Symmetric Encryption

• Both sides share a secret (key).

Cleartext

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We implicitly distinguish between the algorithm and the key:

- the algorithm is constant and known.

- Safety is in the knowledge of the key.

Encryption:

Transforming information using a secret (a key) for hiding it in a way that it can not be reconstructed without this secret (this key)

Breaking:

Reconstructing the original information without known the key:

- Finding the key K (or part of it)

- Reconstructing the ClearText or part of it.

- Distinguishing between the CipherText and random data.