世上無人能破解!量子力學為何是最強之盾?量子糾纏不只安全,還能讓你上網超光速!?|量子熊 ✕ 泛科學 EP11

【科科報報】五條科學新知直播
27 May 202415:13

Summary

TLDRThe script delves into the potential threat quantum computers pose to current encryption systems, with estimates suggesting a security breach by 2030. It introduces quantum encryption as a countermeasure, highlighting Taiwan's first quantum-encrypted communication network. The script explains traditional encryption methods like RSA and their vulnerability to quantum attacks, then contrasts this with quantum communication's security, based on the no-cloning theorem and BB84 protocol. It also touches on quantum entanglement's role in secure communication, emphasizing that while it enables instant key comparison, it doesn't facilitate faster-than-light communication.

Takeaways

  • 🛡️ Quantum computers are considered the 'ultimate spear' in technology, posing a significant threat to current encryption systems and information security.
  • ⏰ The Y2Q clock suggests that the threat to current encryption systems could come as early as April 14, 2030, which is earlier than previously estimated by MIT.
  • 🔒 Quantum encryption communication networks, like the one developed in Taiwan by National Science Council and Tsinghua University, are being explored as the 'ultimate shield' against quantum computing threats.
  • 🔐 Traditional encryption methods, such as RSA, rely on complex mathematical problems that are vulnerable to quantum computers' ability to perform factorization quickly.
  • 🤖 The potential impact of quantum computers on information security could extend to personal data, banking information, and even military intelligence between nations.
  • 📬 Quantum communication uses the principles of quantum mechanics to secure data, preventing interception and decryption by unauthorized parties.
  • 🚫 Quantum 'no-cloning theorem' ensures that any attempt to intercept and copy quantum information will inevitably alter the state of the information, making eavesdropping detectable.
  • 🔑 The BB84 protocol, proposed in 1984, is a foundational method for quantum key distribution (QKD), allowing secure communication by comparing reference frames between the sender and receiver.
  • 🌐 The launch of China's 'Micius' satellite demonstrated the feasibility of satellite-based QKD, showcasing the potential for global quantum-secure communication.
  • 🔗 Quantum entanglement, referred to as 'spooky action at a distance' by Einstein, is another quantum phenomenon that can be used for secure communication, forming the basis of the E91 protocol.
  • 🔄 Despite the advanced nature of quantum communication, the actual exchange of keys and information still relies on classical communication channels, ensuring compliance with the laws of physics.

Q & A

  • What is the potential threat posed by quantum computers to current encryption systems?

    -Quantum computers could pose a significant threat to current encryption systems by potentially breaking them much faster than traditional computers. An academic review from MIT in 2019 estimated that by as early as 2035, quantum computers could threaten today's network encryption systems and information security.

  • What is the Y2Q clock and how does it relate to the threat of quantum computers?

    -The Y2Q clock is a reference to a predicted timeline that suggests the 'endgame' for current encryption systems due to quantum computing could be much sooner than previously thought. It suggests that by April 14, 2030, not only personal data like online passwords and browsing habits but also bank deposits and military intelligence could be at risk.

  • Why is it a misconception to think we have a few years to prepare for the threat of quantum computers?

    -The misconception lies in the fact that if data needs to be kept secret for at least 20 years and is encrypted using traditional methods, hackers can store the encrypted information and decrypt it once quantum computers are powerful enough, which could be within a few years rather than decades.

  • What is the concept of 'quantum encryption communication network' and how does it aim to counteract the threat of quantum computers?

    -The concept of a 'quantum encryption communication network' is a system that uses quantum principles to secure communications. It was announced by Taiwan's National Science and Technology Council and Tsinghua University in May 2023 that Taiwan's first quantum encryption communication network has been successfully developed in Hsinchu, aiming to resist the threats posed by quantum computers.

  • How does the BB84 protocol work in the context of quantum key distribution (QKD)?

    -The BB84 protocol, proposed in 1984, is a method for secure communication that uses quantum mechanics to guarantee secure communication. It involves Alice sending single photons with specific polarizations to Bob, who measures them with randomly chosen bases. They later compare their bases, and if they match, the information is confirmed to be secure, thus creating a shared key.

  • What is the significance of the 'no-cloning theorem' in quantum communication?

