What is Public Key Theory? Principles of public and private keys

To understand a public key, you must first understand the key. , a key is defined as a parameter, which is the data that is entered in an algorithm that converts plaintext to ciphertext or ciphertext to plaintext. There are two types of keys, one is the public key and the other is the private key.

The private key is a piece of decrypted data that you keep for yourself, while the public key is open to the public. The public key and the private key are a key pair obtained through an algorithm, and the public key must be used to decrypt the data encrypted with the private key, and if the private key is encrypted, it must also be decrypted with the public key. As for the rest.

It seems that there are many, so I won't go into details. After all, key theory is the foundation of the whole of cryptography. If you want to explain it all in detail, you can write a book.

A public key is the exposed part of a key pair, and it is typically used to encrypt a session key, verify a digital signature, or encrypt data that can be decrypted with a corresponding private key.

A key is a key that the owner of the key should hide on the public key cryptographic infrastructure. In a public-key cryptography, the public key and the key are paired, and we assume that when the public key is released to a third party, the private key should be kept secret.

Before the advent of public-key cryptography, public-key cryptography was commonly used because the encryption key and the decryption key were the same and were shared with a communication partner to encrypt the communication. However, if it is eavesdropped during the exchange of keys, public key encryption has no cryptographic significance.

With public-key cryptography, the owner of the key first passes the public key to the communication partner. The communication partner uses the public key to encrypt and sends the encrypted document (data) to the owner of the key, and the owner of the key to receive the encrypted document decrypts the document with the private key, and the key required to decrypt the document is not exchanged on the communication path, making it easier to ensure security.

The most widely used public-key encryption is RSA encryption, in which the public key and the key have the same structure, and the key encrypted with one key can be decrypted with the other, in other words, it can be used not only to encrypt with the public key, decrypt with the key, but also to encrypt with the key and decrypt with the public key.

Digital signatures use this feature in such a way that it is not possible to create an encrypted document that can be decrypted with a specific public key so that the owner of the key can be guaranteed unless it is the person who has the key paired with the public key.

However, it should be noted that the private and public keys of RSA are never symmetrical. It is possible to create a public key from a private key, but it is considered very difficult and impossible to create a key from a public key, and the security of RSA is based on the fact that it is difficult to break down a large number of factors, so it is necessary to extend the key length for better security.

Since new decoding algorithms are expected to be discovered in the future and computational speeds will increase, key lengths and algorithms will also change.

1) Bob has two keys, one is the public key and the other is the private key.

2) Bob gives the public key to his friends--- Patty, Doug, Susan, --- one each.

4) After Bob received the letter, he decrypted it with his private key and saw the contents of the letter. The emphasis here is that as long as Bob's private key is not revealed, the letter is safe and cannot be decrypted even if it falls into someone else's hands.

9) Susan then uses the hash function on the letter itself to compare the results obtained with the summary obtained in the previous step. If the two are consistent, it proves that the letter has not been modified.

The HTTP protocol is easy to be tampered with and hijacked, such as some unscrupulous operators will implant ads in your page through the server.

Therefore, many ** choose to use the https protocol. The HTTPS protocol provides three major functions: content encryption, identity authentication, and data integrity through the TLS layer and certificate mechanism.

1) Below, let's look at an app"Digital certificates"Example: https protocol. This protocol is mainly used for web encryption.

2) First, the client makes an encryption request to the server.

4) Client's (browser)."Certificate Manager", there is"Trusted Root Certification Authority"List. Based on this list, the client checks to see if the public key of the unlocked digital certificate is in the list.

The theoretical basis of public key cryptography is based on mathematical principles, which can provide greater security and reliability.

The study of the objective law of cryptographic changes and the application of the compilation of ciphers to keep communication secrets is called coding; It is applied to deciphering codes to obtain communication information, which is called decipherment, and is generally referred to as cryptography. The telegraph was first invented by Morse in the United States in 1844, so it is also called Morse code. It consists of two basic signals and different intervals, short dot signals.

Cryptography is the technical science that studies the compilation of ciphers and the decipherment of ciphers. To study the objective law of password change, and apply it to the compilation of ciphers to keep communication secrets, call hail orange coding; The application of code-breaking to obtain communication intelligence is called decipherment. Cryptography in general.

Cryptography (in Western European languages, derived from the Greek kryptós "hidden", and gráphein "written") is the study of how information is conveyed in secret. In modern times, it refers specifically to the mathematical study of information and its transmission, and is often considered a branch of mathematics and computer science, and is also closely related to information theory.

