密码学与安全百科全书（媒库文选WhatIsCryptography）

Nicoletta Lanese 妮科莱塔·拉内塞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.，接下来我们就来聊聊关于密码学与安全百科全书?以下内容大家不妨参考一二希望能帮到您!

密码学与安全百科全书

Nicoletta Lanese 妮科莱塔·拉内塞

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.

自古以来，人们就依靠密码学这门编写和破解编码信息的技艺来严格保守自己的秘密。公元五世纪，加密信息被写在皮革或纸张上，由信使递送。如今，密码有助于在我们的数字数据快速穿梭于互联网时对其加以保护。未来，这一领域可能再次取得飞跃；随着量子计算机即将问世，密码专家正利用物理学的力量造就迄今为止最安全的密码。

密码学不是在真正意义上让信息躲过敌人的眼睛，而是让双方在敌人眼皮底下联络但使用敌人看不懂的语言。

要加密信息，信息发送者必须利用被称为算法的某种系统性方法来巧妙处理内容。原始信息——叫做明文——可能被彻底打乱，这样一来，字母可能排列成让人无法理解的顺序，或者每个字母可能用另一个字母来替代。按照《计算机科学速成课》（YouTube网站上科普计算机知识的一门课程——本网注）的说法，由此产生的莫名其妙的内容被称为密文。

将密文恢复为明文所需的特定知识——叫做密钥——必须保密，以确保信息的安全。在没有密钥的情况下破译密码需要大量的知识和技巧。

在数字时代，密码学的目标保持不变：防止双方交流的信息被对手窃取。计算机科学家经常把交流信息的双方用“爱丽丝和鲍勃”来指代，这是两个虚构人物，最早出现在1978年一篇描述数字加密法的文章中。爱丽丝和鲍勃时常受到一个名叫“伊芙”的难缠窃听者的烦扰。

计算机网络的出现带来了一个新的问题：如果爱丽丝和鲍勃身处地球两端，他们如何在不被“伊芙”截取的情况下共享一把密钥？汗学院（美国在线教育免费网站——本网注）说，公钥密码体系成为解决问题的一种办法。该方案利用了单向函数——这种数学运算做起来容易，但在没有关键信息的情况下很难进行逆运算。爱丽斯和鲍勃在伊芙警觉的注视下交换密文和公钥，不过两人各自保留了一把私钥。通过将两把私钥运用到密文上，两人就可以取得共用的解法。与此同时，伊芙苦苦破译他们留下的为数不多的线索不得其解。

一种得到广泛应用的公钥密码体系名为RSA加密算法，它利用了质因数分解的妙处——找两个质数，把它们相乘来给出一个明确的解法。两个质数相乘根本花不了什么时间，不过要逆运算，即便是地球上运算速度最快的计算机也要花上几百年。爱丽丝选取两个数字，在此基础上形成她的加密密钥，让伊芙徒劳无功地用笨方法去挖掘这些数字。

为了寻找一种无法破译的密码，如今的密码专家正着眼于量子物理学。量子物理学在小得惊人的尺度上描述物质的奇怪行为。就像薛定谔的那只著名的猫，亚原子粒子同时以多种状态存在。但是当盒子打开时，粒子会一下子变成能观测到的单单一种状态。二十世纪七八十年代，物理学家开始利用这种稀奇古怪的特性来为机密信息加密，这种方法现在被称为“量子密钥分发”。

正如密钥可以用比特编码，物理学家如今用粒子——通常是光子——的特性来给密钥编码。邪恶的窃听者要窃取密钥必须对粒子加以测量，但任何这样做的企图都会改变光子的行为，让爱丽丝和鲍勃警觉到有人试图破坏安全。据《连线》月刊报道，这种自带的警报系统让量子密钥分发具有“可证明的安全性”。

量子密码学不只是一个抽象的概念。许多公司现在都在竞相开发有着商业用途的量子密码体系，迄今为止取得了一些成功。要确保网络安全的未来，这些公司可能也在与时间赛跑。（李凤芹译自美国趣味科学网站6月6日文章）