    -The no-cloning theorem in quantum communication states that it is impossible to make an exact copy of an unknown quantum state. This is significant because it prevents an eavesdropper, like Eve, from intercepting a quantum message, copying it, and then sending it on to the intended recipient without detection.

  • How does quantum entanglement relate to secure communication?

    -Quantum entanglement is a phenomenon where two particles become linked and the state of one instantly influences the state of the other, regardless of the distance between them. This property can be used in quantum communication for secure key distribution, as any attempt to intercept the entangled particles would disturb their state, alerting the communicating parties to a potential breach.

  • What is the E91 protocol and how does it differ from the BB84 protocol?

    -The E91 protocol, proposed in 1991, is another method for quantum key distribution that uses quantum entanglement. Unlike the BB84 protocol, which uses single photons and their polarization states, the E91 protocol relies on the correlation between entangled particles to establish a secure key.

  • What was the significance of the 'Micius' satellite launched by China in 2016?

    -The Micius satellite, launched by China in 2016, was the world's first quantum science experiment satellite. One of its key experiments involved performing quantum key distribution (QKD) using single photons with ground stations, demonstrating the feasibility of satellite-based quantum encryption communication.

  • How does quantum communication ensure the security of transmitted information against potential eavesdroppers?

    -Quantum communication ensures the security of transmitted information by leveraging the principles of quantum mechanics, such as the no-cloning theorem and the observable effects of measurement on quantum states. Any attempt to intercept or measure the quantum states used for communication would disturb those states, alerting the communicating parties to a potential eavesdropper.

  • What are some alternative methods to enhance communication security aside from quantum encryption?

    -Aside from quantum encryption, alternative methods to enhance communication security include biometric authentication, such as iris and fingerprint recognition, which are difficult to replicate. Additionally, using multi-party authentication or distributing data across multiple secure locations can also improve security.

Outlines

00:00

🔒 The Future Threat of Quantum Computers

Quantum computers are seen as the ultimate offensive tool due to their immense computational power, predicted to threaten current encryption systems by 2030. This technological advancement poses significant risks to internet security, banking, and national defense. Current encryption methods may become obsolete, as quantum computers could decrypt stored data in the future. In response, Taiwan has developed its first quantum encryption communication network, aiming to use quantum mechanics for defense against such threats.

05:00

🔒 Quantum Communication: Battling Eavesdropping

Quantum mechanics can counteract eavesdropping by utilizing single-photon communication. When Alice sends a single photon, any interception by Eve would alter the photon's state, making the tampering detectable. The principle of 'quantum no-cloning' ensures that a quantum state cannot be perfectly copied, thus preventing Eve from creating a replica of the intercepted photon. This method significantly enhances the security of communication between Alice and Bob by immediately identifying and stopping any eavesdropping attempts.

10:03

🚀 Advancements in Quantum Key Distribution

The BB84 protocol, developed in 1984, forms the foundation of quantum key distribution (QKD). In 2016, China launched the Mozi satellite to perform QKD experiments from space, proving its feasibility despite challenges like atmospheric absorption. Taiwan has also made strides with a successful QKD network within Hsinchu. Additionally, 'quantum entanglement' allows for ultra-secure communication by ensuring that any change in the entangled particles is instantly detected, though it still relies on classical communication channels for key comparison.

15:04

🔔 Stay Informed with Science Channels

Subscribe to the PanSci and QuBear Quantum Bear channels for more fascinating scientific knowledge and discussions. Activate notifications and join the channel memberships to stay updated on the latest scientific topics and research findings. See you in the next episode!

Mindmap

Keywords

💡Quantum Computer

A quantum computer is a revolutionary computing device that uses the principles of quantum mechanics to process information. It has the potential to solve complex problems much faster than traditional computers. In the context of the video, quantum computers are portrayed as both a 'super weapon' and a 'super threat' due to their ability to break current encryption systems, thus posing a significant challenge to cybersecurity.

💡Quantum Encryption Communication Network

This refers to a network that uses quantum key distribution (QKD) to secure communication. The script mentions Taiwan's first quantum encryption communication network, developed by the National Science Council and Tsinghua University, which aims to counteract the threats posed by quantum computers to traditional encryption methods.

