An identity authentication encrypted by the sender's private key

Identity certification issued by CA organization

Public key infrastructure is a collection of hardware, software, personnel, policies and procedures used to realize the generation, management, storage, distribution and revocation of keys and certificates based on public key cryptography.

Keyed hash

The specific process of using MAC to verify message integrity is: assuming that the communicating parties A and B share the key K, A uses the message authentication code algorithm to calculate the message authentication code Mac from K and the message M, and then sends Mac and M to B together. After receiving Mac and M, B uses M and K to calculate the new verification code Mac*. If Mac* and Mac are equal, the verification is successful, proving that the message has not been tampered with. Since the attacker does not have the key K, the attacker cannot calculate the corresponding message verification code after modifying the message content, so B can discover that the message integrity has been destroyed.

factoring prime numbers

subtopic

A group of 3 bytes, then converted to 4 bytes, and then find the corresponding encoding from the base64 encoding table

Attachments when sending emails, SMTP protocol of emails: encode pictures and binary files, and then use base64 to decode after the other party receives them.

There cannot be special characters in the header of an http request, otherwise it cannot be parsed. So when you encounter special characters, you need to base64 encode them so that the browser can parse them.

Used in pictures. src is a base64 encoding. It can run anywhere without any dependencies.

Purpose of birth: to put all the characters in the world together

Requires large storage space

Use 32 bits, or 4 bytes, to represent a character, which basically covers all characters in the world.

Encryption and decryption with the same key

Data encryption standard, the IBM solution selected by the US National Secret Service, the key length is 56 bits, and the total number of keys is 2^56, which may be exhaustively cracked

ECB

CBC

DES upgraded version, in order to cope with the rapid development of computer capabilities, can brute force crack 56-bit length DES within 24 hours. 3DES uses 3 times DES. If the keys are different 3 times, the key will reach 168 bits, which greatly extends the time of brute force cracking. time

Advanced Encryption Standard, the standard selected by the U.S. Office of Secrets for the next generation of encryption algorithms.

You can use 128, 192, and 256-bit keys and use 128-bit block encryption to decrypt data, which is faster and more secure than 3DES.

RC2

RC4

RC5

2017

Encryption and decryption use different keys, public key encryption, private key decryption, private key decryption, public key encryption

The "private key" is processed by the SECP256K1 algorithm to generate the "public key". SECP256K1 is an elliptic curve algorithm. When a "private key" is known, the "public key" can be calculated. However, when the "public key" is known, the "private key" cannot be calculated in reverse.

Digital signature and encryption algorithms can be used, but as the key length increases, the performance drops sharply.

Based on a very simple fact of number theory: it is easy to multiply two large prime numbers but very difficult to factor them, so the product can be made public as an encryption key

2048 bits

Can only be used for digital signatures and cannot be used for encryption

The advantage of ECC compared to other asymmetric encryption algorithms is that its key is smaller. Although RSA has a high security level, its shortcomings are also obvious, that is, encryption and decryption take a long time.

Elliptical encryption algorithm 256 bit

Convert target text or file into an irreversible digest string of the same length

SHA and MD5 are actually similar. They are just different hash functions, the number of magic segments and iteration methods, the number of iterations, and the final digest length.

crack

128 bits 16 bytes

160 bits 20 bytes

SHA224

SHA256

SHA384

SHA512

java9 starts to support

faster than sha2

Because the hash algorithm is to group and combine the original text according to the specified number of digits. There are many ways to combine this, so it cannot be reversed. The hash collision probability SHA-n, then its security level is: 2^(n/2)

Several commonly used hashing algorithms group plaintext according to a certain length (such as 512 bits). If the length of the last group is not enough for a specific value (such as 448 bits), the bits are padded to make the length a specific value, and then the next group is added. The length of the actual information contained in the plaintext is recorded in a certain space (such as 64 bits). Then each group is calculated in order from front to back, and the calculation results of the current group are involved in the calculation of the next group until the last group of calculations is completed. The result obtained in this way is the final hash value. It is precisely this method that makes hash calculations, no matter how long the input is, the output is fixed length.

Because the hash algorithm is to group and combine the original text according to the specified number of digits. There are many ways to combine this, so it cannot be reversed.

Our country has also formulated its own symmetric encryption algorithm, called the national encryption algorithm. SM1 is equivalent to AES and SM2 is equivalent to ECC.

Symmetric encryption

asymmetric encryption

Data is encrypted and decrypted using symmetric encryption algorithm, which is fast and compact

Determine the identity of the data sender and non-repudiation through digital signatures

The hash algorithm ensures that the data has not been tampered with during transmission.

Symmetric encryption encrypts large files, asymmetric encryption encrypts keys

It is a protocol designed by the IETF based on SSL 3.0. It is an upgraded version of the SSL protocol. The difference between the two is very small, it can be understood that TLS is SSL 3.1