Public key encryption has been around since the late sixties and it has benefited the world immensely. It has helped promote e-commerce, making transactions secure and it has enabled people across the world to communicate privately. However with the imminent invention of viable quantum computer systems, public key encryption will be obsolete. As society is now so reliant on the ability to communicate securely, there will be a desperate need to fill this void; quantum encryption techniques need to be developed that are immune to the abilities of a quantum 'code-breakers'. We do however have plenty of time and although PKE's days are numbered, this number is very, very large.

Quantum Computing

Quantum computers where first proposed in the 1970s and 1980’s⁸ and researchers has been ongoing ever since. They use particles (electrons, photons, nuclei) to represent states in a computer system and manipulate these particles to perform calculations. A quantum particle can exist in the two classical states of 0 and 1 and also in both state 0 and state 1 at the same time. This allows quantum particles to represent more than one piece of information at once. Quantum bits or qubits can also be joined together on the atomic scale; once they are joined they can share information at the speed of light. This ability to share information means that quantum computers can perform calculations in a highly parallel, non-linear fashion1; unfortunately this makes them very suitable and highly capable of computing algorithms for key decryption in a fraction of the time a "conventional computer" would require. If a quantum computer can decrypt a communication in a "reasonable" time-frame (i.e. days rather than millennia) then the communication cannot be deemed safe. This is a distant problem; to decrypt a public key, a Qubit is needed for each bit in the public key⁹ (i.e. a 1024 bit encryption key would need a quantum computer with a 1024 qubit processor). One of the most advanced quantum computers in the world has only 5 qubits (IBM) and this number doesn’t seem to be rising with any significant pace. Therefore it will be many years (probably two or more decades) before quantum computers become a threat to public key encryption, but their effects need to be looked at and discussed now.

Alternatives to Public Key Encryption

Very important data cannot be "too secure" and however infeasible it is to suggest that a public key encrypted file could be "cracked" it is possible; new and completely secure techniques need to be developed for such data. One popular technique is light encryption, where light transmitted down a fibre optic cable is altered in a way only known by the sender and receiver. Currently multiple researchers are working on ways to polarise light to achieve this aim.¹⁰ The quantum uncertainty principle states that a quantum objects cannot be observed without changing them¹¹, therefore if there is a third person ("Eve") who wishes to intercept a transmission they will change the transmission. This change will corrupt the delivered message and the receiver ("Bob") will then be alerted to the interception. Further more the person wishing to intercept the message will not know which way the light particles are polarised (they obviously observe them) so they will only get part of the message, which would be useless. It is in fact a physical impossibility to accurately intercept and understand the message . This technique has obvious uses in the future when decryption of public keys will be easier, but it has equally useful uses at present. Information can very easily be intercepted at present and although this information is useless (because of its high level of encryption) there is nothing preventing its storage. This information could then be decrypted when better technology becomes available. This is acceptable if the stored information was bank details from decades ago, but if it were the precise method of making a nuclear weapon it could be devastating. This technology is however very close and within the next five to ten years it will probably be widespread amongst government agencies.

What's next for Public Key Encryption

Public Key Encryption does have many years left and at the moment it is more than secure enough for most of our needs. It took a group several months to "crack" a 512 bit key using a distributed network of thousands of machines and therefore it is only possible to "crack" three or four messages a year. Further to this is the fact at increasing the key size exponentially increases the time taken to "crack". Therefore a 1024bit code (not terribly infeasible to encode and decode) would take vastly more time to "crack" than a 512bit code. There are some problems with increasing the key size however; every time you double the key size, the amount of time taken to encode/decode is increase by a factor of 62. Therefore if the key size increases at a steady rate, (to maintain the same level of protection) then the amount of resources devoted to encryption will also have to increase. At some point it will become un-affordable to have the amount of processor power needed to send or receive messages and at this point Public Key Encryption will be at the end of its useful life.