# Tag Info

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: ...

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

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 ...

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

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

There exist many standards which describe a lot of padding mode and security protocols. If you're new in that field, I strongly recommand you to study the family of PKCSs standard which are the reference in the domain. There also exist other distinct standards depending of very specific applications fields (Banking, mobile, Cloud, Embedding ... or Global ...

1

Xor can help find bits not yet known, whether most significant or least significant; and help the adversary find more information about both ciphertext and plaintext, especially if a table of potential plain texts or even keys is stored in conjunction with bitwise Xor. Some reading: ...

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 ...

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