The electronic cash from the Postal Savings Bank cannot be withdrawn.

Postal Savings Bank’s electronic cash regulations:

1. Independence: The security of electronic cash cannot be guaranteed by physical security alone, it must be used by the electronic cash itself Various cryptographic technologies are used to ensure the security of electronic cash;

2. No repeated spending: Electronic cash can only be used once, and repeated spending can be easily checked;

3 , Anonymity: Banks and merchants cannot track the use of electronic cash through interoperability, that is, they cannot link the purchasing behavior of electronic cash users together, thereby concealing the purchase history of electronic cash users;

4. Unforgeable Safety: Users cannot create counterfeit coins, including two situations: first, users cannot create valid electronic cash out of thin air; second, after users withdraw N valid electronic cash from the bank, they cannot withdraw and pay based on the information of these N electronic cash. Create effective electronic cash;

In other words, once the electronic cash is deposited, it cannot be returned to the original route and cannot be transferred to other accounts. Therefore, the electronic cash of the Postal Savings Bank cannot be withdrawn.

Extended information:

1. Electronic cash classification

1. Electronic cash systems can be divided into account-based electronic cash systems and account-based electronic cash systems according to their transaction carriers. Electronic cash system for vouchers;

2. According to whether merchants need to conduct online verification with the bank when electronic cash is spent, it is divided into online electronic cash system and offline electronic cash system;

3. Electronic cash is divided into divisible electronic cash and indivisible electronic cash based on whether an electronic cash can be legally paid multiple times.

4. According to the use functions of electronic cash, electronic cash can be divided into special-purpose electronic cash and general-purpose electronic cash.

5. According to the use form of electronic cash, electronic cash can be divided into card-based prepaid electronic cash and purely electronic electronic cash.

2. Deposit Agreement

The merchant sends a copy of the payment agreement to the bank, (like the merchant) to verify the bank’s blind signature on the electronic cash Sign(A,B) = ( z, a, b, r) is valid. If the test passes, the bank stores (A, r 1, r 2, I s) in this database and deposits the corresponding amount of electronic cash in the merchant's account.

1. Security analysis of the solution

The security of the electronic cash system solution is based on the difficulty of calculating the discrete logarithm problem.

2. Legal electronic cash cannot be forged

Even if an illegal user withdraws k legal electronic cash from the bank as a legal user, he still cannot forge it based on the information he has obtained. The k+1th legal electronic cash, because he cannot obtain the bank’s secret private key x

3. The anonymity of legal users is guaranteed

There is a user embedded in the electronic cash The identification information (i.e. account number IU). In the payment agreement and deposit agreement, the data obtained by merchants and banks include A, B, Sign (A, B), r1, r2, among which B and r2 do not contain the user’s identification information IU. ,

And A, r1, Sign (A, B) are all the results of IU blinding. If merchants and banks want to obtain the user’s identification information (i.e. IU) from the received data, they must Knowing the blinding factor s, which is randomly selected by the user and kept secret, ensures the anonymity of electronic cash.

4. The merchant cannot forge valid payment information

In the payment agreement, although the merchant knows A, B, Sign (A, B), he can calculate d, but because he The user's secret keys u1 and s are not known, so he cannot construct r'1, r'2 at will to satisfy gr'1gr'2 AdB. Therefore, the merchant cannot forge valid payment information without the participation of legitimate users.

Baidu Encyclopedia-Postal Savings Bank of China

Baidu Encyclopedia-Electronic Cash