CN108494559B - Electronic contract signing method based on semi-trusted third party - Google Patents

Electronic contract signing method based on semi-trusted third party Download PDF

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CN108494559B
CN108494559B CN201810198446.8A CN201810198446A CN108494559B CN 108494559 B CN108494559 B CN 108494559B CN 201810198446 A CN201810198446 A CN 201810198446A CN 108494559 B CN108494559 B CN 108494559B
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party
signature
contract
digital signature
arbitrator
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CN108494559A (en
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罗喜伶
王震
周泽全
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Beihang University
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Beihang University
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
    • H04L9/32—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols including means for verifying the identity or authority of a user of the system or for message authentication, e.g. authorization, entity authentication, data integrity or data verification, non-repudiation, key authentication or verification of credentials
    • H04L9/3247—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols including means for verifying the identity or authority of a user of the system or for message authentication, e.g. authorization, entity authentication, data integrity or data verification, non-repudiation, key authentication or verification of credentials involving digital signatures
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06Q—INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR ADMINISTRATIVE, COMMERCIAL, FINANCIAL, MANAGERIAL OR SUPERVISORY PURPOSES; SYSTEMS OR METHODS SPECIALLY ADAPTED FOR ADMINISTRATIVE, COMMERCIAL, FINANCIAL, MANAGERIAL OR SUPERVISORY PURPOSES, NOT OTHERWISE PROVIDED FOR
    • G06Q30/00—Commerce
    • G06Q30/018—Certifying business or products
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
    • H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
    • H04L9/0816—Key establishment, i.e. cryptographic processes or cryptographic protocols whereby a shared secret becomes available to two or more parties, for subsequent use
    • H04L9/0819—Key transport or distribution, i.e. key establishment techniques where one party creates or otherwise obtains a secret value, and securely transfers it to the other(s)
    • H04L9/0825—Key transport or distribution, i.e. key establishment techniques where one party creates or otherwise obtains a secret value, and securely transfers it to the other(s) using asymmetric-key encryption or public key infrastructure [PKI], e.g. key signature or public key certificates
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
    • H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
    • H04L9/0816—Key establishment, i.e. cryptographic processes or cryptographic protocols whereby a shared secret becomes available to two or more parties, for subsequent use
    • H04L9/0819—Key transport or distribution, i.e. key establishment techniques where one party creates or otherwise obtains a secret value, and securely transfers it to the other(s)
    • H04L9/083—Key transport or distribution, i.e. key establishment techniques where one party creates or otherwise obtains a secret value, and securely transfers it to the other(s) involving central third party, e.g. key distribution center [KDC] or trusted third party [TTP]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
    • H04L9/14—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols using a plurality of keys or algorithms
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
    • H04L9/32—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols including means for verifying the identity or authority of a user of the system or for message authentication, e.g. authorization, entity authentication, data integrity or data verification, non-repudiation, key authentication or verification of credentials
    • H04L9/321—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols including means for verifying the identity or authority of a user of the system or for message authentication, e.g. authorization, entity authentication, data integrity or data verification, non-repudiation, key authentication or verification of credentials involving a third party or a trusted authority

Abstract

The invention relates to an electronic contract signing method based on a semi-trusted third party, which mainly adopts the technical means of cryptography to ensure the safety and fairness of electronic contract signing. And when signing, the contract initiator A firstly generates a digital signature of the contract initiator A, then performs double encryption and sends the double encrypted signature to the other party B, and if the encrypted signature is valid, both parties can exchange the digital signature to finally complete signing of the contract. If any disputes occur, a third party (arbitrator) may be applied for arbitration and to assist in completing the contract subscription. In the process of contract signing, a third party (arbitrator) is offline and semi-credible, namely the third party (arbitrator) is introduced only when disputes occur, and in the process of arbitration, the third party (arbitrator) cannot obtain the original signatures of both contract signing parties, so that the possibility that the third party (arbitrator) reveals digital signatures is avoided, and therefore the method has strong guarantee on efficiency and safety.

Description

Electronic contract signing method based on semi-trusted third party
Technical Field
The invention relates to the technical field of electronic commerce and cryptography, in particular to an electronic contract signing method based on a semi-trusted third party.
