Implementation of cryptographic algorithms on Java use case notes

1th Chapter Basic Knowledge

1.1. One-Key cipher system

Single-key cryptosystem is a traditional encryption algorithm, which means that the sender and receiver of the information together use the same key to decrypt.

In general, the encryption algorithm used is relatively simple and efficient, key short, encryption and decryption speed, deciphering extremely difficult. But the security of encryption relies on the security of key custody, it is a serious problem to transmit and keep the key securely on the open computer network, and if the security of the key is also a problem in the case of multi-user.

The single-key cryptosystem is represented by the United States des

1.2. Message Digest

A message digest is a digital fingerprint of a block of data. That is, a data block of any length is computed to produce a unique fingerprint (for SHA1 is to produce a binary array of 20 bytes).

The message digest has two basic properties:

Two different messages are difficult to generate the same summary

It is difficult to generate a message for the specified digest, and the specified summary is inferred from the message

Representative: SHA1 of the American Institute of National Standards and technology and Ronald Rivest of MIT MD5

1.3. Diffie-hellman Key Agreement

The key agreement is an idea proposed by the founder of Diffie and Hellman of public key cryptography.

Prerequisites, allowing two users to exchange information on the public media to generate a "consistent", sharable key

Representative: Exponential key agreement (exponential key agreement Protocol)

1.4. Asymmetric algorithms and public key systems

In the 1976, Dittie and Hellman to solve key management problems, in their groundbreaking work "new Direction of cryptography", a key exchange protocol, which allows the exchange of information between the two sides of the communication in the insecure media, securely transmits secret keys. On the basis of this new idea, the asymmetric key cryptosystem, that is, public key cryptosystem, is quickly appearing. In the public key system, the encryption key is different from the decryption key, and the encryption key is publicly available to anyone, and the decryption key is only known to the decrypted person. They are known as public keys and secret keys (private key), respectively.

The RSA system is one of the most famous and most used in all public key cryptography systems to date. The RSA public key cryptography system was proposed by Professor R.rivest, A.shamir and L.adleman in 1977. RSA's name is the first letter from the surname of the three inventors.