Research interest

Post-quantum cryptography

Functional encryption

 

Functional encryption (FE) is first proposed by Amit Sahai and Brent Waters in 2005 and then formalised by Dan Boneh, Amit Sahai and Brent Waters in 2010. It is a generalization of public-key encryption in which a decryption key allows a user to learn a function of the encrypted data. In functional Encryption system, for functionality F(·, ·) an authority holding a master-secret key can generate a secret-key SK k that has right to compute the function F(k, ·) on encrypted data. More precisely, using the secret-key SK k the decryptor can compute F(k, x) from an encryption of x. In contrast, an adversary gather only negligible information about x which guarantees the security of the system. More precisely, a functional encryption scheme for a given functionality F consists of the following four algorithms : ( Setup, KeyGen, Encryption, Decryption ) in which first three algorithms are randomized and the last one is deterministics algorithm. It is the generalization of several existing cryptographic primitives including Identity-Based Encryption (IBE) and Attribute-Based Encryption (ABE). For IBE, define F(k, x) to be equal to x when k corresponds to an identity that is allowed to decrypt, and ⟂otherwise. Similarly, for ABE, define F(k,x)=x when k encodes attributes with permission to decrypt and ⟂ otherwise.

 

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Cloud Computing

 

Functional encryption (FE) is first proposed by Amit Sahai and Brent Waters in 2005 and then formalised by Dan Boneh, Amit Sahai and Brent Waters in 2010. It is a generalization of public-key encryption in which a decryption key allows a user to learn a function of the encrypted data. In functional Encryption system, for functionality F(·, ·) an authority holding a master-secret key can generate a secret-key SK k that has right to compute the function F(k, ·) on encrypted data. More precisely, using the secret-key SK k the decryptor can compute F(k, x) from an encryption of x. In contrast, an adversary gather only negligible information about x which guarantees the security of the system. More precisely, a functional encryption scheme for a given functionality F consists of the following four algorithms : ( Setup, KeyGen, Encryption, Decryption ) in which first three algorithms are randomized and the last one is deterministics algorithm. It is the generalization of several existing cryptographic primitives including Identity-Based Encryption (IBE) and Attribute-Based Encryption (ABE). For IBE, define F(k, x) to be equal to x when k corresponds to an identity that is allowed to decrypt, and ⟂otherwise. Similarly, for ABE, define F(k,x)=x when k encodes attributes with permission to decrypt and ⟂ otherwise.

 

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Cloud Computing

symmetric key cryptography

Cryptography is the art and science of designing security algorithms to provide certain security services. Cryptanalysis is the art and science of analyzing and defeating the security claims of these algorithms. The branch of science that embodies both cryptography and cryptanalysis is called Cryptology. The main goal of cryptography is to secure communications between two parties (sender and receiver) by transforming a message (plaintext) into a scrambled message (ciphertext) using a secret key. The process of transforming plaintext into ciphertext is called encryption and the process of unscrambling the ciphertext to recover the original plaintext is called decryption. Modern cryptography provides the following: authentication, data integrity, and non-repudiation, to solve various aspects of information security problems.

 

Symmetric-key ciphers use one key for encryption and decryption between two parties. Thus, they require that the two communicated parties agreed beforehand on a key. The whole security of symmetric-key primitives depends on the secrecy of the key; revealing the key means that encryption and decryption are possible by anyone. Symmetric-key ciphers are used to provide the services of confidentiality and authentication and they can be divided into two schemes: block ciphers and stream ciphers. In our group, we study the cryptanalysis of symmetric ciphers in bot classical as well as the quantum framework.

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Quantum Cryptography

The journey of quantum cryptography (QC) was started in the early 1960s by Wiesner’s seminal idea of quantum money, which cannot be counterfeited. In 1984, the very first quantum key distribution protocol was proposed by Bennett and Brassard. Although QKD remains the main topic of QC, in the last few years, several other quantum cryptographic primitives are also hugely studied, like quantum secret sharing, bit commitment, private set intersection, secure direct communication, digital signatures, private query, and many more. However, the main motivation of QC is to provide an unconditional security to the cryptographic protocols. But, the information leakage through side-channels has been observed in the practical implementations of quantum cryptographic protocols. To eliminate these side-channel attacks, several security models have been proposed, such as device-independent (DI), measurement-device-independent (MDI), etc. The main goal of our research is to propose several quantum cryptographic protocols and analyze their security in the DI or MDI model.

 

 

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Private set intersection

Private set intersection (PSI) is a powerful cryptographic technique that allows two parties to compute the intersection of their data without exposing their raw data to the other party. In other words, PSI allows to test whether the parties share a common datapoint (such as a location, ID, etc). More precisely, it is a technique that enables two parties, which both have a set of data points, to compare these data sets without giving up on their individual data privacy. It is a privacy-preserving technique that allows for two parties to compute the intersection of their data. The result is a third data set with only those elements, which both parties have in common. PSI is useful for the following case: Private Contact Discovery, DNA testing and pattern matching, Remote diagnostics. In this current scenario, PSI is very useful technique to trace covid patients.

 

 

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Oblivious transfer

Oblivious transfer (OT) is an important primitive in cryptography, especially in the area of secure multi-party computation. It was first introduced by Rabin [Rab81] in 1981 to establish an exchange of secrets based on the factoring problem. The cryptographic primitive in its simplest flavour i.e 1-out-of-2 OT is carried out between two parties, a sender and a receiver. The sender has two input messages M0 and M1 and a receiver has a choice bit c. At the end of the protocol the receiver is supposed to learn the message Mc and nothing else, while the sender is supposed to learn nothing. It is an essential cryptographic tool that can serve as a building block for almost all secure multiparty functionalities and other advanced cryptographic primitives.

 

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wireless sensor network