Background
With the development of the internet, electronic commerce gradually becomes a new economic development mode, and an electronic contract is used as a link in the electronic commerce and is rapidly developed by the characteristics of simplicity, convenience and flexibility. The electronic contract can be signed by two mutually-acquainted parties through the electronic technology and the Internet as media, and compared with the traditional signing mode, the electronic contract has the characteristics of rapidness, simplicity, convenience, easiness in storage and the like, so that the electronic contract has a good development prospect.
However, there are many insecure factors in the internet, and hacker attacks, network eavesdropping, and fraudulent activities can greatly harm the security and fairness of electronic contracts. Electronic contracts generally relate to business confidentiality, and once contract or user information is leaked, the consequences are unimaginable, so that the realization of the security and fairness of electronic contracts is a prerequisite for the development of electronic contract technologies. At present, most schemes adopt technologies such as digital signatures and the like to ensure the integrity of electronic contract contents, but the schemes only consider the integrity of the contract contents and do not consider the security of the digital signatures of users, the digital signatures are equivalent to hand-written signatures, and once the digital signatures are revealed, the benefits of the users are damaged; secondly, most schemes require an online third party to complete contract exchange, and the scheme efficiency is not high for a system with a large number of users; finally, the above scheme requires complete trust for the third party, and once the third party is attacked, the user information is necessarily leaked.
Therefore, aiming at the defects and shortcomings of the electronic contract signing method, the invention provides the electronic contract signing method based on the semi-trusted third party, which improves the efficiency of signing the electronic contract and ensures the safety and fairness of the electronic contract content and the digital signature of the user.
Disclosure of Invention
The invention provides an electronic contract signing method based on a semi-trusted third party, which adopts the technical means of combining digital signature with public key encryption and the like, simultaneously comprises an arbitration mechanism of the semi-trusted third party and aims to solve the problems of low safety, fairness and efficiency and the like in the electronic contract signing process at present.
An electronic contract signing method based on a semi-trusted third party comprises the following steps:
s1: both parties of the contract (A, B) confirm to sign the electronic contract, both parties disclose the contract document, at the same time, both parties register in the electronic contract system by using the identity information to obtain respective signature keys for generating respective digital signatures;
s2: A. b and the third party (arbitrator) register in CA (authentication center) center separately, get their own cipher key pair, include a public key and a private key, the public key is used for encrypting the digital signature, the private key is used for deciphering;
s3: the contract initiator A firstly generates a digital signature about the contract by using a signature key of the contract initiator A, and doubly encrypts the digital signature by using the public keys of the party B and a third party (an arbitrator) to obtain an encrypted digital signature and sends the encrypted digital signature to the party B;
s4: if B does not receive the digital signature of A or receives the signature which is verified to be invalid, B terminates signing of the contract; otherwise, B uses its own signature key to generate digital signature about contract, and sends it to A;
s5: if A does not receive the digital signature of B or receives the digital signature which is verified to be invalid, A terminates the signing of the contract; otherwise, the A sends the digital signature to the B, the B verifies the digital signature, and if the signature of the A is valid, the signing of the contract is completed; otherwise, entering an arbitration stage;
s6: b first encrypts its digital signature with the public key of a to obtain an encrypted signature, and submits the encrypted signature to a third party (arbiter) for arbitration together with the encrypted signature sent by a at S2.
As a further supplement to the present invention, the electronic contract system and the CA center are separated, and are respectively responsible for different authorities and mutual noninterference, the electronic contract system is responsible for contract signing, the CA center is only responsible for maintenance and distribution of user keys, and a third party (arbitrator) responsible for arbitrating transactions belongs to the electronic contract system. The authority separation strategy reduces the workload of the CA center, improves the scheme efficiency, reduces interference factors in the electronic contract signing process, and improves the safety.
As a further supplement to the present invention, the digital signature for signing an electronic contract is based on an identity cryptosystem, that is, the signature key of the user is related to the identity information of the user, and the identity information includes the user's identity number, mobile phone number, mailbox, address, and biometric information (fingerprint, iris), etc. The signature key of the user is used for generating the digital signature, the system parameters and the public key are used for verifying the digital signature, the verification is successful, the digital signature is valid, the contract content is not tampered, and the identity of the contract signer is valid.
As a further supplement to the present invention, when the contracting parties (A, B) and the third party (arbitrator) register with the CA center, the CA center generates a pair of keys for them, the private key is sent to the user through short message, mail or other private channel, and the public key is provided with a corresponding digital certificate for proving the validity of the key. The public key is used for encrypting the digital signature, the encrypted signature is firstly sent when signing, and after the signature is verified to be valid, both parties sign a contract. The private key is used for decryption, and when rights and interests disputes or fraud behaviors occur, the private key can be used for decryption to recover the digital signature of the other party, so that the signing of the electronic contract is completed.
