Opening a ciphertext definition
Opening a ciphertext means supplying the plaintext and randomness used dur- ing the generation of that ciphertext. In a traditional cryptosystem, encryption is binding; meaning that a given ciphertext can be opened to only the original plaintext with which it was created. In a lossy public key encryption (PKE) scheme, there are two modes of operation – injective mode and lossy mode. In the injective mode, the encryption operation is binding. In the lossy mode, if the private key is known, then a ciphertext can be opened to any plaintext of choice.