Funktionsverschlechterung

Functional encryption is a cryptographic paradigm that enables restricted decryption of encrypted data. In a functional encryption scheme, possessing an evaluation key associated with a function f allows the decryptor to learn f(m) from the ciphertext, where m is the plaintext, but learn nothing about m beyond what can be inferred from f(m). This contrasts with traditional public-key encryption, where decryption reveals the plaintext in full. Typically, there is a master secret key, public parameters, and a set of evaluation keys each enabling computation of a specific function on the underlying data.

Functional encryption generalizes and connects to several other cryptographic approaches. It subsumes forms such as attribute-based encryption and predicate encryption, where access to data is controlled by attributes or predicates, and it relates to fully homomorphic encryption in enabling computations over encrypted data. Some FE schemes support operations like arithmetic on ciphertexts, comparisons, or other function evaluations, making them suitable for privacy-preserving data analysis and secure data sharing.

Applications of functional encryption include secure outsourced computation, where a cloud service can compute a desired function without learning the actual data, and controlled data release, where users obtain only the information permitted by their evaluation keys. Security definitions typically require that, given an evaluation key for f, the adversary cannot learn information about the plaintext beyond f(m). Practical deployments face challenges in efficiency and key management, and research continues to develop scalable constructions and broader applicability.