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Encryption turns readable data into scrambled code that only someone with the right key can turn back. It protects online banking, card payments and private messages; the padlock many browsers show beside a web address means the page reached you encrypted.

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People have hidden messages for thousands of years. Julius Caesar is said to have shifted each letter a fixed number of places along the alphabet, and in the 9th century the Arab scholar al-Kindi showed how to crack such codes by counting how often each letter appears. Modern encryption rests on mathematical problems that even very fast computers cannot solve without the key. For centuries the hard part was sharing a key safely. In 1976 Whitfield Diffie and Martin Hellman published a way for two strangers to agree on a secret key over an open line, the basis of what is called public-key cryptography; British government mathematicians had found similar ideas in secret a few years earlier. Your browser and your bank use this method, in a fraction of a second, every time you log in.

Türkçe oku
Şifreleme, okunabilir veriyi anlamsız görünen bir karakter dizisine dönüştürür; bu diziyi yalnızca doğru anahtara sahip olan çözebilir. İnternet bankacılığını, kartlı ödemeleri ve özel mesajları bu yöntem korur. Birçok tarayıcının adres çubuğundaki asma kilit simgesi, sayfanın size şifreli ulaştığını gösterir.

İnsanlar mesajlarını binlerce yıldır gizliyor. Anlatıldığına göre Jül Sezar, mektuplarında her harfi alfabede belli sayıda kaydırırdı. 9. yüzyılda Arap bilgin el-Kindî, her harfin ne sıklıkla geçtiğini sayarak bu tür şifrelerin nasıl çözüleceğini gösterdi. Bugünkü şifreleme, en hızlı bilgisayarların bile anahtar olmadan çözemeyeceği matematik problemlerine dayanır. Yüzyıllar boyunca asıl zorluk, anahtarı güvenle paylaşmaktı. 1976'da Whitfield Diffie ile Martin Hellman, birbirini tanımayan iki tarafın herkese açık bir hat üzerinden gizli bir anahtarda anlaşabileceği bir yöntem yayımladı; açık anahtarlı şifreleme bu fikre dayanır. İngiliz hükûmetinin matematikçileri benzer fikirlere birkaç yıl önce gizlice ulaşmıştı. Bankanızın sitesine her girdiğinizde tarayıcınız ve bankanız bu yöntemi saniyenin çok küçük bir bölümünde kullanır.

Sources and further reading

Background reading: Encryption
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WonderHistory

When Neil Armstrong radioed “Houston, Tranquility Base here. The Eagle has landed” on 20 July 1969, his words reached Earth about 1.3 seconds later. Radio waves travel at the speed of light, and the Moon is about 384,000 km (239,000 miles) away.

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The atomic clocks on GPS satellites run about 38 millionths of a second a day faster than clocks on the ground, an effect predicted by Einstein's theories of relativity. Left uncorrected, the drift would put your position out by about 11 km within a single day.

A GPS receiver, such as the one in your phone, works out where it is by timing signals from several satellites orbiting about 20,200 km up. Radio signals travel about 300 metres in a microsecond, a millionth of a second, so even tiny clock errors matter. Relativity pulls the clocks apart in two ways. Special relativity says moving clocks run slow: travelling at almost 4 km a second, the satellite clocks lose about 7 microseconds a day. General relativity says clocks in weaker gravity run fast: high above Earth they gain about 46. The net gain is about 38 microseconds a day. So before launch, each satellite clock is set to run slightly slow, at 10.22999999543 million cycles a second instead of 10.23 million, and in orbit it keeps step with clocks on the ground.

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WonderTechnology

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The experiments were done at the University of California, Berkeley, in Clarke's group; Martinis was his doctoral student and Devoret a postdoctoral researcher. Absolute zero, −273.15 °C, is the lowest temperature possible. At the heart of the circuit was a Josephson junction: two superconductors, metals that carry current with no resistance when very cold, separated by an insulating layer only a few atoms thick. Vast numbers of electrons moved together as if they were one particle. The team saw two signs of quantum behaviour: the circuit escaped from a trapped state by tunnelling, slipping through an energy barrier it could not climb over, and it absorbed microwave energy only in fixed steps, or quanta, as an atom does. Circuits of this kind are now the qubits, the basic units of information, in the superconducting quantum computers built by companies such as Google and IBM.

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Next card in the archiveOrdinary computers store information in bits that are either 0 or 1. Quantum computers use qubits, which can be in a combination of 0 and 1 at once, called a superposition, until they are measured. For certain problems, such as simulating molecules, they could be far faster than any ordinary computer.Read next →