💡RSA Encryption

RSA is a widely used public-key encryption technology named after its inventors, Rivest, Shamir, and Adleman. It is based on the mathematical difficulty of factoring large numbers into primes. The script explains that RSA's security is compromised by the computational power of quantum computers, which can quickly perform the factorization that would take traditional computers an impractical amount of time.

💡Shor's Algorithm

Shor's Algorithm is a quantum algorithm developed by Peter Shor, designed to efficiently solve the prime factorization problem. The script highlights its significance by stating that it can reduce the time required to factorize large numbers, which is a fundamental operation in breaking RSA encryption, from potentially billions of years to just a few minutes on a quantum computer.

💡Quantum Key Distribution (QKD)

QKD is a method for secure communication that uses the principles of quantum mechanics to generate and distribute cryptographic keys. The script describes QKD as the foundation for quantum encryption communication networks, which can theoretically provide unbreakable encryption by detecting any eavesdropping attempts.

💡Eavesdropper (Eve)

In the context of the script, Eve represents a third party who attempts to intercept and decode the communication between two parties, Alice and Bob. The script uses Eve to illustrate the vulnerability of traditional communication methods to interception and the security provided by quantum encryption against such threats.

💡BB84 Protocol

The BB84 protocol is a quantum key distribution scheme proposed by Charles Bennett and Gilles Brassard in 1984. The script mentions this protocol as the basis for modern QKD, which uses the properties of quantum mechanics to ensure that any attempt to eavesdrop on the communication will be detected.

💡Quantum Entanglement

Quantum entanglement is a phenomenon in which two or more particles become correlated in such a way that the state of one particle is dependent on the state of the other, even across large distances. The script discusses the potential of using entangled quantum pairs for secure communication, where the measurement of one entangled particle instantly affects the state of the other.

💡E91 Protocol

The E91 protocol, named after Artur Ekert, is a quantum key distribution method that uses quantum entanglement to establish a secure key between two parties. The script briefly introduces this protocol as an alternative to BB84, leveraging the properties of entanglement to ensure the security of the key distribution process.

💡Quantum Supremacy

Quantum supremacy is the point at which a quantum computer can perform a calculation beyond the capabilities of the most powerful classical computers. While not explicitly mentioned in the script, the concept is implied through the discussion of quantum computers' ability to break traditional encryption much faster than classical computers.

💡Y2Q Clock

The Y2Q Clock is a hypothetical timer mentioned in the script that predicts when quantum computers will be able to break current encryption methods. It symbolizes the urgency and impending threat that quantum computers pose to existing cybersecurity measures.

Highlights

Quantum computers are predicted to threaten current encryption systems by 2035, as per a 2019 academic review from MIT.

The Y2Q clock suggests an even earlier threat to cybersecurity, targeting April 14, 2030.

Hackers can store encrypted data now and decrypt it later when quantum computers are more accessible.

Taiwan's first quantum encryption communication network was announced by National Science and Technology Council and Tsinghua University in May 2023.

Quantum encryption uses the principles of quantum mechanics to secure communication against quantum computing threats.

Traditional encryption methods like RSA are vulnerable due to quantum computers' ability to perform complex mathematical calculations quickly.

Quantum communication relies on the no-cloning theorem, preventing the duplication of quantum states.

The BB84 protocol, proposed in 1984, is the foundation of quantum key distribution (QKD).

China's launch of the quantum satellite 'Micius' in 2016 demonstrated the feasibility of QKD via satellite communication.

Quantum entanglement can be used for secure communication over long distances without the risk of eavesdropping.

The E91 protocol, based on quantum entanglement, was proposed in 1991 for key distribution.

Quantum communication does not allow for faster-than-light communication or violation of causality.

The essence of quantum communication lies in the security of quantum key distribution against quantum computing threats.

Key exchange and message transmission in quantum communication still rely on classical communication channels.

Alternative methods to quantum encryption, such as biometric authentication, are suggested for secure communication.

The potential of third-party or multi-party authentication for enhancing communication security is mentioned.

