Research On Program Obfuscation Under Virtual Black-Box Security

Obfuscation is a semantic-preserving compiler algorithm which transforms a program/circuit into an obfuscated one.While the obfuscated program preserves its functionality,the size is polynomial slowdown,and it is impossible to obtain any information from the obfuscated program.Program obfuscation has great practical value,such as strong software copyright protection,securely outsourcing computation,and sensitive proxy operation etc.It also has great research significance,some secure obfuscate functionality has been proposed,such as point function,multi-bit output point obfuscation,deniable encryption etc.In Eurocypt'01,Barak et al.gave the negative result to show that under predicate definition,it is impossible to gain a general obfuscation for all oracles or circuits.In the past few years,there are many key breakthroughs on program obfuscation.In 2007,Hohenberger proposed an obfuscator for re-encryption,and it's the first obfuscation for complicated cryptographic functionality.Then,more and more obfuscation have been constructed.In this thesis,we summed up and analyzed some obfuscation for special functionalities and constructed anonymous re-encryption functionality and designed an EVES(encrypted verifiable encrypted signature)functionality,and proposed the securely obfuscator for them respectively.The main research of our paper is as follows:(1)We introduced some obfuscation of cryptographic functionalities,analyzed the constructions of re-encryption functionality and encrypted signature functionality,and studied the models and securing proof of these two obfuscation algorithms in depth.(2)We constructed a special anonymous re-encryption functionality,and then securely obfuscated it.We proved its virtual black-box security in the random oracle models.We gave a two-form-encryption scheme that achieves the security against adaptively chosen-ciphertext attacks,when b(28)0,the ciphertext can be re-encrytped to form of b(28)1,but when b(28)1,the ciphertext cannot be re-encrypted again.The obfuscated program can be executed in any untrusted third part(e.g.,proxy,cloud server),it will not reveal any sensitive information.(3)We constructed a special EVES functionality,and securely obfuscated it,and then we proved its security.This scheme is the combine of a VES(verifiable encrypted signature)and a linear encryption scheme.The obfuscated program can be executed in any untrusted third party,it can generate a signature for the signer,and it will not reveal the secret key of the signer.