Patent ID: 8817978

Claim:
An order-preserving encryption apparatus comprising: an initializer for setting a total space of a ciphertext with respect to a total space of a plaintext by considering security of the ciphertext, and setting a secret key for encryption and a pseudo-random number generator for generation of a pivot point; a pivot point generator for applying the secret key to the established pseudo-random number generator to generate a pivot point for the plaintext to be encrypted; a ciphertext generator for generating information about size of a bit constituting the ciphertext by comparing the generated pivot point and the plaintext; and a plaintext adjusting unit for dividing a total plaintext space using the pivot point, adjusting, to a total magnitude of plaintext space, a portion of the divided total plaintext space resulting in an adjusted total plaintext space, and adjusting the plaintext, wherein the ciphertext is completed by repeating from said generating the pivot point to said adjusting the plaintext for n times, said generating the pivot point performed after the resulting adjusted total plaintext space is determined from the previous round, where n is the total length of the ciphertext in bits.