Transcripts

play00:01

量子電腦是最強的矛

play00:04

那最強的盾呢

play00:05

量子電腦既然是新世代的超級技術

play00:08

那麼也一定會成為超級威脅

play00:10

麻省理工學院

play00:11

2019年的一份學術評論就預估

play00:14

最快2035年

play00:15

量子電腦就足以對現今的網路加密系統

play00:18

和資訊安全產生威脅

play00:20

不過最新的 Y2Q 時鐘

play00:23

更把這個終局時刻大大提前

play00:25

壓在2030年的4月14日

play00:28

到時候不光是你的網路帳密

play00:30

瀏覽內容會曝光

play00:32

你銀行裡的存款

play00:33

甚至國與國之間的軍事情報

play00:36

都將成為被攻擊的目標

play00:38

還好 還有個幾年時間可以準備

play00:41

play00:41

才不是這樣

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如果一份資料起碼要保密 20 年

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用的卻是傳統加密技術

play00:47

就代表駭客可以立刻把加密的資訊囤著

play00:50

等個幾年就能通通解密了耶

play00:52

最強之盾在哪呢

play00:55

既然你用量子力學攻擊我

play00:57

那麼我為什麼不用量子力學來防禦呢

play01:00

2023年5月3日

play01:02

國科會與清華大學召開記者會

play01:05

宣布台灣第一個量子加密通訊網路

play01:07

已經在新竹研發成功了

play01:09

到底這個「量子加密通訊網路」

play01:12

真的能夠抵抗最強的矛嗎

play01:14

量子又要如何拿來通訊呢

play01:58

為什麼現在的資安在量子電腦前

play02:01

會薄弱的像一張紙呢

play02:03

這就得先問

play02:04

我們現在的資訊安全是怎麼來的

play02:07

每當我們在網站上輸入帳號密碼

play02:10

並且將資料傳送到另一端的電腦

play02:12

就能成功登入

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但這也代表

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管理帳號密碼資料庫的人

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甚至是管理中間通訊的業者

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都可能染指你的機密資料

play02:21

因此 我們開發出了「加密」技術

play02:24

簡單來說

play02:25

就是彼此之間的溝通都使用暗號

play02:28

只有知道如何解讀暗號的雙方

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才能破譯出真正正確的訊息

play02:33

加密的方法很多

play02:35

我們以當今最普及的加密演算法

play02:37

RSA為例

play02:38

它是一種非對稱密碼學

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密碼學家設計了一套數學公式

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可以讓每個人打造出兩把鑰匙

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公鑰與私鑰

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公鑰可以分享給大家

play02:49

私鑰則要留在自己身上

play02:51

當有人想要傳訊息給你

play02:53

可以通過公鑰來上鎖

play02:55

上鎖後的訊息

play02:56

就只有私鑰可以解開

play02:58

這樣一來 任何人都可以傳加密訊息

play03:01

但只有你能解讀訊息

play03:04

然而 如果有人攔截加密過後的資訊

play03:07

即使沒有私鑰

play03:08

實際上還是有辦法破解的

play03:10

因為本質上 RSA加密的核心概念

play03:13

就是將一組質數

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重新設計為公鑰與私鑰

play03:18

並且與需要加密的資訊相乘

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得到一個複雜、難解的超大數字

play03:23

只要駭客能推斷出公鑰中公開的大數字

play03:27

是哪兩個數字相乘

play03:29

那麼就能成功解密出訊息

play03:31

這不難對吧?

