how to find an encryption function when given a plain text and a cipher text?

Answer 1

This problem does not arise in practice. All codebreakers assume that by means of carelessness, or a spy, or a traitor, or bribery, or threats, the actual function or METHOD of encryption will become perfectly well known to them. Their challenge will be to deduce the KEY which has been used to encrypt this particular message.

The uselessness of a cryptosystem whose security lies partly or wholly in the obscurity of its METHOD was first stated by Auguste Kerckhoffs in 1883 ("La Cryptographie Militaire") and has never been challenged since. It is absolutely fundamental.

So, to find the encryption function, either wait for a security lapse, or utilise a spy, a traitor, bribery, or threats. After that will come the difficult bit.

If you are beginning an interest in cryptography, the book I have cited below is an almost indispensable introduction.

Answer 2

Forgive me for stating this yet isn't the factor of project Euler to come to a decision the answer on your individual? nonetheless, do you have a uncomplicated thought approximately a thank you to handle this situation? What did you attempt so some distance? What i could do is attempt each and every password (there are 17576 opportunities), decode the message using the password, then stick to a attempt to guess how possibly the decoded message is written in straightforward english. you're able to get a message that is composed regularly of the characters sixty 5(A) - 122(z) it would incorporate loads of 32 (area) the main established characters could be e, t, a, o, i, n, s, in that order. word each and every password that features a message that's maximum possibly to be the wonderful straightforward textual content cloth. Then leaf in the direction of the outcomes for the wonderful one.

Answer 3

You cannot.
Even if you find an encryption function that works for your samples, it is not guaranteed to be the same as any other cypher in use.

Answer 4

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