| With the advancement of the information technology revolution represented by big data,artificial intelligence,cloud computing and blockchain,the value of data is further highlighted.Data has become an essential asset for individuals,enterprises,governments,and the driving force of continuous innovation.Therefore,protecting the security of data becomes increasingly important.Encryption technology allows users to encode plaintext data into ciphertext data for transmission,which is the most common and basic technical measure to ensure data security.Common encryption schemes satisfy the security under Chosen Plaintext(Ciphertext)Attacks.In the face of the coercion attack(forcing the user to provide the key or randomness used in the process of encryption)launched by the adversary,they can no longer provide confidentiality guarantee for plaintext data.Deniable encryption technology offers a feasible solution to the above problem,which allows the sender or receiver,that has performed some encrypted communication,to generate the deniable randomness or key(indistinguishable from the real value)that opens the ciphertext into another different plaintext data,thus ensuring the confidentiality of the real data.Therefore,it is of great practical significance to study the deniable encryption technology to safeguard the confidentiality of data under the coercion environment.After long-term research,deniable encryption technology has made significant progress.However,the existing deniable encryption schemes still face some challenges regarding efficiency,security,functionality and application.Firstly,deniable encryption schemes under the fully deniable model require super polynomially-long ciphertexts or use indistinguishability obfuscation technology to achieve deniability for a single bit,which is highly complex and low efficiency.Secondly,all previous deniable encryption systems are assumed to be executed by honest users and cannot prevent or detect the abuse of deniability caused by malicious users.Finally,the functionality of the existing schemes is not perfect.It cannot satisfy the authentication requirement in the electronic voting scenario,nor can they be directly applied to anonymous messaging to enhance privacy protection.The above critical issues of the deniable encryption technology are considered in this dissertation.The main study contents include:(1)Design a secure and efficient deniable encryption scheme in the fully deniable model;(2)Design a deniable encryption scheme that supports abuse detection;(3)Design a deniable encryption scheme that supports authentication;(4)Design a deniable encryption scheme for anonymous messaging.Concretely,the main contribution of this dissertation includes the following four aspects:1.The issue of enhancing the efficiency of deniable encryption schemes under the fully deniable model is explored.By introducing a tag into the encryption algorithm,a public key encryption scheme with controlled decryption is proposed,in which the ciphertexts can be decrypted by the receiver depending on the type of tag selected by the sender when encrypting.By using the pseudorandom function,a bit string position function is instantiated,which maps a n long bit string to the position of a bit 1 in the string.Based on the above encryption scheme and function,combined with the bit-flipping operation,a public-key sender-deniable encryption scheme is presented under the framework of full deniability.The scheme provides deniability for the multi-bit message,improves the length of ciphertext,and dramatically improves efficiency.Moreover,the scheme is provably secure in the standard model and provides polynomial deniable security.(Chapter 3)2.The abuse of deniability by malicious users is considered for the first time in deniable encryption.By adding an auditor and its auditing algorithm(used to detect whether the user encrypts sensitive messages beyond the permission of transmission),the formal definition and security model of abuse-resistant deniable encryption are introduced.On the basis of predicate function,and pseudorandom functions,combined with indistinguishable obfuscation technology and digital signature technology,an abuse-resistant deniable encryption scheme is proposed.The scheme allows the auditor to detect messages beyond the permission of transmission,which restricts the abuse of deniability by users.Furthermore,the scheme is provably secure and realizes super-polynomial deniability security due to the use of indistinguishable obfuscation technology.(Chapter 4)3.The functionality of authentication is considered for the first time in deniable encryption.By introducing identity and the encryption key generation algorithm for the sender,the syntax and security model of public-key authenticated deniable encryption are formally defined.By utilizing the translucent set paradigm and the idea of matchmaking encryption,a public-key authenticated deniable encryption scheme for single bit is proposed.The scheme achieves authentication by embedding identities of communication parties in the phases of encryption and decryption,and communication can be established only when both parties’identities are matched successfully.Furthermore,a public-key authenticated deniable encryption scheme for large message is constructed using the bit string position function and bit-flipping operation.These two schemes are provably secure in the random oracle model and enjoy polynomial deniable security.(Chapter 5)4.The issue of designing a deniable encryption scheme suitable for anonymous messaging is studied.By adopting the flexibly deniable model and the framework of matchmaking encryption,the formal syntax and security model of deniable matchmaking encryption are introduced.Then,by employing ideas of symmetric deniable encryption and matchmaking encryption,a deniable matchmaking encryption scheme is constructed.The scheme is provably secure in the random oracle model and enjoys bi-deniability and mutual authentication.Furthermore,the scheme allows the sender to deny the receiver’s identity,which captures the secrecy of the receiver’s identity under coercion.Based on the above scheme,public bulletin board,and Tor hidden service,an authenticated and deniable anonymous messaging framework is proposed,which not only supports anonymity and confidentiality but also uniquely provides authentication and deniability.(Chapter 6)... |
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