# Tag Info

5

I am curious which security algorithms are sensitive to an attacker being able to encrypt whatever they choose to (and see the result). No algorithm would be considered secure if they could be broken under that assumption. Also, is there a known guide (or a googleable name) of this property of crypto algorithms? There's a couple of different names (based ...

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This is called a Chosen Plaintext Attack (or CPA for short) where the attacker can obtain the ciphertext for arbitrary plaintext. A modern cipher should be CPA-resistant. For example, AES-CBC with a proper random IV is IND-CPA. But be aware that there are many other types of security levels, CPA is just one of them. You can find a good overview of crypto ...

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Let's consider what you know: you have the last block, the IV, and the entire ciphertext. What you don't know is the key or the plaintext. Since CBC-mode encryption uses the IV directly only with the first block you must find the first block, before the IV even becomes useful for your attack. Since the CBC mode uses AES(plaintext[i] XOR ciphertext[i-1], key) ...

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Usually, the brute-force attack is performed with known-plaintext where a message $m$ and its ciphertext $c = \operatorname{XTEA}(k,m)$ is available. Indeed, one may need more than one to exactly found the key since a key selects permutation and at the point $m$ there can be more than one permutation selected by different keys that maps to the same ...

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The approach in the Heys’ tutorial where the author uses the approach bruteforce last round using every possible keybit [at the output of] active sboxes and trace differentials up to [the output of] $r-1$ rounds is more fundamental because it is more general. One needs to meet in the middle at the output of some round and check which value for the guessed ...

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