Information security is a growing concern in our modern world, where almost everything can be done online. To protect security, classical encryption protocols, such as RSA, are used. These encryption protocols are almost always based on mathematical problems that are computationally difficult. Therefore, the security is only valid under limited computational resources, and is not provably security. For applications with high security requirements, a trusted courier is sometimes used instead, physically carrying a hard drive with keys from one location to another. While not vulnerable to cyber attacks, trusted couriers are vulnerable to physical interception or bribery.
Quantum key distribution (QKD) offers a solution by utilizing quantum mechanics to grow a secure cryptographic key shared between two distant parties. The quantum nature of the particles used in the exchange ensures that any eavesdropper would leave signs of their presence, allowing the users to precisely quantify the security of the key that is produced. In essence, the user can tell if the quantum particles have been intercepted. This allows secure generation of a random key which does not rely on computational assumptions, secure regardless of available computational power, without requiring trusted courier.