Proxy Re-Encryption
Proxy re-encryption lets a semi-trusted proxy convert a ciphertext encrypted to Alice into one decryptable by Bob, while the proxy learns nothing about the plaintext.
Purpose
It enables delegated sharing of encrypted data without Alice decrypting and re-encrypting for Bob, fitting cloud-storage sharing.
Mechanism
Alice generates a re-encryption key rk_{A→B}; the proxy applies rk to C_A to produce C_B, which Bob’s private key can decrypt. rk leaks neither the plaintext nor Alice’s or Bob’s private keys. Constructions build on bilinear maps or lattices.
Use cases
- Encrypted cloud-storage sharing
- Encrypted email forwarding
- Ciphertext access delegation