# Tag Info

Accepted

That number was so quick to factor because its factors are extremely close together, i.e., it factors as $\left(\lfloor\sqrt{n}\rfloor + 70\right)\left(\lfloor\sqrt{n}\rfloor - 68\right)$. Some ...
• 11.6k
Accepted

### How can C rand() be exploited if a secure seed is used?

The ISO/IEC 9899:1990 edition of the C standard contains: EXAMPLE     The following functions define a portable implementation of rand and ...
• 122k
Accepted

### Did a certain cryptography method get abandoned due to security flaws in the past?

You could be thinking about the Merkle-Hellman knapsack cryptosystem. It was invented in 1978 and everything seemed well and good until it was completely broken six years later in 1984 by Shamir - it ...
• 7,298
Accepted

### How is encryption broken today?

Modern encryption can be broken in practice even when the algorithms are theoretically secure. There are a variety of ways this can happen: Side channel analysis could have played a part. The ...
• 19.2k
Accepted

### Why "1" in 51% attack on Blockchain network

From Bitcoin Wiki; A majority attack (usually labeled 51% attack or >50% attack) is an attack on the network. It is also called consensus attacks. It is only to demonstrate that one needs the ...
• 43k
Accepted

### What does a "real" quantum computer need for cryptanalysis and/or cryptographic attack purposes?

For example: the 5-qubit quantum computer created at MIT by using the technique of ion traps succeeded in prime-factorizing 15. Does that mean that since it succesfully managed that, that it is a all-...
• 336

### Did a certain cryptography method get abandoned due to security flaws in the past?

This is a shot in the dark, but could you be thinking of the Needham-Schroeder protocol? It was published in 1978 [1], and an attack was published as much as 18 years later, in 1996 [2]. It is not an ...

### Did a certain cryptography method get abandoned due to security flaws in the past?

DES has not been mentioned in the previous two answers. Although it was known to be quite weak from very early on it was widely used for a couple of decades at least, until newer algorithms (3DES, AES,...
• 31.2k
Accepted

### Is there any famous protocol that were proven secure but whose proof was wrong and lead to real world attacks?

One example is OCB2; Efficient Instantiations of Tweakable Blockciphers and Refinements to Modes OCB and PMAC by Rogaway. It is standardized in ISO/IEC 19772:2009. The author also provided a proof by ...
• 43k
Accepted

### Is it possible to find the key for AES ECB if I have a list of plaintext and corresponding ciphertext?

Assume I have a list of plaintext text and its corresponding ciphertext which was created using a specific key with AES in ECB mode. Can I recover that key? No. This is what is referred to as a ...
• 478

### How can C rand() be exploited if a secure seed is used?

I once played this online game, it was an old-school MUD. You log in, chat, kill some goblins. It had a casino. You go into the casino and you bet X gold, and there was a 40% chance you win double ...
• 241
Accepted

### SHA-1 collisions - what about practical attacks?

The question asks how a collision in a hash such as SHA-1 could become a practical concern, with focus on the case of a public-key certificate à la X.509. I'll first give an example involving ...
• 122k

### Is there a downside to encrypting too much data with the same key?

Yes, but the answer is more or less embedded in the question here; you can only say that you encrypt too much data in case the secret key and / or plaintext becomes vulnerable. Most modes of ...
• 84.5k
Accepted

### Does having a hash of a password jeopardize the security of plaintext that was encrypted with that password?

Does having a hash of a password jeopardize the security of plaintext that was encrypted with that password? As usual in password-based cryptography, we'll consider that the password was chosen from ...
• 122k

### Many time pad attack (XOR)

A character is usually encoded as an ASCII. This means that it uses up one byte. That's a number from $0 - 255$. It can be represented as a hexadecimal $\text{0x00} - \text{0xFF}$. All your operations ...
• 667

### What are the dangers of using CPU clock drift for generating random data?

A TRNG is never used instead of a CSPRNG. They serve different purposes. A TRNG is used to seed a CSPRNG. A CSPRNG alone isn't enough to generate random data since it's reproducible. A hardware ...
Accepted

### What are the implications of a non “constant time” implementations on trusted systems in a non-network scenario?

"Constant-time" is about not leaking information through timing-based side-channels. If you assume that there is no side-channel, then, in particular, there is no side-channel attack. It is ...
• 84.5k

### How does the ROCA attack work?

In the ROCA paper the authors define an integer $M$ (which they call a primorial) as follows: $$M = \prod_{i=1}^{n} P_i = 2 * 3 * ... * P_n$$ Said another way, $M$ is the product of the first $n$ ...
• 3,952
Accepted

### Does blinding work against side channel on RSA?

Blinding protects against some side-channel attacks in RSA: those that target variations in the timing or other side-channel information as a known function of $C$ (or $C^d\bmod n$ should that end up ...
• 122k
Accepted

• 11.6k

### Which attacks are possible against raw/textbook NTRU encryption?

Without a well-designed padding system it may be possible to craft a ciphertext that the decryptor may or may not be able to decrypt properly. Whether the decryptor is able to do so will depend on the ...
• 131k
There are $2^{256}$ different AES keys, the chance that you hit the one right one on first try is thus $2^{-256}=\frac1{2^{256}}$. To put this into perspective, here's a list of events that is ...