sequence

As a noob, symmetric encryption, asymmetric encryption, digital signature, digital certificate, CA, diff-helman, DES, AED, RSA... none of these will. Therefore, Baidu starts, and first understands it initially.

practical application

I'm a novice... 0 basics, so let's do some practical applications, this is easier to understand than mathematical formulas.

page 1

How does the Enigma cipher machine work? _哔哩哔哩_bilibili

This is a 3D modeling animation.

From here, it can be found that it is symmetrical, if Y->E, then there is also E->Y. Because, with the same wire, if the current flows in from one end, it will definitely flow out from that end, and if it flows in from that end, it will definitely flow out from this end.

page 2

[Homemade Chinese characters] Demonstration and cracking of the principle of the German Enigma cipher machine in World War II

Encrypted demo:

[[Homemade Chinese characters] Demonstration and cracking of the principle of the German Enigma cipher machine in World War II] [Precise airborne to 01:07]

Decrypted demo:

[[Homemade Chinese characters] Demonstration and cracking of the principle of the German Enigma cipher machine in World War II] [Precise airborne to 05:30]

Almost, just upside down.

page 3

It's not a video, it's a long text

How did Alan Turing decipher Ingmar in The Imitation Game? - Answer at 11:30 - Zhihu

A cryptomonster created by a machine that only a machine can defeat.

Initial understanding, Baidu

[Live Playback] Translator Sharing of "Graphic Cryptography Technology": Interesting & Useful Cryptography_哔哩哔哩_bilibili

Following this video, let's take a look at these concepts on Baidu. Ignore the details for now, and just know the general idea here.

passwords in history

seen above...

modern cipher

Existing problems and solutions

Symmetric encryption

At least, you know, the key, is a string of numbers

Principle of Symmetric Encryption - An Ancient Encryption Method_哔哩哔哩_bilibili

Concrete and XOR-related

used reflexive

The reflexiveness of XOR, here is the flipping of chess pieces, which is very vividly explained

asymmetric encryption

The key is also a number

This flow chart is pretty good

Power refers to this, this flow chart is also very vivid

The comments at the bottom of this video are quite vivid... probably a little bit.

Understand asymmetric encryption in four minutes_哔哩哔哩_bilibili

This is a more specific flowchart

On the Internet, how to transmit information confidentially. The principle of RSA encryption algorithm that elementary school students understand._哔哩哔哩_bilibili

Because the modular operation is not very reversible, it cannot be reversed; then, can you guess the key and do it right?

Algorithm that can be understood even if you are not good at mathematics - RSA encryption and decryption principle and process_哔哩哔哩_bilibili

D is related to E,T

E is known in the public key, so only T is required

T is related to p, q, and N=pq, N is known in the public key, so it is enough to deduce pq from N, how to do it - just factorize N. But this calculation is not small, and it is not a big deal, so it is not good to do it right away.

To sum up, it doesn't work if you do it backwards or in the opposite direction.

Also, that pq seems to be randomly generated

Hashing and Integrity

Practical examples:

some features

One-way: think of it as a lossy compression, long becomes short! so there is no way to restore

The drawer principle, 7 drawers and 8 balls, must be repeated. Good hashes don't have this problem.

Application: no need to store passwords in plain text

The random number [salt] is added to prevent dictionary attacks, that is, to calculate in advance and wait there. For example, calculate the commonly used password 123456 in advance, and wait for the rabbit.

message authentication code

To prevent the message from being tampered with by a third party in the middle, it is similar to the one above adding salt and then hashing

But there is still a problem: the middleman records and replays it multiple times...

digital signature

equivalent to signature

The public key is encrypted and the private key is decrypted in reverse.

Is there a comparison process? Both the message and the digital signature have been sent.

There is another problem: the message is too long, and the digital signature [ciphertext] is also very long, which is not easy to transmit.

Therefore, there is such a thing as calculating the digest of the message hash value first, and signing the digest. After the signed digest is decrypted, the digest is obtained, and then the message is hashed again, and if it matches, it will be fine.

this is more specific

Principles of digital signature and digital certificate_哔哩哔哩_bilibili

It will be easier to understand if you read it in pairs with the handwritten signature. Sign to prevent non-acceptance?

It can be used to prevent the downloaded app from being tampered with and implanting other things

But there are also problems. Anything related to the public key and private key will have the problem of man-in-the-middle attack. Digital signatures are the reverse of public and private keys, so they also exist.

Middleman, invisible person; often encountered, because the Internet will go through many proxy servers

what to do? How do I know this public key belongs to bob and not the middleman? Find an organization to certify - digital certificate

digital certificate

Will trent be intercepted by a middleman? Make a trent of trent, doll...

In the end, a root certification authority was set up, not many, not many.

Feasible roots, RCA, not many, so all are pre-buried in the operating system. With this public key, you can verify it layer by layer to see if it is reliable.

Therefore, don't install any magically modified or pirated operating systems.

A more specific flowchart:

Principles of digital signature and digital certificate_哔哩哔哩_bilibili