Summary of symmetric and asymmetric and reversible non-reversible encryption algorithms

Remember before the test soft test and recent exams, always appear the problem of encryption algorithm, summed up here.

Summary of symmetric and asymmetric and reversible non-reversible cryptographic algorithms:

According to the different key types, modern cryptography can be divided into two types: symmetric encryption Algorithm (private key cryptosystem) and asymmetric encryption algorithm (public key cryptosystem).

1 symmetric encryption algorithm, data encryption and decryption are all the same key, so its security depends on the security of the held key.
The main advantage of symmetric encryption algorithm is that the encryption and decryption speed is fast, the encryption strength is high, and the algorithm is open.
The disadvantage is that the secret distribution of the key is difficult, in the case of a large number of users, the key management complex, and can not complete the identity authentication and other functions, not easy to apply in the network open environment.
The symmetric encryption algorithm is characterized by its openness, low computational capacity, fast encryption speed and high encryption efficiency.
At present, the most famous symmetric encryption algorithm has data Encryption Standard DES, but the traditional des because only 56-bit key, so it has not adapted to the current distributed open network of data encryption security requirements. European Data Encryption Standard idea and so on, currently the most encrypted symmetric encryption algorithm is the Advanced Encryption Standard AES,AES provides 128-bit key, 128-bit AES encryption strength is 56-bit DES encryption strength of 1021 times times more.

The symmetric encryption algorithm process is to send the data sender to the plaintext (raw data) and encryption key together after the special encryption algorithm processing, so that it becomes a complex encrypted ciphertext sent out. After receiving the ciphertext, if you want to interpret the original text, it is necessary to decrypt the ciphertext by using the encryption key and the inverse algorithm of the same algorithm, so that it can be restored to readable plaintext. In the symmetric encryption algorithm, only one key is used, both parties use this key to encrypt and decrypt the data, which requires the decryption party must know the encryption key beforehand.
The disadvantage is that both sides of the transaction use the same key, the security is not guaranteed. Assuming that two users need to encrypt and then exchange data using the symmetric encryption method, the user needs at least 2 keys and is exchanged, and if there are N users in the enterprise, the entire enterprise needs NX (n-1) keys.

2 Asymmetric Encryption algorithm
Asymmetric encryption algorithms use two pairs of keys that are completely different but perfectly matched (that is, a public key or encryption key and a private key or decryption key)-the public and private keys. When encrypting a file using an asymmetric encryption algorithm, the process of encrypting and decrypting the plaintext is accomplished only by using a matching pair of public and private keys. When encrypting plaintext, the public key is encrypted, the private key is used to decrypt the text, and the originator (the dongle) knows the public key of the receiving party, and only the recipient (the decryption) is the only one who knows its private key. The basic principle of asymmetric encryption algorithm is that if the originator wants to send encrypted information that only the receiving party can read, the originator must first know the receiver's public key and then use the public key of the receiving party to encrypt the original text; After the recipient receives the encryption, it uses its own private key to decrypt the text.
The widely used asymmetric encryption algorithm has the RSA algorithm and the United States National Standards Bureau proposed DSA.
The confidentiality of asymmetric encryption algorithm is good, it eliminates the need for end-users to Exchange keys, but encryption and decryption takes a long time, slow, it is not suitable for encrypting files and only applicable to a small amount of data encryption.

Symmetric encryption algorithm, asymmetric encryption algorithm and irreversible encryption algorithm can be applied to data encryption, identity authentication and data security transmission respectively.

3 non-reversible encryption algorithm

The non-reversible encryption algorithm is characterized by the encryption process does not need to use the key, the input plaintext after the system directly through the encryption algorithm processing into ciphertext, the encrypted data can not be decrypted, only re-enter the plaintext, and again through the same irreversible encryption algorithm processing, to obtain the same encryption ciphertext and the system re-recognition, To really decrypt it. Obviously, in this type of encryption process, encryption is itself, decryption is itself, and so-called decryption, is actually to re-add a secret, the application of the "password" is the input plaintext. Non-reversible encryption algorithm has no key storage and distribution problems, it is very suitable for distributed network systems, but because of the complexity of cryptographic computation, the workload is very heavy, usually only in the case of limited data volume, such as widely used in computer system password encryption, using the irreversible encryption algorithm. In recent years, with the continuous improvement of computer system performance, the application field of irreversible encryption is increasing gradually. In the computer network, there are many non-reversible encryption algorithms, the MD5 algorithm invented by RSA company and the non-reversible encryption Standard SHS (secure Hash Standard: Security clutter standards) proposed by the U.S. National Standards Bureau.

The more famous

1 symmetric DES (Data Encryption Standard), AES (Advanced encryption)

2 asymmetric SHS RSA (

The RSA public Key cryptography algorithm was introduced in 1977 by Ronald Leevist (Ron rivest), Adi Samor (Adi Shamir) and Lennard Adman (Leonard Adleman). At the time, all three of them worked at MIT. RSA is the first letter of their three surnames made together. RSA is currently the most influential public-key encryption algorithm, it can resist the most known password attacks so far, has been recommended by the ISO public key data Encryption standard. ）

3 Irreversible MD5

MD5,SHS encryption is a hash encryption algorithm

Summary of symmetric and asymmetric and reversible non-reversible encryption algorithms