The famous cryptographer Ron Rivest explains: "Cryptography is about how to communicate in an environment where the enemy exists", which is equivalent to the similarities and differences between cryptography and pure mathematics from an engineering point of view. Cryptography is the core of information security and other related topics, such as authentication and access control.

The primary purpose of cryptography is to hide the meaning of information, not to hide the existence of information.

Public-key cryptography algorithms.

The keys in public key cryptography algorithms can be divided into two types: public key and private key according to their nature.

A user or system generates a pair of keys, and one of them is made public, called a public key; The other is kept by itself and is called the private key.

Anyone who learns the user's public key can use the user's public key to encrypt the information and interact with the user securely.

Due to the dependency that exists between the public key and the private key, only the user themselves can decrypt the information, and no unauthorized user or even the sender of the message can decrypt this information.

In the research of modern public-key cryptography, its security is based on intractable computable problems.

For example: (1) large number decomposition problem;

2) compute the discrete logarithm problem of finite domains;

3) the square remainder problem;

4) The logarithm problem of elliptic curves, etc. Based on these problems, various public-key cryptography systems have emerged.

There are many studies on public key cryptography, mainly focusing on the following aspects:

1) Research on the RSA public key system;

2) the study of elliptic curve cryptography;

3) Research on various public-key cryptography;

4) Digital signature research.

Public-key cryptography has the following advantages:

1) Simple key distribution;

2) The amount of key saved is small;

3) It can meet the confidentiality requirements of private conversations between people who do not know each other;

4) Digital signature and digital authentication can be completed.

The answer is supplemented. SHA-1 algorithm.

The SHA-1 hash algorithm [4] was originally designed for the DSA algorithm, and its design principle is similar to that of the MD2, MD4, and especially MD5 hash functions proposed by Ron Rivest. When a message with a length of < 264 bits is input, a 160-bit digest is output, and the algorithm is divided into 5 steps:

1) Fill the message to make its length a multiple of 512 minus 64, the method of filling is to add a "1" after the message, and then add "0" until the required length is reached, requiring at least 1 bit, up to 512 bits to fill the bits;

2) After completing step 1, append the message length value before 64bit filling to the newly obtained message;

3) Initialize the cache, SHA-1 uses a 5-word cache, each word is 32 bits;

4) Enter the main loop of message processing, one loop processes 512bit, the main loop has 4 rounds, each round of 20 operations;

5) At the end of the cycle, the resulting output value is the desired value.

1.The public key and the private key are two files that have been algorithmically obtained, and a private key corresponds to only one public key, that is, it is unique.

The path of the key: *PKR is the public key and *SKR is the private key.

PGP is generally used to send a lot of emails, and has been supported by out look or third-party email clients. When sending an email, PGP will detect that there is a session (the encryption method can be set in the PGP software: all emails, specified domain names or recipients, etc.), and it will automatically query the local public key and send it out encrypted.

If you want to send only one file, you can use the "New PGP Archive" in the PGP software to encrypt it, set a separate password, or use the other party's public key to encrypt it.

On the left side of the software interface: the public key is generally in the "All Keys", and the personal private key is in the "My Private Key". If you want to give the public key to someone else, you can export it on the public key>.

(It's a *.)asc). In the menu "Keys" there is the PGP keyring attribute.

You'll see where the public and private keys are kept.

4.If the email is set, PGP will be automatically encrypted and decrypted. When sending the file, encrypt it in "New PGP Archive", the last sentence of point 2 on the week.

The private key will not be in someone else's possession, only in your own hands. Unless you send it to the other party, encrypt the file with the other party's public key, and then the other party uses their private key to decrypt the file encrypted with their own public key, and vice versa, the other party uses your public key to encrypt and send it to you.

What is generated is a pair of public and private keys that are two files, as in point 1 above. When the email is encrypted, the software automatically helps you encrypt it with the other party's public key, which you usually don't have to worry about. When encrypting files, pay attention to who they are sent to and encrypt with whose public key, because they are unique.

Follow-up question: The verified option in is gray, not a green checkmark, please ask if there is an impact, and if so, how to correct it.

Answer: Sending an email will definitely have an impact, the PGP software will not be enabled in gray, and sending an email will prompt that the public key cannot be found, and you need to manually sign the name, and right-click the gray public key "sign" to sign. This situation is usually due to the fact that the other party did not verify it after uploading it on the PGP server or a bug in the PGP software

2.The public key sent to the server is linked to the mailbox, so you can directly attack the mailbox, remake the public key, and send the public key to the server to replace the original public key, so that you can impersonate the original public key and decrypt it with the new private key. It's not safe.

Answer: A private key corresponds to only one public key, that is, it is unique. Don't forget that the private key is only in your own hands.