As a further supplement to the present invention, in step S3, the contract initiator a first needs to perform double encryption on the digital signature generated by the contract initiator a, that is, after encrypting the digital signature by using the public key of B, the second layer of encryption is performed by using the public key of the third party (arbiter), and the order of the two layers of encryption can be changed.
As a further supplement of the present invention, when both parties of the contract receive the digital signature or the encrypted signature of the other party, the public key of the other party is firstly required to be used for verification, if the signature is valid, the next step is carried out, when the encrypted signature is verified, decryption is not required, and if the encrypted signature is valid, the original digital signature is also valid; otherwise, the signature is invalid.
As a further supplement to the present invention, the third party (arbitrator) in the present invention is in an offline state, and appears only when the two parties dispute, i.e. in step S6, to resolve disputes and assist the two parties in completing contract signing. The offline third party (arbitrator) has a significant increase in efficiency compared to the online third party in most current schemes, since it does not need to directly participate in the contract-signing process.
As a further supplement to the present invention, in step S6, i.e. during the arbitration phase, the third party (arbiter) first verifies whether the two encrypted signatures sent by B are valid, and if any encrypted signature is invalid, the third party rejects the arbitration application; otherwise, if the two are both effective, the third party (arbiter) utilizes the private key of the third party to carry out first-layer decryption, and the results are respectively sent to A and B; and B, carrying out second-layer decryption by using the private key of the B to obtain the original digital signature of A, thereby completing signing of the electronic contract. During arbitration, the two layers of decryption order cannot be changed.
As a further supplement to the present invention, the third party (arbitrator) in the invention is semi-trusted, that is, the third party (arbitrator) does not directly participate in the exchange of digital signatures during the whole contract signing process, and the third party (arbitrator) does not know the original digital signatures of both parties, so that the possibility that the third party (arbitrator) reveals the digital signatures of both parties of the contract is reduced, and the security is improved.
The electronic contract signing method based on the semi-trusted third party provided by the invention adopts the digital signature technology based on the identity to ensure the integrity of contract content and the validity of the identities of both parties of the contract, adopts the public key encryption technology to encrypt the digital signature to ensure the safety and the confidentiality of the digital signature, and ensures the high efficiency and the fairness of contract signing through the arbitration mechanism of the semi-trusted off-line third party (arbiter), thereby completing the electronic contract signing more efficiently and more safely and playing a positive role in the development of electronic contracts and even electronic commerce.
Drawings
Fig. 1 is a flowchart of an electronic contract signing method based on a semi-trusted third party according to an embodiment of the present invention.
Detailed Description
In order to make the objects, aspects and effects of the embodiments of the present invention clearer and clearer, the present invention is further described in detail below by way of examples with reference to the accompanying drawings.
The attached drawing is a flow chart of the electronic contract signing method based on the semi-trusted third party provided by the invention. As shown in fig. 1, the present invention comprises the following steps:
s1: the contract parties (A, B) confirm the electronic contract, and the contract documents are disclosed, and the contract parties register with the identity information in the electronic contract system.
Upon receiving the willingness of the parties to sign an electronic contract, the system generates the following parameters. Selecting two finite cyclic groups G and G of order pTAnd e: g → GTIs a bilinear map and G is the generator of the cyclic group G. User identity length is set to nuAnd identity information is recorded as
Figure GDA0002761095030000041
Wherein for 0 < i ≦ nuThere is ui ∈ {0, 1 }. If uiUnder 1, the index i is taken into the set
Figure GDA0002761095030000042
In (1). Randomly selecting nuDimension vector U ═ Ui)，nmDimension vector M ═ Mj) And the element u ', m' e.g. G, where ui，mjIs a random element in group G. Is provided with ZpRandomly selecting alpha for integer cyclic groups of order p1∈Zp，g2E G, set
Figure GDA0002761095030000043
Let A, B register as uA、uBRandomly selecting alpha1∈ZpThen the signing key of A, B is
Figure GDA0002761095030000044
S2: A. b and the third party (arbitrator) are respectively registered in a CA (certification center) center, and the CA center comprises a key generator for generating key pairs of the two parties of the contract and the third party (arbitrator). Is provided with ZpIs a cyclic group of p-order integers, randomly selecting alphaA，αB，αT∈ZpThen A, B and the key pair of the third party (arbiter) are respectively
Figure GDA0002761095030000045
Figure GDA0002761095030000046
And
Figure GDA0002761095030000047
wherein PKA、PKBAnd PKTIs a public key used for encrypting digital signatures, SKA、SKBAnd SKTIs a private key used to decrypt the digital signature.
