Key-Policy ABE (KP-ABE) and Comparison

In Key-Policy Attribute-Based Encryption (KP-ABE), the access policy is embedded in the user's secret key by the key authority, while ciphertexts carry sets of attributes. Decryption succeeds when the ciphertext's attribute set satisfies the policy encoded in the user's key. The authority grants decryption capabilities by choosing which policy each user's key embeds.

The foundational KP-ABE construction was presented by Goyal, Pandey, Sahai, and Waters in 2006. Their construction uses access trees where leaves are attributes and internal nodes are threshold gates. The key authority converts the access tree into a linear secret sharing scheme and encodes shares of the master secret into the user's key. Encryption is simple: choose a random secret y and distribute shares to each attribute in the ciphertext.