Nicoletta Lanese 妮科萊塔·拉內塞
Since ancient times， people have relied on cryptography， the art of writing and solving coded messages， to keep their secrets secure. In the fifth century， enciphered messages were inscribed on leather or paper and delivered by a human messenger. Today， ciphers help protect our digital data as it zips through the internet. Tomorrow，the field may make yet another leap; with quantum computers on the horizon， cryptographers are tapping the power of physics to produce the most secure ciphers to date.
Rather than physically hiding a message from enemy eyes， cryptography allows two parties to communicate in plain sight but in a language that their adversary cannot read.
To encrypt a message， the sender must manipulate the content using some systematic method， known as an algorithm. The original message， called plaintext， may be scrambled so its letters line up in an unintelligible order or each letter might be replaced with another. The resulting gibberish is known as a ciphertext， according to Crash Course Computer Science.
The specific knowledge needed to revert a ciphertext into plaintext， known as the key， must be kept secret to ensure a message's security. To crack a cipher without its key takes great knowledge and skill.
In the digital era， the goal of cryptography remains the same: to prevent information exchanged between two parties being swiped by an adversary. Computer scientists often refer to the two parties as “Alice and Bob，” fictional entities first introduced in a 1978 article describing a digital encryption method. Alice and Bob are constantly bothered by a pesky eavesdropper named “Eve.”
The advent of computer networks introduced a new problem: if Alice and Bob are located on opposite sides of the globe， how do they share a secret key without Eve snagging it？ Public key cryptography emerged as a solution，according to Khan Academy. The scheme takes advantage of one-way functions — math that is easy to perform but difficult to reverse without key pieces of information. Alice and Bob exchange their ciphertext and a public key under Eve's watchful gaze， but each keep a private key to themselves.
By applying both private keys to the ciphertext，the pair reach a shared solution. Meanwhile， Eve struggles to decipher their sparse clues.
A widely used form of public key cryptography， called RSA encryption， taps into the tricky nature of prime factorization — finding two prime numbers that multiply together to give you a specific solution. Multiplying two prime numbers takes no time at all， but even the fastest computers on Earth can take hundreds of years to reverse the process. Alice selects two numbers upon which to build her encryption key， leaving Eve the futile task of digging up those digits the hard way.
In search of an unbreakable cipher， today's cryptographers are looking to quantum physics. Quantum physics describes the strange behavior of matter at incredibly small scales. Like Schr dinger's famous cat， subatomic particles exist in many states simultaneously. But when the box is opened， the particles snap into one observable state. In the 1970s and '80s， physicists began using this funky property to encrypt secret messages， a method now known as “quantum key distribution.”
Just as keys can be encoded in bytes， physicists now encode keys in the properties of particles， usually photons. A nefarious eavesdropper must measure the particles to steal the key， but any attempt to do so alters the photons' behavior， alerting Alice and Bob to the security breach. This built-in alarm system makes quantum key distribution “provably secure，” Wired reported.
Quantum cryptography is more than an abstract notion. Many companies are now locked in a race to develop quantum cryptography for commercial applications， with some success so far. To guarantee the future of cybersecurity， they may also be in a race against the clock.