‘One of the most famous systems of secure communication was the Green Hornet. During WWII, Winston Churchill had to discuss vital matters with Franklin D. Roosevelt. At first, the calls were made using a voice scrambler as this was thought to be secure. When this was found to be untrue the engineers started work on a whole new system, the Green Hornet or SIGSALY. Anyone listening in would just hear white noise but the conversation was clear to the parties. As secrecy was paramount, the location of the Green Hornet was only known by the people who built it and Winston Churchill, and if anyone did see him entering the room it was kept in, all they would see was the Prime Minister entering a closet labelled ‘Broom Cupboard.’ It is said that because the Green Hornet works by a one-time pad it cannot be beaten.’ (source: Wikipedia)

Green Hornet was one of the first of many encryption schemes that were or are used to protect our messages. Since WWII communication has become much more intense. Nowadays we communicate daily over the internet and most of that communication we don’t want to share with third parties. How can we communicate securely using a quantum internet? Find out in this next lecture by Stephanie.

Main takeaways

• One of the applications of a quantum internet is secure communication. Specifically, a quantum internet allows us to realize quantum key distribution.
• Practical cryptographic systems that are used in the real world nowadays use keys that are much shorter than the message. So they don’t offer the ultimate guarantees of security.
• Qubits cannot be copied, and this is at the heart of quantum key distribution, which always allows us to make more key to secure communication.