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Quantum Algorithms

01 /Applications of a Quantum Computer 02 /Breaking encryption 03 /The classical one-time pad 04 /Grover’s algorithm 05 /Quantum fourier transform 06 /Shor's algorithm 07 /Solving linear equations with quantum computers 08 /Quantum Machine Learning 09 /Simulating chemistry 10 /Distributed quantum computing 11 /Quantum Inspire 12 /Deutsch – Jozsa algorithm

The classical one-time pad

Here, Qutech’s Tim Coopmans will introduce the one-time pad, a straightforward, and very secure classical cryptographic protocol. Secure, in this case, means that it is not possible to crack this code if you do not have the ‘key’ that encrypts it. However, this is also the reason that it is not used in practice; both sender and receiver of the communication channel need to have the same key. You will probably later see that there are elaborate quantum algorithms that can ensure just that!

Further Thinking

The one-time pad is not used in practice. One of the reasons for this is because the key needs to be as long as the message that is sent. Why is that? 

As Tim already suggested in the video, can you show on a piece of paper why sending two messages with the same one-time pad is a bad idea?

Can you think of a way we could use a shorter key multiple times?

Solution

Further reading 

In other (quantum) algorithms, you might encounter the classical one-time pad as a reference, so it is useful to understand it. If you want to look at another low-level explanation of this classical algorithm, you can always take a look at the Wikipedia.