The primitive of proofs of ownership (PoWs) enables a prover to efficiently convince a verifier that he/she indeed owns a certain message in a knowledge-proof manner. As a result, it can prevent an adversary who only has a short information of the message from accessing the whole one. We argue that the existing PoWs based on Merkle hash tree and specific encodings are not much efficient if the size of message is sufficiently huge. In this paper, we first propose a new PoW protocol based on the chameleon hash function without key exposure. Interestingly, it is equivalent to having the prover compute a new collision of chameleon hashing as the proof in our construction. Therefore, the proposed protocol is much efficient since the computation and storage overhead of proof is independent of the size of the message. Moreover, we utilize the proposed PoWs to design a deduplication scheme over ciphertext.