53 votes
Accepted

How are side-channel attacks executed? What does an attacker need to execute a side channel attack?

Here's a very simple timing side channel attack that you might even see in movies. Suppose you're trying to log in to a computer with a password, and the victim compares your password byte by byte ...
Squeamish Ossifrage's user avatar
34 votes
Accepted

How can I force slow decryption in the browser?

As I indicated in the comments, I believe a non-cryptographic solution may be the best for this task, where instead of attempting to measure "10 minutes" by the average amount of time it ...
Mark's user avatar
  • 12.5k
25 votes

How can I force slow decryption in the browser?

I don't know about enforcing browser decryption, but here's an old trick for fast encryption and slow decryption if you understand RSA. Generate a 2048-bit RSA modulus $N=pq$ and a random exponent $d$....
Daniel S's user avatar
  • 22.9k
21 votes
Accepted

How long does it take to crack RSA 1024 with a PC?

RSA-768 took 2000 years of 2.2Ghz single-core Opteron from the year 2009. DJB et al wrote in 2013 (see page 30) (see also: 29C3: FactHacks (EN); slide 87/112; about 10 minutes) that RSA-1024 would ...
Z.T.'s user avatar
  • 824
20 votes

How are side-channel attacks executed? What does an attacker need to execute a side channel attack?

This is an attempt to an Explain to me like I'm five style answer: Assume you have a bank vault with a mechanical combination lock. Your cipher in this case is "combination lock". At first sight it ...
Stefan D.'s user avatar
  • 301
16 votes

Cryptography elements needed for a story

Though quantum computers fit the requirements, I'm not sure they are the best option. A general purpose quantum computer capable of attacking modern encryption (RSA, AES) would have serious ...
Meir Maor's user avatar
  • 11.8k
16 votes

Can I change the radio frequency according to my encryption algorithm?

More physical layer security than encryption. Spread spectrum wideband radio using frequency hopping does this. https://en.m.wikipedia.org/wiki/Frequency-hopping_spread_spectrum What is required is a ...
kodlu's user avatar
  • 22.1k
11 votes
Accepted

Encryption and decryption with Diffie-Hellman

The purpose of Diffie-Hellman is solely to establish a shared key, $K$. Taken from Wikipedia: Traditionally, secure encrypted communication between two parties required that they first exchange ...
thesquaregroot's user avatar
11 votes

Are there any cryptographic algorithms, which lets the user apply some modifications on the encoded data, without decoding it?

Can I modify encrypted data without accessing it? if there is an example appreciate it If access means altering the data without decryption as an attacker then the answer is yes for messages without ...
kelalaka's user avatar
  • 48.3k
10 votes

What are the smallest possible RSA private and public keys?

Per the definition of RSA in PKCS#1v2.2 In a valid RSA private key, the RSA modulus $n$ is the product of $u$ distinct odd primes $r_i$, $i=1$, $2$, …, $u$, where $u\ge2$. That makes $n=3\cdot5=15$ ...
fgrieu's user avatar
  • 140k
10 votes

Are there any cryptographic algorithms, which lets the user apply some modifications on the encoded data, without decoding it?

If (and ONLY if) it was encrypted with a special "homomorphic" encryption scheme, then you can do the operations allowed by that scheme. Those are almost never used in practice currently (...
SAI Peregrinus's user avatar
8 votes
Accepted

Would creating a custom human language be stronger protection than encrypting a known human language?

$$\texttt{NO}$$ In short; $$\text{We are living in a world where that is ruled by Kerckhoffs's principles}$$ The above may not be totally clear as indicated by Maarten in the comments. The We is ...
kelalaka's user avatar
  • 48.3k
8 votes

Why does the Bombe not consider the Ringstellung when determining stecker pairs?

I didn't want to delete this question, but it seems like after pondering this for a week I finally understand right when I seek help online. When the ring setting and the rotor position all increase ...
Queso Pez's user avatar
  • 301
8 votes
Accepted

Advantages and possible usages of encryption schemes with probabilistic decryption

Since when decrypting we always want to get the correct message back, there's no reason why we would want to make this ambiguous. It would have no security advantage (if the adversary can guess with ...
Yehuda Lindell's user avatar
8 votes
Accepted

Does file size significantly affect brute-force time?

