Patent ID: 10129029

Abstract:
Systems and methods are provided for proving plaintext knowledge of a message m, encrypted in a ciphertext, to a verifier computer. The method includes, at a user computer, encrypting the message m via a predetermined encryption scheme to produce a ciphertext u, and generating a plurality l of challenges ci, i=1 to l, dependent on the ciphertext u. For each challenge ci, the user computer generates a cryptographic proof Π2i comprising that challenge ci and a zero-knowledge proof of plaintext knowledge of the message m encrypted in the ciphertext u. The user computer sends the ciphertext u and the l proofs Π2i to the verifier computer. Each challenge ci is constrained to a predetermined challenge space C permitting identification, by searching the challenge space C, of an element ci″ such that the message m can be obtained via a decryption operation using the ciphertext u, the element ci″, and a decryption key of said encryption scheme.