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  • Encryption is the process of taking a message and scrambling it's contents so that only

  • certain people can look at your message.

  • There are two types of encryption: symmetric and asymmetric encryption.

  • Let's first take a look at symmetric encryption to understand why asymmetric encryption was

  • created.

  • To do that, let me introduce you to Alice and Bob.

  • Alice has a sensitive document that she wants to share with Bob.

  • She uses an encryption program to protect her document with a password or passphrase

  • that she chooses.

  • She then sends the encrypted document to Bob.

  • However, Bob cannot open this message because he doesn't know the passphrase that Alice

  • used to encrypt the document.

  • In other words: he doesn't have the key to open the lock.

  • Now comes a real problem: how does Alice share this passphrase securely with Bob?

  • Sending it through email is risky because others might find the passphrase and use it

  • to decrypt any messages between Alice and Bob.

  • This is exactly the kind of problem that asymmetric encryption intends to solve.

  • It's compareable to a mailbox on the street.

  • The mailbox is exposed to anyone who knows its location.

  • We can say that the location of the mailbox is completely public.

  • Anyone who knows the address can go to the mailbox and drop in a letter.

  • However, only the owner of the mailbox has a key to open it up and read the messages.

  • Let's go back to technical details.

  • When using asymmetric encryption, both Alice and Bob have to generate a keypair on their

  • computers.

  • A popular and secure way for doing this is by using the RSA algorithm.

  • This algorithm will generate a public and private key that are mathematically linked

  • to each other.

  • Public keys can be used to encrypt data and only the matching private key can be used

  • to decrypt it.

  • Even though the keys are linked together they cannot be derrived from each other.

  • In other words: if you know someone's public key, you cannot derrive his private key.

  • If we retake our mailbox example then the mailbox's address would be the public key

  • something that everyone is allowed to know.

  • The owner of the mailbox is the only one who has the private key and that is needed to

  • open up the mailbox.

  • Let's now take a look at how Alice and Bob can use asymmetric encryption to communicate

  • securely with each other.

  • They start by exchanging their public keys.

  • Bob gives his public key to Alice and Alice gives her public key to Bob.

  • Now Alice can send her sensitive document again.

  • She takes the document and encrypts it with Bob's public key.

  • She then sends the file to Bob, who uses his private key to unlock the document and read

  • it.

  • Because they use asymmetric encryption, only Bob is able to decrypt the message.

  • Not even Alice can decrypt it because she doesn't have Bob's private key.

  • The strength and security of the asymmetric encryption now relies on Alice and Bob to

  • keep their private keys well protected.

  • If an attacker steals Alice's private key, it can be used to decrypt all messages that

  • are intended for Alice.

  • However, the attacker cannot decrypt messages that where sent by Alice because that requires

  • Bob's private key.

  • Asymmetric encryption is used in a lot of places where security really matters.

  • You might not be aware of it, but everytime you visit a secure website via HTTPS, you're

  • actually using asymmetric encryption.

  • It's also being used to securily send emails with the PGP protocol.

  • And one last example: Bitcoin also uses asymmetric encryption to make sure that only the owner

  • of a money wallet can withdraw or transfer money from it.

  • So now you know how asymmetric encryption works and what the differences are between

  • asymmetric and symetric encryption.

  • If you liked this video, consider supporting me by sharing it and subscribing to my YouTube

  • channel and as always: thank you very much for watching!

Encryption is the process of taking a message and scrambling it's contents so that only


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B2 中上級

非対称暗号化 - 簡単に説明 (Asymmetric encryption - Simply explained)

  • 62 3
    Yi-Cheng Guo に公開 2021 年 01 月 14 日