ibe

Identity-based encryption (IBE) is a type of public-key cryptography in which a user's public key is derived from a unique identifier, such as an email address, and a set of public parameters published by a trusted authority. In IBE, a trusted private key generator (PKG) holds a master secret and can issue private keys corresponding to identities, allowing anyone to encrypt messages to an identity without requiring a separate certificate for that identity.

The concept was proposed by Adi Shamir in 1984 and realized in 2001 by Boneh and Franklin using pairing-based cryptography. In typical IBE schemes, a Setup algorithm produces public parameters and a master secret. To encrypt a message for an identity ID, a sender uses ID and the public parameters to derive a ciphertext. The PKG, using its master secret, issues the private key corresponding to ID to the recipient, who can decrypt with it. Some schemes enable revocation and time-based keys (hierarchical IBE).

Advantages include simplified key management and no need for certificates. Disadvantages center on key escrow risk, since the PKG can derive any private key, and trust must be placed in the PKG and its security. Practical deployments must address secure key delivery, PKG compromise, and revocation. Security relies on hardness of underlying mathematical problems, such as bilinear pairings on elliptic curves and the random oracle model.

Variants include hierarchical IBE (HIBE), which supports a tree-like delegation of key management, and other related forms. IBE has been explored for secure email, cloud storage, and messaging, where users can receive encrypted content using only identities. Notable implementations include Boneh–Franklin IBE and subsequent enhancements in pairing-based cryptography.