Application and development of blockchain technology , Digital encryption is the key . Once the encryption method is cracked , The data security of blockchain will be challenged , The non tamperability of blockchain will no longer exist . Encryption algorithm is divided into symmetric encryption algorithm and asymmetric encryption algorithm , Asymmetric encryption algorithm is mainly used in blockchain , In asymmetric encryption algorithms, public key cryptosystems are generally divided into three categories according to the problems they are based on ： Large integer decomposition problem class 、 Discrete logarithm problems 、 Elliptic curve class .. This paper is written by qkljys123 Organize and release .

**The hash algorithm**

Hash, The general translation is hash 、 Hash , Or transliterate to hash , It's an arbitrary length Input （ It's also called pre mapping pre-image） Transform to fixed length by hash algorithm Output , The output is the hash value . This conversion is a kind of Compress mapping , That is to say , The space for hash values is usually much smaller than the space for input , Different inputs may be hashed into the same output , So it's impossible to determine the unique input value from the hash value . In short, it is a method of compressing messages of any length to a fixed length A summary of the news Function of .

**Key cryptography**- Until modern times , Cryptography is almost exclusively about encryption algorithm ： General information （ Plaintext ） Convert to incomprehensible data （ Ciphertext ） The process of ; Deciphering the algorithm is the opposite process ： From ciphertext to plaintext ; Cipher machine （cipher or cypher） Including these two algorithms , In general, encryption refers to encryption and decryption Technology . The specific operation of the cipher machine is determined by two parts ： One is the algorithm , The other is the key . The key is a secret parameter used in cipher algorithm , Usually only the correspondent has . In the history of , The key is usually used directly on the cipher machine without authentication or integrity test , The key comes from Cryptography field .

**3 Merkle Tree**

**3 Merkle Tree**

**4 digital signature **

**4 digital signature**digital signature （ also called Public key digital signature ） Only the sender of information can produce a digital string that others can't forge , This digital string is also an effective proof of the authenticity of the information sent by the sender . It's kind of like a normal physical signature written on paper , But it did Public key encryption Domain technology , Methods used to identify digital information . A set of digital signatures usually defines two complementary operations , One for signing , Another for verification . Digital signatures are asymmetric Key encryption technology And Digital summary Application of Technology .

**5 Proof of zero knowledge **

**5 Proof of zero knowledge**Proof of zero knowledge (Zero—Knowledge Proof), By S.Goldwasser、S.Micali And C.Rackoff stay 20 century 80 Put forward in the early s . It means that the certifier can provide the verifier with no useful information , To convince the verifier of the correctness of an assertion . Zero knowledge proof is essentially an agreement involving two or more parties , A series of steps that two or more parties need to take to complete a task . The prover proves to the verifier and makes him believe that he knows or has some information , But the proof process can't disclose any information about the verified message to the verifier . A lot of facts prove that , Zero knowledge proof is very useful in cryptography . If zero knowledge proof can be used for verification , Will be able to effectively solve many problems .

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** summary ****：**

To make a long story short , Blockchain technology as an emerging technology , It makes great use of the existing achievements of modern cryptography , Include hash 、 encryption 、 Digital signature, etc . On the other hand , Blockchain system and many new scenarios also put forward many new requirements for cryptography and security technology , In turn, it will promote the further development of related disciplines . Only on the basis of data security , Only blockchain can be promoted , So cryptography is the primary core of blockchain .