Cryptography can be a difficult subject to understand. It is full of mathematical proofs. Unless you really need to develop a cryptographic system, if you only want to understand cryptography from a macro perspective, you don't need to understand these complex contents.
If you open this article with the expectation of being able to create the next HTTPS protocol, I have to regret to say that only carrier pigeons are not enough. Otherwise, make some coffee and enjoy this article.
Alice, Bob and the carrier pigeon?
Any activity you do on the Internet (read this article, buy things on Amazon, upload pictures of cats) boils down to sending messages to the server and receiving messages from the server.
This may sound a bit abstract, so we might as well assume that this information is transmitted through carrier pigeons. I understand that this assumption is arbitrary, but trust me: HTTPS works like this, but it's much faster.
In this article, we will not use terms such as server, client and hacker. Instead, we will use the names of Alice, Bob, and Mallory in turn to replace them. If you are not trying to understand password concepts for the first time, you can recognize these names because they are widely used in technical literature.
A simple communication
If Alice wants to send a message to Bob, she will tie the message to the leg of the carrier pigeon and let the carrier pigeon pass it on to Bob. Bob receives the information and reads the information. everything is normal.
But what if Mallory intercepted Alice's carrier and changed the content of the message? Bob has no way of knowing that the information sent by Alice has been modified in transit.
This is how HTTP works. It's scary, right? I will not send my bank credentials via the HTTP protocol, and neither should you.
A secret order
What if Alice and Bob are both clever. They agreed to use secret orders to write information. They offset each letter in the alphabet by 3 positions. For example: D -> A, E -> B, F -> C. The plain text "secret message" will be converted to "pbzobq jbppxdb".
Now, if Mallory intercepts the carrier pigeon, she can neither change the information into some meaningful information, nor can she understand the content of the message, because she does not know the secret order. But Bob can simply reversely apply secret codes (A -> D, B -> E, C -> F) to decrypt the information. The ciphertext "pbzobq jbppxdb" will be decrypted back to "secret message".
That's it!
This is called symmetric key cryptography, because when you know how to encrypt a message, you also know how to decrypt the message.
The secret code I introduced above is often referred to as the Caesar cipher. In real life, we use more advanced and complex secret orders, but the main idea is the same.
How do we decide what the key is?
If only the sender and receiver know the key, symmetric key cryptography is very secure. In the Caesar cipher, the key is an offset value, which determines how much each letter should be offset. In our example, the offset value we used is 3, but it can also be 4 or 12.
But there is a problem with this design: before using pigeons to transmit information, if Alice and Bob have never seen it before, they have no secure way to create a key. If they include the key in the message, Mallory will intercept the message and discover the key. The consequence is: No matter whether the information sent by Alice and Bob is encrypted or not, Mallory can read or change the intercepted information.
This is a typical example of a man-in-the-middle attack. The only way to avoid it is to change the previous password system.
Homing pigeon carrying a box
So Alice and Bob came up with a better system. When Bob wants to send a message to Alice, Alice will follow the following process:
Bob sends a carrier pigeon to Alice, which does not carry any information.
Alice passes the pigeon back to Bob, who carries an open box and key.
Bob puts the information in the box, locks the lock, and sends the box to Alice.
Alice receives the box and uses the key to open the box and read the information.
In this way, it is impossible for Mallory to change the information by intercepting the pigeon, because she does not have the key. When Alice wants to send a message to Bob, follow the same process.
Alice and Bob just used what is commonly known as asymmetric key cryptography. It is called asymmetric because even if you can encrypt a message (lock the box), you cannot decrypt it (open the locked box).
How can I trust this box?
If you are careful enough, you may have realized that we still have a problem. When Bob receives the open box, how can he be sure that this is from Alice's box, and not Mallory. After intercepting the pigeon, he replaces the box from Alice with the box that Mallory sets the key.
Alice decides to digitally sign the box. In this way, when Bob receives the box, he checks the consistency of the signature to determine whether the box comes from Alice.
Some people may wonder how Bob recognizes Alice's signature? Good question. Alice and Bob have the same question. So they decided to have Ted digitally sign the box instead of Alice.
Who is Ted? Ted is a famous and trustworthy person. Everyone can get a signature from Ted, and everyone believes that Ted will only provide the digital signature service of the box to legitimate people.
Only when Ted is sure that the person requesting the signature is Alice, Ted will provide Alice with the box digital signature service. Therefore, Mallory can no longer intercept Alice's box, replace the box and send it to Bob as before, because Bob will find that this box is digitally signed at Ted by Mallory, not Alice.
Ted is usually referred to as a certificate authority in technical terms, and the browser you use to read this article has the signatures of various certificate authorities installed.
So when you connect to a website for the first time, you trust its box because you trust Ted, and Ted tells you that the box is legal.
The box is too heavy
Alice and Bob now have a reliable communication system, but they realize that the pigeon carrying the box is too slow compared to the pigeon carrying the information.
They decided to only use the box method (asymmetric cryptography) when passing the key, and use symmetric cryptography to encrypt the information (remember the Caesar cipher mentioned earlier?).
In this case, it can be described as the best of both worlds: the reliability of asymmetric cryptography and the efficiency of symmetric cryptography are both.
In the real world, the transmission speed of the "carrier pigeon" is very fast, but despite that, the use of asymmetric cryptography to encrypt messages is slower than the use of symmetric cryptography, so we only use it to exchange encryption keys.
Now that you know how HTTPS works, your coffee should be ready. Go drink it, you deserve it.
The Multiple Power Selection Column Loudspeaker Series which produce good clear sound and acoustical clarity for background music and paging,are suitable for indoor and outdoor applications such as stations, gardens, swimming pools,stadiums, and tennis courts, etc.
Even in extreme weather conditions, the all metal extruded aluminum alloy enclosure with cast aluminium top and bottom plates are fully dust and weatherproof
Column Speaker,Column Speakers,Sound Column, Column Loudspeaker, Aluminium Alloy Outdoor Column Speaker
Taixing Minsheng Electronic Co.,Ltd. , https://www.ms-speakers.com