Not every piece of information is meant for public consumption. While it might be mostly embarrassing if personal love letters are published, state secrets can actually put human lives at risk. One way to protect information is encryption. A pre-defined algorithm transforms a readable text into a cipher, a text that is not readable anymore. The inverse process, going back from an encryption text to a clear text is called decryption. The encryption and decryption process is controlled by a key. If both parties have the appropriate key(s), they can transform the clear text into a cipher and back. ![[encryption.excalidraw.light.svg]] In general, we can distinguish between [[Asymmetric Encryption|asymmetric encryption]], where at least two keys are involved and [[Symmetric Encryption|symmetric encryption]], where the same key is used for en- and decryption. One key challenge for [[Symmetric Encryption|symmetric encryption]] is key distribution. Alice and Bob must agree on the same key, without having a secure connection. A classical solution are [[Key Distribution Algorithms]]. Using quantum technology, we can make use of [[Quantum Key Distribution|quantum key distribution algorithms]]. It is instructive to have a look at easy encryption algorithms like the [[Ceasar Cipher|Caesar chiffre]]. It is a basic substitution of letters for other letters. >[!read]- Further Reading > - S. Singh, _The Code Book: The Science of Secrecy from Ancient Egypt to Quantum Cryptography_, 1. ed (Anchor Books, New York, 2000). > - [[Symmetric Encryption]] > - [[Asymmetric Encryption]] >[!ref]- References