KPABE

KPABE, short for Key-Policy Attribute-Based Encryption, is a form of attribute-based encryption in which the ciphertext is labeled with a set of attributes and the decryption key encodes an access policy. A user can decrypt a ciphertext if and only if the attributes attached to the ciphertext satisfy the policy encoded in the user’s key. This arrangement places the access control logic in the private key rather than in the ciphertext.

In contrast to CP-ABE (Ciphertext-Policy Attribute-Based Encryption), where the ciphertext carries the access policy and the user’s key carries attributes, KP-ABE assigns policy information to keys and attributes to ciphertexts. This makes KP-ABE suitable for scenarios in which a data owner distributes decryption capabilities to recipients according to their policies, while data is tagged with descriptive attributes.

Typical constructions involve a trusted authority that issues decryption keys corresponding to specific access structures, a setup that generates public parameters, an encryption function that tags data with a set of attributes, and a decryption function that succeeds when the ciphertext’s attributes satisfy the key’s policy. Security models usually aim for chosen-plaintext security under standard cryptographic assumptions, with some schemes offering resistance to collusion among users holding multiple keys.

Applications include fine-grained access control for outsourced or cloud-stored data, secure sharing in environments with hierarchical or group-based permissions, and scenarios requiring scalable key management where policy enforcement is delegated to users’ keys. Revocation and policy management remain practical challenges in real-world deployments.

KP-ABE emerged in the mid-2000s from work on attribute-based encryption by researchers such as Goyal, Pandey, Sahai, and Waters, with subsequent developments refining both KP-ABE and its CP-ABE counterparts.