Electronic cash is actually a technology to simulate cash in electronic form. E-cash system attempts to copy the characteristics of cash for online transactions in many aspects: convenience, low cost (or no transaction cost). Anonymity and other attributes. However, not all electronic cash systems meet these characteristics, and most electronic cash systems can provide convenience for small online transactions.

The full name of electronic cash: electronic cash. Also known as electronic money or digital currency (di

Electronic cash flow

Gital cash is a very important electronic payment system, which can be regarded as the electronic or digital simulation of real money. Electronic cash exists in the form of digital information and circulates through the Internet. But it is more convenient and economical than real money. Its simplest form includes three subjects: merchants, users and banks; And four security protocol processes: initialization protocol, withdrawal protocol, payment protocol and deposit protocol. Chaum [2] put forward the first electronic cash scheme in 1982. It is implemented by blind signature technology, which can completely protect the privacy of users. However, this completely anonymous electronic cash has also provided convenience for many criminals, who use its completely anonymity to carry out some illegal and criminal activities, such as corruption and illegal purchases (such as buying drugs and arms). ), extortion and so on. Even if the police get the stolen money, they can't catch the criminal. Therefore, a reasonable electronic cash system should be incomplete or conditionally anonymous. In 1995, Stadhle et al [3] put forward the concept of fair blind signature, which can be used in conditional anonymous payment system. In 1996, Camenisch et al. [4] and Frankel et al. [5] independently put forward the concept of fair off-line electronic cash for the first time, and gave two schemes at the same time. The anonymity of users in fair electronic cash is incomplete, and it can be revoked by a trusted third party (TTP), thus using the complete anonymity of electronic cash to prevent criminal activities.

Electronic cash is a mature electronic payment method, which is suitable for small transactions paid through the network.

Characteristics of electronic cash:

1. There should be an agreement and authorization relationship between banks and merchants.

2. Users, merchants and electronic cash banks all need to use electronic cash software.

3. Electronic cash bank is responsible for the transfer of funds between users and merchants.

4. Electronic cash is anonymous to users, and the use of electronic cash can protect users' information.

Electronic cash plays the same role as ordinary cash in the economic field, which is very important for normal economic operation.

This is crucial. Electronic cash should have the following characteristics:

1. Independence: The security of electronic cash cannot be guaranteed by physical security alone, but by various cryptographic technologies used by electronic cash itself;

2. Non-repetitive expenses: Electronic cash can only be used once, and repetitive expenses can be easily detected;

3. Anonymity: Banks and merchants collude with each other, so it is impossible to track the use of electronic cash, that is, it is impossible to link the purchase behavior of electronic cash users, thus hiding the purchase history of electronic cash users;

4. unforgeability: users can't make counterfeit money, including two situations: first, users can't make effective electronic cash out of thin air; Second, after users withdraw n effective electronic cash from the bank, they can't make effective electronic cash according to the withdrawal and payment information of these n electronic cash;

5. Transitivity: users can transfer electronic cash between users at will like ordinary cash and cannot be tracked;

6. Separability: Electronic cash can not only be used as a whole, but also be divided into smaller parts for multiple use. As long as the sum of the denominations of each part is equal to the original electronic cash, any amount can be paid;

The security and reliability of electronic cash are mainly realized by cryptographic technology, which mainly includes:

Segmentation and selection technology

1. Segmentation and selection technology: When users withdraw electronic cash, banks cannot know the identity information of users in electronic cash, but banks need to know that the extracted electronic cash is correctly constructed. The segmented selection technology is that the user correctly constructs n electronic cash and sends it to the bank, and the bank randomly selects N- 1 of them to give the user their structures. If the structure is correct, the bank thinks that the other structure is also correct and signs it.

Zero knowledge proof

2. Zero-knowledge proof: the prover proves to the verifier and makes him believe that he knows or owns a certain message, but the proof process cannot reveal any information about the verified message to the verifier. The above two technologies are used to embed the user's identity information into electronic cash.

certificate

3. Authentication: On the one hand, authentication is to identify that the sender of information in communication is true rather than false; On the other hand, it is to verify that the transmitted information is correct and complete and has not been tampered with, replayed or delayed.

Blind digital signature

4. Blind digital signature: the signing applicant sends the message to be signed to the signer after "blind transformation", and the signer does not know the specific content of the signed message. This technology is used to realize the anonymity of users.