Beyond Public-Key: Functional Encryption

Traditional public-key encryption follows a simple model: encrypt under a public key, decrypt with the corresponding private key. The decryptor learns the entire plaintext message. This all-or-nothing model is too coarse for many applications: a medical database might want to allow a doctor to learn only whether a patient has a specific condition, not the entire medical record. Functional encryption addresses this limitation.

Identity-Based Encryption (IBE), proposed by Shamir in 1984 and constructed by Boneh and Franklin in 2001, allows using an identity string (email address, domain name, employee ID) as a public key. A trusted key authority generates private keys for specific identities. IBE eliminates the need for public key certificates and enables simple key distribution. IBE is the simplest form of functional encryption.