play03:32

聽起來就只是做質因數分解

play03:35

等等

play03:35

現今的金鑰大多使用300多位數的質數

play03:39

也就是 如果你想要嘗試破解密碼

play03:42

就相當於要對一串600多位數的超長數字

play03:46

進行「質因數分解」

play03:48

用傳統電腦來處理這類的問題

play03:50

需要耗費數千萬年、甚至上億年

play03:54

但量子電腦出現了

play03:56

我們在之前這一集

play03:57

就已經展現過它特別強大的運算力

play04:00

利用特別為量子電腦開發的「秀爾演算法」

play04:03

就能將傳統電腦

play04:05

要耗上數千萬、數億年

play04:07

才能解決的質因數難題

play04:09

壓縮到一分鐘以內

play04:11

當然

play04:12

在網路、金融、甚至軍事等現實應用中

play04:15

加密的方式更加複雜

play04:17

但本質上

play04:18

都是利用更加複雜

play04:19

更加龐大的數字與數學計算

play04:21

來防止駭客破解

play04:23

但顯然 要跟量子電腦比數學

play04:26

已經證明就像以卵擊石

play04:28

完全沒有勝算

play04:29

這件事可非同小可

play04:31

密碼被破解

play04:32

不只是你的密碼外洩那麼簡單

play04:34

更可能影響到一個國家的安全

play04:37

電影《模仿遊戲》中

play04:38

班奈狄克主演的電腦科學之父艾倫·圖靈

play04:41

就是因為在二戰期間

play04:43

成功破譯納粹德國的軍事密碼

play04:46

讓同盟軍在許多戰役取得先機

play04:49

並獲得勝利

play04:50

但為了不被破解

play04:51

我們應該設計更難

play04:53

位數無上限的質數或密碼來對抗嗎

play04:56

在量子力學之前耍大刀

play04:58

這顯然不切實際

play05:00

不過解鈴還須繫鈴人

play05:02

量子電腦釋放的惡魔

play05:04

就用量子力學來封印吧

play05:08

在密碼學中 我們會將傳訊息的雙方

play05:11

定為Alice 跟 Bob

play05:13

Alice 永遠都需要傳訊息給 Bob

play05:16

不要問我為什麼

play05:17

這就像笑話中

play05:18

為什麼受傷的都是小明或阿寶一樣

play05:21

而 Alice 和 Bob 以外的第三者

play05:24

我是說心懷不軌

play05:25

來偷取訊息的駭客 則叫做 Eve

play05:28

那為什麼不是C開頭的

play05:30

什麼 Cindy 或 Clare 呢

play05:32

是因為竊聽者的英文叫做 eavesdropper

play05:35

所以簡稱 Eve

play05:36

總之

play05:36

這三位是密碼學言情小說中的固定班底了

play05:40

麻煩的是

play05:41

當 Alice 打了一通電話給 Bob

play05:43

這時候手機的訊號

play05:45

會藉由電磁波在手機和基地台之間傳遞

play05:48

而 Eve 神不知鬼不覺地竊聽

play05:51

偷偷接收了一段電磁波

play05:53

想必不會有任何人發現

play05:55

要對抗 Eve 只剩下唯一的辦法

play05:58

就是利用量子力學的神奇力量

play06:00

讓 Eve 拿不到這些訊息

play06:06

量子力學是如何對抗竊聽者Eve的呢

play06:09

既然傳統的通訊方式

play06:11

是因為能被攔截所以會被破解

play06:14

那麼你應該也想到了

play06:15

那就不要被攔截不就好了嗎

play06:17

沒有錯 雖然聽起來像是廢話

play06:20

但卻也正是「量子通訊」的核心思想

play06:23

單光子通訊

play06:24

我們在第一季的量子系列中有提到

play06:27

不只有物質能表現得像波

play06:29

波也能表現得像是粒子

play06:32

一段段的電磁波

play06:33

也能視為一顆顆的光子

play06:35

在傳統通訊中 每次的電磁波通訊

play06:38

都像是億萬顆的光子

play06:40

難怪被截取了一部分

play06:42

也絕對沒有人會發現

play06:44

但假如今天 Alice 送出的信件

play06:46

就是送出的光子只有一個

play06:49

那麼一旦 Bob 沒有收到

play06:51

就能肯定中途是被攔截了

play06:53

因此 只要將加密訊息拆成數段

play06:56

一旦發現內鬼就終止交易

play06:58

或是馬上換另一種加密方式

play07:01

就能有效防止「竊聽」的發生

play07:03

那你說 Eve 也沒有那麼傻

play07:05

從 Alice 那邊攔截了一顆光子

play07:08

那就再傳另外一顆一模一樣的光子

play07:10

給 Bob 不就好了嗎

play07:11

就像是 Eve 中途把郵差的信封

play07:14

偷偷拆開來看

play07:15

看了一下裡面的內容後

play07:17

再原封不動地將信封黏放回去

play07:19

如此一來

play07:20

Alice 或 Bob 應該也不會察覺異狀吧?

