TECHNICAL FILED

The present disclosure relates to a method for verifying a user's opinion by use of block chain. More specifically, the present disclosure relates to the method for verifying a user's opinion, which guarantees anonymity and prevents sybil attack.

BACKGROUND

In online, there has been a lot of cases that a user provides its opinion and a receiver verifies it. Electronic voting is a representative of such cases. In addition to the electronic voting, online transactions, online contracts, online discussions, comments on online contents and the like can be the cases.

The electronic voting is conducted via an electronic terminal which is capable of electronic arithmetic operation and data processing, without voter's visiting voting place. Although the electronic voting is advantageous in terms of cost, convenience, and the wider scope of voters, it is difficult to introduce the electronic voting because there are risks of hacking, manipulation, and coercive opinion that can be caused due to remote circumstances, thereby providing little integrity in the voting process and the results thereof.

Block chain technology which is one of DLT (distributed ledger technology) can prevent the manipulation or hacking if it is applied to the electronic voting. However, because any one having a public key and a secret key can access block chain, one person can generate a large number of IDs and manipulate the voting results by misleading the opinion of the one person as being opinions of many users, also known as “sybil attack”, thereby destroying the equality of providing user's opinion.

For preventing the sybil attack, the user should be uniquely specified. Accordingly, a private information of specifying the user should be collected for guaranteeing the uniqueness. This may compromise the privacy and anonymity of the user, thereby restricting expression of free opinion. According to the present disclosure, anonymity as well as uniqueness can be guaranteed by use of homomorphic encryption which is capable of arithmetic operation of ciphertexts.

SUMMARY

The object of the present disclosure is to provide a method of verifying opinions wherein the advantages of online opinions are maintained; the disadvantages such as forgery, falsification and coercive opinion are prevented; anonymity is guaranteed; sybil attack is basically blocked; and a user can make sure that its opinion is properly reflected in the decision.

The computer-implemented method of the present disclosure, for verifying an opinion of a user is carried out in an environment including a terminal of a user who has unique identification information (IDE) generated by a process of verifying identification; and a block chain including an account module and an opinion verifying program module.

The method of the present disclosure comprises a first step of receiving, by the account module, a request for identification information of the opinion (Ballot Stamp) from the user terminal; a second step of requesting, by the account module, a first random value (RE) to the user terminal; a third step of receiving, by the account module, a first homomorphic ciphertext (HESK(RE)) which is a value of homomorphically encrypting the first random value (RE), from the user terminal; a fourth step of generating, by the account module, a second random value (RA); a fifth step of storing, by the account module, a first value which is [the second random value (RA), the first homomorphic ciphertext (HESK(RE))]; a sixth step of generating, by the account module, a second homomorphic ciphertext which is a value of homomorphically encrypting the Ballot Stamp, the second homomorphic ciphertext being one-way encrypting value of the value including first value or being a value of XOR operation to the value including the first value; a seventh step of receiving, by the account module, a third homomorphic ciphertext (HE(tag)) which is a value of homomorphically encrypting a tag, from the opinion verifying program module, the third homomorphic ciphertext (HE(tag)) being calculated by a first arithmetic operation to a random value generated by the opinion verifying program module and the second homomorphic ciphertext (HE(Ballot Stamp)); an eighth step of transmitting, by the account module, the second homomorphic ciphertext (HE(Ballot Stamp)) and the third homomorphic ciphertext (HE(tag)), to the user terminal; a ninth step of receiving, by the opinion verifying program module, the tag which is obtained by decrypting the third homomorphic ciphertext, Ballot Stamp, and the opinion message, from the user terminal; and a tenth step of determining, by the opinion verifying program module, the opinion as being verified if the value calculated by the first arithmetic operation to the random value and Ballot Stamp is identical to the tag.

The first value can further include at least one of the identification information of the account module (IDA) and the identification information of the opinion verifying program module (IDV).

The method of the present disclosure can further comprise a step of requesting, by the account module, a session for the second homomorphic ciphertext to the opinion verifying program module, between the sixth step and the seventh step. The account module can further receive the session identification information from the opinion verifying program module in the seventh step; and the account module further transmits the session identification information to the user terminal.

The random value can comprise a third random value and a fourth random value. The first arithmetic operation can include at least an operation of [one of the third random value and the fourth random value×a predetermined value±the other one of the third random value and the fourth random value].

The predetermined value can be a second homomorphic ciphertext (HE(Ballot Stamp)).

The first arithmetic operation can be XOR operation to the random value and the second homomorphic ciphertext.

According to the present disclosure, the advantages of online communication such as convenience, low cost, effectiveness and the like can be maintained; forgery, falsification, coercive opinion and sybil attack are prevented; and anonymity is guaranteed. Further, the present disclosure provides a flexibility of correcting errors and changing wrong decision, thereby making an opinion more reliable and more accurate.

