Mergeable Functional Encryption

Vincenzo Iovino, Karol Żebrowski

In recent years, there has been great interest in Functional Encryption (FE), a generaliza-tion of traditional encryption where a token enables a user to learn a specific function of the encrypted data and nothing else. In this paper we put forward a new generalization of FE that we call M ergeable FE (mFE). In a mFE system, given a ciphertext c1 encrypting m1 and a ciphertext c2 encrypting m2, it is possible to produce in an oblivious way (i.e., given only the public-key and without knowledge of the messages, master secret-key or any other aux-iliary information) a ciphertext encrypting the string m1||m2 under the security constraint that this new ciphertext does not leak more information about the original messages than what may be leaked from the new ciphertext using the tokens. For instance, suppose that the adversary is given the token for the function f(·) defined so that for strings x ∈ {0, 1}n, f(x) 4 = g(x) for some function g: {0, 1}n → {0, 1} and for strings y = (x1||x2) ∈ {0, 1}2n, f(x1||x2) 4 = g(x1) ∨ g(x2). Furthermore, suppose that the adversary gets a ciphertext c

Saikrishna Badrinarayanan, Dakshita Khurana, Amit Sahai +1 more

Mingwu Zhang, Kirill Morozov, Tsuyoshi Takagi

Functional encryption provides a general access control over the encrypted data, where only the receiver with attribute that satisfies control policy function of policy parameter (i.e. ) can decrypt its ciphertext. Special cases of functional encryption include (anonymous-) (hierarchical) identity-based encryption, fuzzy identity-based encryption, attribute-based encryption, public key encryption with keyword search, spatial encryption, inner-product encryption, hidden-vector encryption and predicate encryption. In general functional encryption systems, the control policy function can be set flexibly. The main gap among these functional encryption schemes lies in the policy functions that associates with the secret keys. In this work, we first investigate several functional encryption schemes, and then formalize and unify the functionality description of the control policies for these schemes. After giving a general definition and security model, we present the relationship and transformations among functional encryption schemes when the equivalence of these different policy functions is employed.

Shafi Goldwasser, Steven Gordon, Vipul Goyal +6 more

Sanjam Garg, Akshayaram Srinivasan

Mehta, Arthur, Anne Müller

In a functional encryption (FE) scheme, a user that holds a ciphertext and a function key can learn the result of applying the function to the plaintext message. Security requires that the user does not learn anything beyond the function evaluation. We extend this notion to the quantum setting by providing definitions and a construction for a quantum functional encryption (QFE) scheme which allows for the evaluation of polynomialy-sized circuits on arbitrary quantum messages. Our construction is built upon quantum garbled circuits [BY22]. We also investigate the relationship of QFE to the seemingly unrelated notion of unclonable encryption (UE) and find that any QFE scheme universally achieves the property of unclonable functional encryption (UFE). In particular we assume the existence of an unclonable encryption scheme with quantum decryption keys which was recently constructed by [AKY24]. Our UFE guarantees that two parties cannot simultaneously recover the correct function outputs using two independently sampled function secret keys. As an application we give the first construction for public-key UE with variable decryption keys. Lastly, we establish a connection between quantum indistinguishability obfuscation (qiO) and quantum functional encryption (QFE); Showing that any multi-input indistinguishability-secure quantum functional encryption scheme unconditionally implies the existence of qiO.