play07:23

確實

play07:24

傳統通訊方式就是吃了這樣的虧

play07:27

所以才頻繁被 Eve 得逞

play07:29

然而量子資訊裡面

play07:30

有一條鐵律解決了這個問題

play07:33

那就是「不可複製原理」

play07:35

指的是人們不可能「複製」出

play07:37

一模一樣的量子態

play07:39

為什麼呢

play07:40

因為在量子力學中

play07:41

「測量」就會讓波函數塌縮、影響結果

play07:44

而這件事是不可逆的

play07:46

簡單來說 薛丁格的箱子一被打開

play07:49

就只有貓死或貓活的其中一種狀態

play07:53

就算重新把蓋子蓋上

play07:55

活的貓就還是活的貓

play07:57

你無法再還原出一模一樣

play07:59

貓死跟貓活兩個狀態同時存在的箱子了

play08:02

你可能想問

play08:03

為什麼不能做出一樣的箱子呢

play08:05

我們直接用光子來舉例吧

play08:07

光的身上帶有一個特性

play08:09

叫做「偏振」

play08:10

例如在液晶螢幕中

play08:12

可以透過液晶設計一種特殊柵欄

play08:15

允許特定方向的偏振光通過

play08:17

藉此控制光線的開跟關

play08:20

光子身上也帶有偏振

play08:22

我們讓 Alice 設計四種可能的狀態

play08:25

垂直偏振、水平偏振

play08:27

以及兩種斜向的偏振

play08:29

分別代表兩組的0與1

play08:32

接收端則準備兩種偏振檢測器

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分別針對直角和對角方向

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這兩種柵門被稱為「基」(basis)

