# Proxy Signature-Based Management Model of Sharing Energy Storage in Blockchain Environment
## 3 Blockchains and Authentication Technology
### Digital Signature on Blockchains  
On a blockchain, the off-line participants of SES are mapped as the nodes. Therefore, the operations of a node, such as information issuing, bidding, data querying and contract signing, have the same legal effect as that of the corresponding off-line participant in the market. In this case, it is crucial for a node to obtain the reliable on-line encrypted identity and authenticate the identity of the information received from other nodes. A digital signature is an important technology to identify information in the digital age and it is also applied in blockchains.  
The basis of a digital signature is digital digest and asymmetric encryption. A message is transferred into a fixed length message digest by digital digest technology, and asymmetric encryption technology is used to encrypt the message digest. In fact, the digital digest technology is hash functions, transferring the information of any length into a fixed length message digest which is hard to restore to the original information. Due to the very low collision probability, it can be considered that the two pieces of original information should be the same if their message digests are the same. This feature can be used to compare the consistency of information. Therefore, information tampering is effectively prevented and the security is ensured.  
Asymmetric encryption, also known as a two-key system, consists of a pair of keys--i.e., a public key and private key. A node has a private key firstly, and then a public key is generated by a function and the private key. The public key also includes the information of random variables except for the private key. Therefore, the private key cannot be obtained by cracking a public key though the public key is public to all. On the other hand, a pair of complementary algorithms is defined in the digital signature--i.e., encryption algorithm for the signature and decryption algorithm for verification. When one of the public or private keys is used to sign for the message digest by the encryption algorithm, the other one is used to verify the signed message by the decryption algorithm. In the process, the message that is not signed by the target node cannot be validated by the received node, and the integrity and reliability of the message can be confirmed.  
According to the aforementioned principles, the basic characteristics of digital signatures are obtained easily. Firstly, the message cannot be modified after it has been signed. Secondly, all nodes receiving the message can confirm the signer's identity according to the digital signature because of the uniqueness and complementarity of the key pair. Thirdly, the signer cannot deny the message signed by him--i.e., the signature is undeniable. Finally, it is difficult for anyone else to forge the digital signature of the legal signer. In conclusion, digital signatures can replace the traditional handwritten signature and be sealed in the blockchain environment, representing recognition with a legal effect for messages. The key pair is the identity of nodes on blockchains.