Would it be beneficial when trying to decrypt network traffic, to while sniffing on the network, if target sends known file, can this help solve dcrpt

Question

If a known file is sent from on network computer to yourself, or to some other network computer, is there a way this can be leveraged to solve decryption?

Answer 1

So I'm reading your question as "if I have both the ciphertext and the plaintext of a given message, can I use this info to infer the key?"

Practically, no, probably not, unless the encryption system in use is very old (and it helps if the keys are short as well).

For any reasonably encryption scheme, you definitely cannot infer the key if the message is shorter than or exactly the same length as the key itself. Its mathematically impossible by itself, unless you have a very large number of samples.

in the case of a very long message, much longer than the key, the algorithm may become subject to plain-text analysis if its source of randomness is not sufficiently uniformly distributed. This combines two vulnerabilities in the One-Time Pad (key reuse, and poor randomization), and could conceivably make an algorithm vulnerable.

All that said, of course, practical attacks on a "modern" algorithm in the real world are unlikely, and those that succeed are more likely to be vulnerabilities in the software implementing the particular algorithm, in adjacent tasks like key generation/use or exchange, or via sloppy opsec practices. crypto analysis isn't really even on the list of options, except perhaps for very old algorithms that used short keys.