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接下來要做的

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就是設法讓光子通過

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假設 Alice

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發射了一顆垂直偏振的光子

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代表訊號0

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而Eve也準備了直角的基

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那麼 Eve 就能準確地偵測出

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這顆光子百分之百偏振是垂直的

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但如果 Eve 要接收這顆光子

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卻準備了錯誤的基

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例如選成了對角向的柵門

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這時候 Eve 還是能檢測出訊號

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但是它不會檢測出垂直偏振的訊息

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而是有一半的機率

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觀測到光子是右上左下的偏振

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解讀出0

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卻也有一半的機率

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觀測到光子是左上右下的偏振

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而解讀出1

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但因為 Eve 已經打開了薛丁格的箱子

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因此他全然不知道自己

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已經因為用上錯誤的方法觀察

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而獲得錯誤的資訊

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通訊過程中

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Alice 會先隨機選出位元與基

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Bob 在事前

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不知道 Alice 傳送光子的偏振方式下

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也隨機選了幾種基

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來接收 Alice 傳來的光子

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最後

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Alice 再和 Bob 比對彼此選用的基

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如果兩人選用的基相同

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那麼Bob收到的資訊就一定是正確的

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而這一組基 就相當於密鑰

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加密協定也就完成了

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而使用對角向基的 Eve

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完全無法確定 Alice 傳的訊息

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會不會是垂直或水平的

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因此即使捏造一個訊息傳給 Bob

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最終 Alice 和 Bob 兩人

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一經過比對發現位元怪怪的

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就會發現有內鬼而終止交易

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重新開啟另一個通訊管道、重新加密

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而 Eve 得到的也是錯誤的訊息

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這個方式是由兩位姓氏 “B”開頭的科學家

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在1984年提出的

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因此 被稱為「BB84協定」

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是當今「量子密鑰分發」

play10:25

QKD 的發展基礎

play10:27

那麼 這項技術發展得如何呢

play10:32

2016年

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中國發射了世界上第一顆

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量子科學實驗衛星「墨子號」

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其中一個實驗

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就是透過「單一光子」

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與地面進行QKD量子金鑰分發

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這個實驗並不簡單

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因為衛星在軌道上是高速移動的

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要讓光子能精確打到地面的接收站

play10:51

這個難度啊

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相當於在50公里外

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把一枚硬幣

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投進高速火車中的一個礦泉水瓶子裡

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實驗證明 這方法可行

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已經確實能通過通訊衛星

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來做到量子加密通訊

play11:05

只不過雖然單光子的通訊

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能有效避免監聽

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但因為光子大部分都會被大氣吸收

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因此需要每秒將百萬個光子發射出去

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只求一顆成功到達地面的接收站

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就足夠了

play11:18

除了中國之外

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數個歐美國家

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在開發手邊的量子電腦之餘

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也陸續著手開發量子加密通訊技術

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與之抗衡

play11:26

台灣呢

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以清華大學為主的研究團隊

play11:29

也在2023年5月

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宣布開發出了第一個量子加密通訊網路

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從清大的機房透過雷射與光纖

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將量子加密資訊

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傳到1、2公里外的校內與交大實驗室

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以及10公里外的竹北

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為國內的量子通訊技術當破風手

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但也別忘了

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除了利用單光子通訊外

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量子力學還有一個現象

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適合用來超遠距離的資訊傳遞

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那就是「量子纏結」

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我們在之前的影片

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介紹過這個就連愛因斯坦

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都稱之為「鬼魅般的超距作用」

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在量子通訊中

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我們通常會選用正交偏振態的光子對

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來進行通訊

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舉個例子

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如果 Alice 跟 Bob

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都選擇水平/垂直基

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並且各持有纏結量子對的其中一顆

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如果 Alice 量測到的光子是水平偏振

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那麼 Bob 量測到的

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將100%會是垂直偏振

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也就是說

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彼此一定會測量到相異的狀態

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而這個過程將不受距離影響

play12:29

如果使用纏結的量子對來打造加密系統

play12:32

那麼 Alice 跟 Bob

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只要比較兩人收到的結果

play12:36

而且確定兩人收到的量子位元資訊

play12:38

都恰好相反

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就可以確保中間沒有 Eve 的存在

play12:42

而這個在1991年提出

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以量子纏結為出發點的密鑰分發方式

play12:47

被稱為「E91協定」

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當然還有許多技術性細節

play12:52

不過我們這裡就先省略了

play12:54

但是你一定想問

play12:56

使用量子纏結的加密

play12:58

不就能實現遠距離瞬間通訊嗎

play13:01

這樣就算我跟三體人溝通

play13:03

也不用擔心延遲了嗎

play13:05

這不合理啊

play13:06

愛因斯坦也這樣覺得

play13:08

所以它才堅決否認這種詭異的特性

play13:11

提出EPR悖論

play13:13

想知道EPR悖論是什麼的

play13:14

可以來複習這一集

play13:16

現在的科學家認為

play13:18

雖然量子纏結這個現象確實存在

play13:20

也確實有一種「超距作用」

play13:23

但重點在於

play13:24

「訊息」本身並不是

play13:26

也並沒有透過這種纏結效應傳遞

play13:29

例如 Alice 與 Bob

play13:30

還是得互相比較兩人間的密鑰

play13:33

才能確認彼此間的訊息是否正確

play13:36

那這個過程呢

play13:37

他們終究還是得打一通電話

play13:39

或是透過光纖網路

play13:41

來交換比對被加密的資訊

play13:43

也就是完成「通訊」的過程

play13:45

依舊是在「古典通道」中進行

play13:48

並沒有超光速

play13:49

也不會違背物理學的因果律

play13:51

所以 量子通訊的神奇之處

play13:54

終究和量子計算一樣

play13:56

在於「粒子」本身的疊加態

play13:58

與隨機性、以及量子資訊的不可複製原理

play14:01

它並不是真的透過「超距作用」來「通訊」

play14:05

而是透過「量子效應」來「加密」

play14:07

藉由奇妙、高效的量子密鑰分發

play14:10

讓通訊雙方手中的「密鑰」

play14:12

有所保障、並杜絕了被竊聽的可能性

play14:15

避免量子電腦

play14:17

透過暴力破解來讓傳統加密失效

play14:20

這才是量子通訊的精華所在

play14:22

至於交換密鑰、傳遞訊息的管道

play14:25

依然沿用現今的通訊方式

play14:27

在古典通道中進行

play14:29

所以完全不用擔心

play14:30

你的訊息會因為超光速而穿越時空

play14:37

是的

play14:38

我的主

play14:39

計畫繼續進行

play14:41

除了今天介紹的量子加密法之外

play14:43

你覺得還有哪種方式

play14:45

可以讓通訊不被破解呢

play14:47

像是生物認證

play14:49

例如虹膜跟指紋

play14:51

總不會被人複製吧?

play14:52

還是覺得

play14:53

用第三方或更多方認證

play14:56

把雞蛋分到更多不同的籃子裡呢

play14:58

或是你有其他想法

play15:00

請留言告訴我們吧

play15:01

好的 以上就是本集的內容

play15:03

記得訂閱 PanSci 泛科學頻道

play15:05

跟 QuBear 量子熊頻道

play15:07

開啟小鈴鐺 加入頻道會員

play15:09

鎖定更多精彩的科學新知、科學議題

play15:11

我們下集再見

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