????上周在有關于莫斯科的新聞中，最熱門的話題依然是圍繞著美國的“泄密者”斯諾登，他目前正尋求在俄羅斯臨時避難。與此同時，在這座城市的另一邊，尼古拉斯?吉新博士上周宣布，他找到了能夠防止類似美國國家安全局（National Security Agency）的機構再次窺探公民隱私的辦法。以后的數據加密法將無法攻破、無懈可擊。

????吉新是一名瑞士量子物理學家，他在探索和研究原子和光子等微觀物理問題上走在世界前列。（光子是光的基本粒子。）早在2001年，吉新就與其他人共同創辦了一家名叫ID Quantique 的公司，希望借此把他在量子物理世界里發現的各種奇特現象應用到商業世界中。當年量子學界基本上還處理在純理論階段，在實踐上基本還處于空白，更多地只是在實驗室里進行研究，而不是應用于真實世界。但是在過去十年里，量子技術已經大大地成熟起來，而且已經可以給現實世界帶來很多實際的好處，其中就包括ID Quantique公司目前提供給各大銀行和政府的數據加密技術——這也是一種幾乎不可能被攻破的加密技術。

????吉新說：“這種新技術聽起來似乎像是一種量子物理學的魔法，不過它當然不是魔法，只是一種非常現代化的科學技術?！辈贿^與經典的通訊和加密方法相比，它的確具有某種“魔力”。經典密碼學通常依賴某種數學算法，隨機生成解密密鑰，使信息發送者最終發送出一條加密信息，然后接收者可以通過解密密鑰將信息還原。如果有某個第三方（在數據安全界的術語里稱之為“敵方”）獲取了密鑰的拷貝，那么它就可以獲取這份信息的拷貝，然后破譯它——或者也可以憑借足夠的時間和強大的計算能力，利用強大的算法攻破解密密鑰。（據說美國國家安全局和世界上其他情報機構都是這樣做的。）但是吉新的量子加密技術利用了量子物理學的某些奇特現象，可以使傳送中的密鑰無法被人拷貝，也無法被偷走和破解，除非發送者主動丟棄了這個密鑰。

????ID Quantique公司的量子加密法使用的最主要的量子物理學原理叫“量子糾纏”。它在這種情況下是指兩顆單獨的光子被置于一個相關聯的狀態下。根據量子物理規則，這兩顆糾纏的光子會無可避免地產生相互影響，如果其中一顆光子的狀態被改變了，就必然會影響另一顆的狀態，不管這兩顆光子的位置是遠在天邊還是近在眼前，甚至是分別在地球的兩端。發送者將其中一顆光子發送給接收者，那么發送者和接收者就各擁有了一顆光子。這些光子沒有編入任何有用的信息——需要傳遞的信息還是通過常見的經典加密術加密，但是解密密鑰通過一個隨機數字生成器生成。（真正的隨機數字生成器代表了由量子物理學派生的另一項技術——這個稍后再說）。

????如果敵方要想截獲這個含有密鑰信息的光子，就必須在正確的時刻出現在發送者和接收者之間，但即便做到這一點，他也不能竊取到任何有用的信息。因為根據量子物理學，任何試圖干預傳輸中的量子的行為，都會改變仍然在發送者手中的另一顆糾纏量子的狀態，從而可以向發送者發出警報。這時發送者可以簡單地丟棄掉被攔截的密鑰，然后重新生成一個。

????The news out of Moscow of late has been dominated by Edward Snowden, the American leaker of secret state documents who is currently seeking temporary asylum in Russia. Meanwhile, across town and to much less fanfare, Dr. Nicolas Gisin found himself explaining last week the solution to the very problems of data security and privacy intrusion Snowden brought to light in exposing the vast reach of the National Security Agency's data collection tools: data encryption that is unbreakable now and will remain unbreakable in the future.

????Gisin is a Swiss quantum physicist and a pioneer in the exploration and manipulation of the very small -- that is, the various "quanta" of the micro world, things like individual atoms and photons. (Photons are the elementary particle of light.) In 2001, Gisin co-founded a company called ID Quantique with the aim of converting the strange phenomena found in the quantum world into commercial applications. At that time, the quantum world was still very much a theoretical place, one more suited for the laboratory than employed for practical application. But over the last decade quantum technologies have matured such that they can offer many practical benefits, including the kind of data encryption that ID Quantique now provides to various banks and governments -- data security that is virtually impossible to breach.

????"It sounds like there's some quantum magic in this new technology, but of course it's not magic, it's just very modern science," Gisin says. But next to classical communication and encryption methods, it might as well be magic. Classical cryptography generally relies on algorithms to randomly generate encryption and decryption keys enabling the sender to essentially scramble a message and a receiver to unscramble it at the other end. If a third-party (known as an "adversary" in data security lingo) obtains a copy of the key, that person can make a copy of the transmission and decipher it, or -- with enough time and computing power -- use powerful algorithms to break the decryption key. (This is what the NSA and other agencies around the world are allegedly up to.) But Gisin's quantum magic taps some of the stranger known phenomena of the quantum world to transmit encryption keys that cannot be copied, stolen, or broken without rendering the key useless.

????The primary quantum tool at work in ID Quantique's quantum communication scheme is known as "entanglement," a phenomena in which two particles -- in this case individual photons -- are placed in a correlated state. Under the rules of quantum mechanics, these two entangled photons are inextricably linked; a change to the state of one photon will affect the state of the other, regardless of whether they are right next to each other, in different rooms, or on opposite sides of the planet. One of these entangled photons is sent from sender to receiver, so each possesses a photon. These photons are not encoded with any useful information -- that information is encoded using normal classical encryption methods -- but with a decryption key created by a random number generator. (True random number generators represent another technology enabled by quantum physics -- more on that in a moment.)

????Any adversary would have to place herself in between sender and receiver at just the right moment in order to intercept this key-encoded photon, but even that would not enable her to steal any useful information. Thanks to the laws of quantum mechanics, any tampering with the photon in transit would change the state of the entangled photon still in the sender's possession, raising a red flag. The sender could then simply discard the intercepted key and generate another.