "A cryptosystem should be secure even if everything about the system, except the key, is public knowledge." Now I want to throw in a provoking formula of mine which ...
2
votes
2answers
67 views

Obtaining Diffie-Hellman generator

In the Wikipedia article on Diffie-Hellman, the algorithm calls for a large prime modulus, $p$, and a generator, $g$, which is a primitive root of $p$. As far as my knowledge of number theory goes, ...

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