AES is a block cipher and typically operates on large plaintext data by dividing it into blocks of fixed size (128-bits in the case of AES) and processing these blocks individually. Similarly ...
Daniel S's user avatar
  • 22.9k
7 votes

Is this toy RSA demonstration flawed?

You wouldn't be a Dave for presenting RSA, but you would be a Dave for following this description to implement anything, and you risk creating Daves with this presentation. I'm not saying you shouldn'...
Gilles 'SO- stop being evil''s user avatar
7 votes

RSA: The algorithm aside, how are we turning a string into an int and vice versa?

Basically there are two steps to this: encode the text to bytes - this generally requires a character encoding such as UTF-8 or Latin encoding; encode the bytes to integer - this is part of the ...
Maarten Bodewes's user avatar
  • 92.4k
6 votes

Is an invulnerable code possible (including brute force attack)?

No, If we assume that the mythical computer can brute force the multiple AES encryptions and there are many ciphertexts available which are encrypted under the same key and their corresponding ...
kelalaka's user avatar
  • 48.3k
6 votes
Accepted

NaCl allows decryption with the same public key as for encryption

Alice and Bob's keys are used to compute a shared key. Both parties compute the same key, which is used both encryption and decryption. This is a traditional, hybrid encryption system. Using only ...
Frank Denis's user avatar
  • 2,944
6 votes
Accepted

Is direct RSA encryption of AES keys secure?

This scheme suffers from a classic problem of textbook RSA which is mitigated e.g. by RSA-KEM (as outlined by kelalaka) or RSA-OAEP. When you compute $k^3\bmod N$, you'll experience that $$c=k^3\...
SEJPM's user avatar
  • 45.9k
6 votes
Accepted

Asymmetric Cryptography decryption

There is no known classical algorithm that can factor a 2048-bit modulus in feasible time. Shor's algorithm could do it in feasible time but this algorithm needs to be run on a large-scale quantum ...
AleksanderCH's user avatar
  • 6,425
6 votes

Good layperson analogy for password and encryption keys

A cryptographic key is a string of bits. For example, AES-128 uses 128 bits, each one of them being either 0 or 1. To be able to encrypt or decrypt, each one of those 128 bits must be set correctly. ...
jurez's user avatar
  • 161
6 votes
Accepted

Good layperson analogy for password and encryption keys

Regarding your understanding You mostly have things right, but not completely. a password is a (preferably) mnemonic string that is fed into a function that generates a much longer and complex string ...
Gilles 'SO- stop being evil''s user avatar
6 votes

Cryptography elements needed for a story

Party B will eventually succeed; still, to keep a modicum of suspense up, it must still be possible for them to fail An approach that will allow party B to succeed nonetheless To me the obvious ...
Richie Frame's user avatar
  • 13.1k
6 votes

Will Fernet’s key function at any timeframe?

No, there is generally no time factor when it comes to decryption. However, you should remember that even a single changed bit can cause decryption to fail. This is especially the case if that bit is ...
6 votes
Accepted

Factoring RSA if prime p is used as the private exponent

From Fermat's little theorem we know $$ a^p \equiv a \pmod{p}\,. $$ Applying this to the present problem, $c^p \equiv c \equiv x \pmod{p}$, and thus with high probability $p = \gcd(x - c, n)$.
Samuel Neves's user avatar
  • 12.4k
5 votes
Accepted

What is the exact meaning of the public key cryptosystem properties in New Directions In Cryptography by Diffie and Hellman

Well, it's good that you're trying to learn. However, learning from the original seminal papers does have some issues that you need to be aware of. For one, sometimes the original authors did not ...
poncho's user avatar
  • 146k
5 votes

Cryptography elements needed for a story

It's nice to see SciFi authors consulting professionals for technical viability problems. I've got something on my mind for you to consider. This is what I need: An algorithm such that, if you ...
DannyNiu's user avatar
  • 9,080
5 votes

Can you decode aes by hand if you have the key?

It would take you a while, but yes. You'd have to print out several tables that calculate things for you like $GF(256)$ field multiplication and inversion, but you could do it. It would be slow and ...
Myria's user avatar
  • 2,575
5 votes

AES Key vs RSA Key

AES is a symmetric key algorithm, which means there is just one key, used both to encrypt and decrypt. This is different from RSA, where you have two keys - a private one and a public one, related in ...
meshcollider's user avatar
  • 1,573

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