RSA Encryption
RSA Encryption is a popular method to encrypt messages. An example of the fundamentals of this idea can be found in the additional questions.  This article shows a detailed and mathematical derivation of the RSA method.

We have seen that RSA encryption can be effectively broken by using a quantum computer, but we haven’t specified how this exactly works. So how can a quantum computer factor numbers efficiently? This wikipedia article givesan in-depth explanation on Shor’s factoring algorithm, which is the algorithm used for these types of problems.

Ceasar Cipher
Encryption goes way back. Even thousands of years ago people have used forms of encryption to protect their messages. This wikipedia page shows a historical example of encryption: the Ceasar Cipher.

Enigma
Another historical example of encryption was during the second world war. The Germans used a machine called ” Enigma” to encrypt their messages. You might recognize this from the movie “The Imitation Game”. Here is a video on how this machine worked.

Ket notation
In the question in secure communication we used the ket notation. This notation is widely used in quantum computing and quantum mechanics. You can read more about it on the wikipedia of bra-ket notation.

BB84 protocol
We also mentioned the BB84 protocol in the secure communication question. In this video the protocol is discussed, although the animations are a bit perculiar.