If meet in the middle is a known plaintext attack, and i already have both plaintext and ciphertext, why would i need to find the key?

user110859

8/13/24, 11:34 AM

since I already have plaintext and ciphertext why would I need the key for? what purpose would that serve?

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meet-in-the-middle-attack

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Crypto

Morrolan

8/13/24, 12:22 PM

The intuition behind known-plaintext attacks is that often an attacker is able to get encryptions for plaintexts of their choice, but is not aware of all plaintexts which were encrypted with that key. Consider for example an online document editor storing users' documents in an encrypted form. You as an attacker can easily get that service to encrypt whatever plaintext you want by having it store a document of your choice. But you do not yet have any information about other users' documents.

If now a known-plaintext attack allows you to e.g. derive the key, you can use this knowledge to also decrypt all other ciphertexts for which that key had been used.

See e.g. this post and its answers for additional insight into how known-plaintext attacks map to "real" attack scenarios.

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Elon Musk

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EN: If meet in the middle is a known plaintext attack, and i already have both plaintext and ciphertext, why would i need to find the key?

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