S3: the contract initiator A firstly generates a digital signature about the contract by using the own signature key, and when the digital signature is generated, n is generated by using a digital digest algorithmmSummary of electronic contract documents of length
Figure GDA00027610950300000412
Wherein for 0 < j ≦ nmHas m ofjE {0, 1 }. If mjLet the subscript j be taken together as 1
Figure GDA0002761095030000048
In (1). Then the system randomly selects
Figure GDA00027610950300000411
Calculating digital signature by using signature key of A
Figure GDA0002761095030000049
Wherein sigmaA，0，σA，1，σA，2For digital signature σAThree components of (a). Then A uses public keys of B and a third party (arbitrator) to carry out double encryption on the digital signature, and when carrying out double encryption, the public keys PK of the third party (arbitrator) and B are firstly usedT，PKBGenerating a new public key
Figure GDA00027610950300000410
Randomly selecting t ∈ ZpThen calculates the encrypted signature
Figure GDA0002761095030000051
Figure GDA0002761095030000052
ωA＝(ωA，1，ωA，2，ωA，3，ωA，4).
Wherein ω isA，1，ωA，2，ωA，3，ωA，4For encrypted signatures omegaAFour components of. Finally A will be omegaAAnd sending the data to B.
S4: after receiving the encrypted signature sent by a, B verifies it using the following formula.
Figure GDA0002761095030000053
Where e is a bilinear map. If the formula is established, the signature is valid; otherwise, the signature is invalid.
If B does not receive the digital signature of A or receives the signature which is verified to be invalid, B terminates signing of the contract; otherwise, B generates a digital signature for the contract using its own signing key. When generating digital signature, n is generated by using digital digest algorithmmSummary of electronic contract documents of length
Figure GDA0002761095030000054
Wherein for 0 < j ≦ nmHas m ofjE {0, 1 }. If mjLet the subscript j be taken together as 1
Figure GDA0002761095030000055
In (1). Then the system randomly selects
Figure GDA0002761095030000056
Computing a digital signature of B
Figure GDA0002761095030000057
Wherein sigmaB，0，σB，1，σB，2For digital signature σBThree components of (a). B then sends the digital signature to a.
S5: after receiving the digital signature of B, a verifies using the following formula.
Figure GDA0002761095030000058
Where e is a bilinear map. If the formula is established, the signature is valid; otherwise, the signature is invalid.
If A does not receive the digital signature of B or receives the digital signature which is verified to be invalid, A terminates the signing of the contract; otherwise, the A sends the digital signature to the B, the B verifies the digital signature, and if the signature of the A is valid, the signing of the contract is completed; otherwise, enter the arbitration phase.
S6: b first uses the public key PK of AAAnd encrypting the digital signature of the user to obtain the encrypted signature. During encryption, the system randomly selects t' to be belonged to ZpThen calculate
Figure GDA0002761095030000061
Figure GDA0002761095030000062
ωB＝(ωB，1，ωB，2，ωB，3，ωB，4).
Wherein ω isB，1，ωB，2，ωB，3，ωB，4For encrypted signatures omegaBFour components of (1). Then B will be ωBAnd a cryptographic signature ω sent at stage S2ASubmitted to a third party (arbitrator) for arbitration.
The third party (arbiter) receives the omega sent by BAAnd ωBThereafter, first, whether the signature is valid is verified using the following formula.
Figure GDA0002761095030000063
Figure GDA0002761095030000064
Where e is a bilinear map. If two formulas have anyIf not, the third party (arbitrator) refuses the arbitration request of B; otherwise, the third party (arbiter) utilizes its private key SKTFor omegaAThe first layer of decryption is performed,
Figure GDA0002761095030000065
Figure GDA0002761095030000066
ω′A＝(ω′A，1，ω′A，2，ω′A，3，ω′A，4).
the third party (arbiter) will then ω'AIs sent to B while ω is sentBAnd sending the signal to A. B received ω'AThereafter, use its private key PKBPerform decryption and calculation
Figure GDA0002761095030000067
Figure GDA0002761095030000068
σA＝(σA，0，σA，1，σA，2).
