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Let's suppose I take a cipher with key size equal to the block size (Threefish).

I XOR a random block in the ciphertext, encrypt with a key, XOR another random block, encrypt again with another key and XOR a third random block. It would be XOR->Encrypt->XOR->Encrypt->XOR.

/\ Is this scheme vulnerable to Meet-in-the-middle attacks or another kind of attack?

I received an answer in another question saying that a XORed block with an IV when encrypted twice increase security to [block size] * [key size], that's why I'm asking this question.

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  • $\begingroup$ It is not clear where are you heading and what is your aim? What do you want to achieve? Are you looking for securing your disk encryption? This you see XEX, XTS? How the x-ored random blocks are stored per encryption? $\endgroup$
    – kelalaka
    Feb 5, 2022 at 9:14
  • $\begingroup$ @kelalaka I'm planning to write a disk encryption program in the future that will use large keys up to 32768-bits.. I know that this scheme looks like XEX/XTS. This program I'm planning to write will use raw keys and it will be responsibility of the user in keeping them safe. Maybe you think I'm crazy, but i don't care. =) $\endgroup$ Feb 5, 2022 at 22:40
  • $\begingroup$ @kelalaka I would appreciate if you answer my question. $\endgroup$ Feb 5, 2022 at 22:41

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