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The word Cryptography is a word made up from greek etymology: “Kryptos” means hidden, and “graphia”, which means writing. Cryptography is a technique created to deal with the protection of confidential information from unauthorized observers. This means, only an observer with the knowledge to solve the code could get the information.

Through cryptography, information can be protected against unauthorized access, interception, modification, and the insertion of extra information. It can also be applied to prevent unauthorized access and use of the resources of a network or computer system and to avoid users from denying the services to which they are allowed. Modern cryptography includes all the methodologies to provide the security of telematic networks, including the identification, authentication, control of resources, and the privacy and integrity of confidential messages.


 The beginnings of cryptography go centuries ago. Until recent decades, it has been the history of classical cryptography – encryption methods that use pencil and paper, or perhaps simple mechanical aid. At the beginning of the 20th century, the invention of complex mechanical and electromechanical machines, such as the Enigma rotor machine, allowed the creation of more sophisticated and efficient encryption methods; and the subsequent introduction of electronics and computing has allowed elaborate systems that remain highly complex.

picture of quantum computing concept with green light surrounding

Quantum Mechanics in Cryptography

Quantum cryptography is cryptography that uses principles of quantum mechanics to guarantee the absolute confidentiality of transmitted information. Quantum cryptography as an idea was proposed in 1970, but it was not until 1984 that the first protocol was published. One of the most crucial properties of quantum cryptography is that if a third party attempts to spy during the creation of the secret key, the process is disrupted, with the intruder being warned before private information is transmitted.  The security of quantum cryptography rests on the foundations of quantum mechanics, unlike traditional public-key cryptography, which rests on assumptions of the unproven computational complexity of certain mathematical functions.

Quantum cryptography uses photons to transmit a key. Once the key is transmitted, it can be encrypted and unencrypted using the normal secret key method. To convert photons into a key, binary code is used. Each type of photon spin represents information, usually a 1 or 0, for a binary code. This code uses ones and zeros to create a consistent message. An example is the word “h-e-l-l-o” which could correspond to a set of numbers in binary code, let’s say 01101000. Therefore, a binary code can be assigned to each photon, depending on the spin of the current photon. The secret is in applying quantum principles in modern cryptography. This is the basis of the technique known as Quantum Key Distribution (QKD). QKD is not only a solution to computer security problems. It can also secure data exchange. We can make the same sequence of random numbers appear simultaneously in two separate places, without going through the middle. It’s like it’s magic, but it’s something quantum physics predicts.

Quantum Computing shown using zeros and ones in a blue and green light

Quantum Cryptography Challenges

In practice, quantum cryptography has its weakness. It has been recognized, for example, that a hacker could blind a detector with a strong pulse, preventing it from seeing the photons that held the secret. Photons are typically generated by a laser at such a low intensity that it produces only one photon at a time. And there is always a small probability that the laser could emit a photon encoded with confidential information and then a second photon with the information repeated. In this case, all the enemy has to do is steal the second photon, and they will have access to the data without us knowing.

Alternatively, it can be tricky to tell when a single photon arrives. The detectors may not register that a particle has hit them, leading us to think that the system has been hacked when it is actually quite safe. If we had better control over quantum systems than we have with today’s technology, perhaps quantum cryptography could be less susceptible to problems. No system is 100% perfect, and even the most advanced technology always deviates from theory in some way. A smart hacker always finds a way to exploit security breaches.

Any encoding method can only be as secure as the humans who make it work. Today no one knows exactly when there will be a quantum computer with sufficient capacity (design and qubits) to override procedures that facilitate security mechanisms in communications and digital networks, typically through the use of cryptography.  The date range is very loose from a few years, for the very optimists, to several decades. It is very clear that it will be difficult for us to have these computers at a particular level in the coming decades, which is a matter that will be restricted to large countries with the economic and scientific capacity to carry this complex project forward.