Finally, the digital signature sigma of A is obtainedAThereby completing the signing of the electronic contract.
In the above embodiment, all the calculations are completed by the electronic contract system, and the user only needs to perform corresponding operations on the corresponding platform, so that the method has good practicability. In the whole process, a semi-trusted third party (arbitrator) only arbitrates when two parties dispute or fraud behaviors, and original digital signatures of the two parties are not contacted all the time, so that the fairness of contract signing can be ensured, and the identity privacy of a user can be effectively protected.
The foregoing is a more detailed description of the invention, taken in conjunction with the detailed description, and it is to be understood that the embodiments described are only a few examples, but not all examples, of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Claims (8)

1. An electronic contract signing method based on a semi-trusted third party is characterized by comprising the following steps:
s1: both parties of the contract (A, B) confirm the signing of the electronic contract, both parties disclose the contract document, and both parties register in the electronic contract system by using the identity information, and the system selects two limited cycle groups G and G with the order pTAnd e: g → GTIs a bilinear mapping, G is the generator of cyclic group G, and the user identity length is set as nuAnd identity information is recorded as
Figure FDA0002761095020000011
Wherein for 0 < i ≦ nuHas uiE.g., {0, 1}, if uiUnder 1, the index i is taken into the set
Figure FDA0002761095020000012
Performing the following steps; randomly selecting nuDimension vector U ═ Ui)，nmDimension vector M ═ Mj) And the element u ', m' e.g. G, where ui，mjIs a random element in group G; is provided with ZpRandomly selecting alpha for integer cyclic groups of order p1∈Zp，g2E G, set
Figure FDA00027610950200000112
Let A, B register as uA、uBRandomly select ru∈ZpThen the signing key of A, B is
Figure FDA0002761095020000013
S2: A. b and the third party (arbitrator) register in CA (authentication center) center separately, CA center include a key generator, is used for producing the key pair of both sides of contract and third party (arbitrator); is provided with ZpIs a cyclic group of p-order integers, randomly selecting alphaA，αB，αT∈ZpThen A, B and the key pair of the third party (arbiter) are respectively
Figure FDA0002761095020000014
Figure FDA0002761095020000015
And
Figure FDA0002761095020000016
wherein PKA、PKBAnd PKTIs a public key used for encrypting digital signatures, SKA、SKBAnd SKTIs a private key for decrypting the digital signature;
s3: the contract initiator A firstly generates a digital signature about the contract by using the own signature key, and when the digital signature is generated, n is generated by using a digital digest algorithmmSummary of electronic contract documents of length
Figure FDA0002761095020000017
Wherein for 0 < j ≦ nmHas m ofjE.g. {0, 1}, if mjLet the subscript j be taken together as 1
Figure FDA00027610950200000111
Performing the following steps; then the system randomly selects
Figure FDA0002761095020000018
Calculating digital signature by using signature key of A
Figure FDA0002761095020000019
Wherein sigmaA，0，σA，1，σA，2For digital signature σAThe three components of (a); then A uses public keys of B and a third party (arbitrator) to carry out double encryption on the digital signature, and when carrying out double encryption, the public keys PK of the third party (arbitrator) and B are firstly usedT，PKBGenerating a new public key
Figure FDA00027610950200000110
Randomly selecting t ∈ ZpThen calculates the encrypted signature
Figure FDA0002761095020000021
ωA，2＝gt，
Figure FDA0002761095020000022
ωA＝(ωA，1，ωA，2，ωA，3，ωA，4)
Wherein ω isA，1，ωA，2，ωA，3，ωA，4For encrypted signatures omegaAAnd finally A will be ωASending the data to B;
s4: after receiving the encrypted signature sent by A, B performs verification by using the following formula:
Figure FDA0002761095020000023
wherein e is bilinear mapping, and if the formula is established, the signature is valid; otherwise, the signature is invalid;
if B does not receive the digital signature of A or receives the signature which is verified to be invalid, B terminates signing of the contract; otherwise, B uses own signature key to generate digital signature about contract; in the generation ofWhen the digital signature is carried out, n is generated by using a digital digest algorithmmSummary of electronic contract documents of length
Figure FDA0002761095020000024
Wherein for 0 < j ≦ nmHas m ofjE.g. {0, 1}, if mjLet the subscript j be taken together as 1
Figure FDA0002761095020000028
Performing the following steps; then the system randomly selects
Figure FDA0002761095020000025
Computing a digital signature of B
Figure FDA0002761095020000026
Wherein sigmaB，0，σB，1，σB，2For digital signature σBThen B sends the digital signature to A;
