Http and Https belong to the category of computer networks, but as a developer, it is necessary to master them in both background development and foreground development.

in the process of learning Http and Https, I mainly refer to teacher Ruan Yifeng's blog, which is comprehensive and easy to understand. Interested students can learn.

this article mainly explains the understanding of Http and Https according to my own ideas. The article will be introduced from the following aspects.

directory tree (I don't know how the editor jumps within the page through the directory tree for the time being, and any student knows that he wants to let me know):

As can be seen from the directory structure, each title is a big theme. However, the purpose of this paper is to let all students have a comprehensive understanding of Http and Https-related knowledge, and not to discuss various topics too deeply. Interested students can conduct targeted research.

there are two mainstream hierarchical modes of network structure: OSI seven-layer model and TCP/IP four-layer model.

OSI refers to Open System Interconnect, which means open system interconnection.

TCP/IP refers to the transmission control protocol/internet protocol, which is the most widely used protocol in the world.

Http is an application protocol based on TCP/IP protocol, which does not include the transmission of data packets. It mainly specifies the communication format between the client and the server, and uses port 8 by default.

Request format:

Response format:

explain some fields of the request header and the response header:

both http and Https protocols will establish Tcp connection through Tcp three-way handshake when requesting. So, what does three-way handshake mean?

So, why do we have to go to three-way handshake? Can we do it once? How about twice? With these questions, let's analyze why it must be three-way handshake.

Through three-way handshake, both A and B can confirm their ability to send and receive messages with each other, which is equivalent to establishing mutual trust and starting communication.

Next, let's introduce the specific content sent by three-way handshake, which is described as follows with a picture:

First, let's introduce some concepts:

After knowing the above concepts, let's take a look at the specific process of three-way handshake:

As can be seen from the figure, The connection has gone through three-way handshake. When the data transmission is completed, the connection needs to be disconnected, and the disconnection has gone through four waves:

The following is the format diagram of the Tcp segment header, which is very important for understanding the Tcp protocol:

Https protocol is an Http channel with security as the goal, which is simply a secure version of Http. It is mainly to add SSL layer (SLL/TLS is the mainstream now) under Http, and SSL is the security foundation of Https protocol. The default port number of Https is 443.

Http protocol was introduced earlier. Can you tell me the risks of Http?

SSL/TLS protocol is designed to solve these risks, hoping to achieve:

The following mainly introduces SSL/TLS protocol.

the basic idea of SSL/TLS protocol is to adopt public key encryption (the most famous is RSA encryption algorithm). The general process is that the client asks the server for the public key, then encrypts the information with the public key, and the server receives the ciphertext and decrypts it with its own private key.

in order to prevent the public key from being tampered with, put the public key in a digital certificate, and if the certificate is trusted, the public key is trusted. Public-key encryption requires a lot of calculation. In order to improve efficiency, both the server and the client generate a dialogue key to encrypt information, and the dialogue key is symmetric encryption, which is very fast. And the public key is used to keep the conversation secret.

The following figure shows the SSL encrypted transmission process:

Describe the process in the figure in detail:

As mentioned above, SSL certificates are required in the Https protocol.

SSL certificate is a binary file, which contains the authenticated website public key and some metadata, and needs to be purchased from the dealer.

there are many types of certificates. Classification by certification level:

EV certificate browser address bar style:

OV certificate browser address bar style:

DV certificate browser style:

Classification by coverage:

The higher the certification level and the wider the coverage, the more expensive the certificate is. There are also free certificates. In order to promote Https, the Electronic Outpost Foundation established Let's Encrypt to provide free certificates.

There are also many distributors of certificates, among which Trust Asia is well known.

encryption algorithms are divided into symmetric encryption, asymmetric encryption and Hash encryption.

Symmetric encryption algorithm has high encryption and decryption efficiency and high speed, and is suitable for encryption and decryption of large amount of data. Common heap encryption algorithms include DES, AES, RC5, Blowfish, and IDEA

. Asymmetric encryption algorithms are complex, slow in encryption and decryption, but high in security, and are generally used in combination with symmetric encryption (symmetric encryption of communication content, asymmetric encryption of symmetric key). Common asymmetric encryption algorithms are RSA, DH, DSA, ECC

Hash algorithm. The characteristic is that the input values are the same, and the same hash value is obtained through the hash function, but the input values are not the same. Common Hash encryption algorithms are MD5, SHA-1, SHA-X series < P > The following focuses on RSA algorithm and DH algorithm.

Https protocol uses RSA encryption algorithm, which can be said to be the most important encryption algorithm in the universe.

RSA algorithm uses some number theory knowledge, including coprime relation, Euler function and euler theorem. The encryption process is not specifically introduced here. If you are interested, you can refer to the RSA algorithm encryption process.

the security of RSA algorithm is based on the problem of large number decomposition. At present, the largest key cracked is 7+ bits, which means that the 124-bit key and the 248-bit key can be considered absolutely safe.

The main difficulty in the decomposition of large numbers lies in the computing power. If the computing power is qualitatively improved in the future, these keys may also be cracked.

DH is also an asymmetric encryption algorithm.

the security of DH algorithm is based on discrete logarithm problem.

The differences between Http and Https are as follows:

After three days' study and summary, I finally finished this article, which can help readers grasp the knowledge framework of HTTP and Https in general. The content of each topic is not discussed in depth. When readers have their own knowledge framework, they can deeply understand the content of each knowledge point by themselves.

here is a summary: a summary of computer network related knowledge.