Research On The Obfuscation Of Encrypted Signature Function

As a new research field in modern cryptography,obfuscation aims to construct a functionally identical program that people will be interested in.Adversary can't obtain any useful information from the new program except its usage.The aim of program obfuscation is to protect the software's intellectual property,and prevent the software from reverse engineering attacks.Besides,it can be used for secure outsourcing computing,copyright protection,sensitive proxy operations and other applications.Therefore,the extension of obfuscation technology to cryptography is a great potential in future applications.It can achieve homomorphic encryption,re-encryption,encrypted signature,undeniable encryption,transforming symmetric encryption into public key encryption.Barak et al.had demonstrated that it was impossible to idealize black-box obfuscation of general circuits.At present,the study of obfuscation in cryptography research mainly included the following two aspects: one is the construction basic function of obfuscation for hyperplane membership,point functions,conjunctions,etc.and another is the combination of the obfuscation with complex algorithmic protocols such as re-encryption,encrypted signature and other functions,constructing a special functionality of virtual black-box security obfuscation.According to the developments of obfuscation,the obfuscation results of encrypted signaturesat home and abroad will be analyzed in this paper.A specific obfuscation scheme was constructed initially for the special function of encrypted identity-based signatures.The main contents of this paper were as follows:1.Analysis the construction and features of the special obfuscation algorithms for encrypted signatures that have been existed,as well as a generic black-box obfuscation algorithm for encrypted signature function.Both advantages and disadvantages will be obtained after the comparison of the general obfuscation algorithm with fully homomorphic encryption and the former obfuscation.2.An encrypted identity-based signature(EIBS)function will be proposed,and an EIBS obfuscator will be constructed based on the Paterson's signature and Boneh's linear encryption scheme.The security of the average-case virtual black-box property will be proved.The output obfuscated circuit can be executed by any third party to implement the EIBS functionality,and the resulting ciphertext will be equivalent to the result of encrypting the signature using the receiver's public key.The security proof showed that the obfuscated circuit did not reveal the information about the signing key of the signature party,inheriting the characteristics of the identity-based signature's high efficiency and short length,and prevents the malicious private key generation center from forging the user's signature.3.The encrypted signature will be extended to signature-then-encryption function,and the signature-then-encryption function obfuscator will be constructed on the basis of the EIBS obfuscator,and the security requirements of the obfuscator also will be given.4.The encrypted blind signature obfuscator proposed by Feng et al will be studied,and the preserving functionality of obfuscator was unsatisfied,and the encrypted blind signature obfuscator will be reconstructed by using the Okamoto's blind signature scheme.The obfuscation algorithm was superior to the traditional blind signature scheme in security,and the security of preserving functionality and the virtual black-box of the new obfuscator will be demonstrated.Even if the adversary could get the obfuscated circuit and secret interaction value,the blind signature was still blind and could not be forged.