Tag Info

Hot answers tagged

10

XXTEA (also known as Corrected Block TEA) is a block cipher with $128$-bit key and block width parameterizable to $n\cdot32$ bits for $n\ge2$. It is an Unbalanced Feistel Cipher making $q=6+\lfloor52/n\rfloor$ passes over the block, with $q\cdot n$ rounds each modifying $32$ bits of the block. In Cryptanalysis of XXTEA, it is presented a chosen-plaintext ...


10

These aren't "attacks" in and of themselves, they are simply a way to classify attacks depending on how many assumptions they make. For instance, if an attack requires plaintext-ciphertext pairs to recover the key, but they don't have to be any particular pairs, that attack is categorized as a known-plaintext attack. However if another attack required the ...


9

CBC mode encryption is defined as: $C_i = E_k(P_i\oplus C_{i-1})$ (with $P_i$ being the $i$th plaintext block, and $C_{i-1}, C_i$ being the ciphertext blocks. What might happen if we have a lot of ciphertext encrypted with the same key is if two ciphertexts happen to be the same, that is: $C_i = C_j$ If we see that, we can then immediately deduce that: ...


7

The XXTEA cipher is badly broken. Even though the paper is not published at a conference, the author verified it on reduced versions of XXTEA. You should never ever use a cipher or a hash function, that has been broken in academic terms, in particular if you are not a cryptographer. Attacks always get better, and a cipher does not attract much attention ...


6

It seems to me that what you need is a public-key signature scheme like rsa signatures. The process would work something like this: A user license $L$ is created by your license generator Your system signs it to give $s(L)$ and the licence is $\{L,s(L)\}$. When program tries to open the user's license $\{t,v\}$: The system verifies that $v$ is indeed ...


5

Yes, $E$ will be always be secure. This follows from a standard type of proof called a hybrid argument. Giving the full details would be tedious, so here is a sketch in case you are familiar with hybrid arguments: We define games $H_0,H_1,H_2$. We let $H_0$ be the IND-CPA game, but with the game's secret bit hardcoded to $0$. So the game always outputs ...


3

If you can read the intermediate states of the encryption algorithm you could recover, one by one all the round keys. Given a AES round, all the operation between the two AddRoundKey (at the beginning and the ond of the round) are invertible. Take for example round 1: you get the internal state before AddRoundKey (of round 2), you get back at the beginning ...


2

ICE is a block cipher operating on 64-bit data blocks (which is a bit dated, and less than perfectly safe in some usage scenario involving a huge amount of data). Depending on implementations, the key can be 64-bit (which is quite dated, and unsafe against a potent attacker), or some higher multiple (128-bit is fine for longer than I dare try making ...


2

First off, your definition is not IND-CPA: In the IND-CPA setting, the adversary has access to an encryption oracle. As you have already determined, no deterministic encryption scheme can be IND-CPA secure. I don't think IND-CPA is widely used for symmetric encryption though (although I might be wrong), semantic security might be a better option. For public ...


1

The difference is how the plaintext-ciphertext pairs that the attacker has access to are generated. In a chosen plaintext attack, the attacker chooses some plaintext and is handed the corresponding ciphertext. In other words, the attacker may encrypt arbitrary messages. In a chosen ciphertext attack, the attacker can additionally (a chosen ciphertext ...


1

If we try to make an equivalent to these terms in intuitive cryptography (before its formalization into games became the norm) In an eavesdropper attack, the assumption is that an adversary only intercepts a single ciphertext for any given key (and, perhaps, knows the plaintext except for a small portion). In a multiple messages attack, the assumption is ...



Only top voted, non community-wiki answers of a minimum length are eligible