s5: after receiving the digital signature of B, A is verified by the following formula:
Figure FDA0002761095020000027
wherein e is bilinear mapping, and if the formula is established, the signature is valid; otherwise, the signature is invalid;
if A does not receive the digital signature of B or receives the digital signature which is verified to be invalid, A terminates the signing of the contract; otherwise, the A sends the digital signature to the B, the B verifies the digital signature, and if the signature of the A is valid, the signing of the contract is completed; otherwise, entering an arbitration stage;
s6: b first uses the public key PK of AAEncrypting the digital signature of the system to obtain the encrypted signature, and randomly selecting t' belonged to Z during encryption by the systempThen calculate
Figure FDA0002761095020000031
ωB，2＝gt′，
Figure FDA0002761095020000032
ωB＝(ωB，1，ωB，2，ωB，3，ωB，4)
Wherein ω isB，1，ωB，2，ωB，3，ωB，4For encrypted signatures omegaBThen B will be ωBAnd a cryptographic signature ω sent at stage S2ASubmitting to a third party (arbitrator) to apply for arbitration;
the third party (arbiter) receives the omega sent by BAAnd ωBThen, first, the signature is verified to be valid using the following formula:
Figure FDA0002761095020000033
Figure FDA0002761095020000034
wherein e is bilinear mapping, if any of the two formulas is not satisfied, the third party (arbiter) rejects the arbitration request of B; otherwise, the third party (arbiter) utilizes its private key SKTFor omegaAThe first layer of decryption is performed,
Figure FDA0002761095020000035
ω′A，2＝ωA，2＝gt，
Figure FDA0002761095020000036
ω′A＝(ωA，1，ωA，2，ωA，3，ωA，4).
the third party (arbiter) will then ω'AIs sent to B while ω is sentBSending the signal to A; b received ω'AThereafter, use its private key PKBPerform decryption and calculation
Figure FDA0002761095020000037
Figure FDA0002761095020000038
σA＝(σA，0，σA，1，σA，2).
Finally, the digital signature sigma of A is obtainedAThereby completing the signing of the electronic contract.
2. The method of claim 1, wherein the electronic contract system and the CA center are separated and each is responsible for different authorities without mutual interference, the electronic contract system is responsible for contract signing, the CA center is responsible only for maintenance and distribution of the user key, and the third party (arbitrator) responsible for arbitrating the transaction belongs to the electronic contract system.
3. A method as claimed in claim 1, characterised in that the contracting parties (A, B) and the third party (arbitrator) are registered with the CA centre, for which the CA centre generates a pair of keys, the private key being sent to the user via sms, mail or other private channel, and the public key being provided with a corresponding digital certificate for certifying the legitimacy of the keys.
4. The method as claimed in claim 1, wherein in step S3, the contract initiator a first needs to perform double encryption on the generated digital signature, the double encryption is performed by using the public key of B to perform encryption on the digital signature, and then by using the public key of a third party (arbitrator) to perform the second layer encryption, and the order of the two layers of encryption can be changed.
5. The method of claim 1, wherein, when receiving the digital signature or encrypted signature of the other party, the two parties of the contract first need to verify by using the public key of the other party, if the signature is valid, then proceed to the next step, when verifying the encrypted signature, no decryption is needed, if the encrypted signature is valid, then the original digital signature is also valid; otherwise, the signature is invalid.
6. The method of claim 1, wherein the third party (arbitrator) is offline and occurs only when the two parties dispute (S6) to resolve the dispute and assist the two parties in contracting.
7. The method according to claim 1, wherein in step S6, i.e. the arbitration phase, the third party (arbiter) first verifies whether the two encrypted signatures sent by B are valid, and if any encrypted signature is invalid, the third party rejects the arbitration application; otherwise, if the two are both effective, the third party (arbiter) utilizes the private key of the third party to carry out first-layer decryption, and the results are respectively sent to A and B; and B, carrying out second-layer decryption by using the private key of the B to obtain the original digital signature of A, thereby completing signing of the electronic contract.
8. The method of claim 1, wherein the third party (arbitrator) is semi-trusted, i.e., the third party (arbitrator) does not directly participate in the exchange of digital signatures throughout the contract-signing process, and the third party (arbitrator) does not know the original digital signatures of both parties.
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