White-box cryptography encryption-decryption method based on expansion ciphertext

Abstract

The invention discloses a white-box cryptography encryption-decryption method based on an expansion ciphertext. The method comprises the expansion ciphertext and a lookup table, wherein a pseudorandom bit stream is implied in the expansion ciphertext; the lookup table is used for decrypting n bits to m bits (the n is greater than the m); and a table lookup operation is a combination of three functions, namely the one-to-one mapping function F <(K, n-n)> of n-bit inputs to n-bit outputs relevant to a secret key K, the function C<n-m> of the n-bit inputs to the n-bit outputs, and the one-to-one mapping function F <(K, m-m)> of m-bit inputs to m-bit outputs relevant to the secret key K. According to the method disclosed by the invention, in encryption, a server side takes the pseudorandom bit stream as a mask, is combined with the ciphertext and is scrambled to obtain the expansion ciphertext; and in decryption, the n-bit ciphertext is decrypted into a m-bit plaintext via the table lookup operation. The decryption efficiency can be obviously improved.

Description

technical field [0001] The invention belongs to the field of information technology, and relates to a white-box cipher encryption and decryption method based on expanded ciphertext, which can be applied in untrustworthy environments such as smart phones and digital set-top boxes. Background technique [0002] Traditional cryptographic algorithms are always assumed to operate in a black-box environment at the beginning of design, that is, attackers can only observe the input and output of the algorithm. However, with the development of information technology, this assumption is no longer valid. Currently, various electronic devices are available everywhere and can directly or indirectly access the Internet, and there are more and more ways for people to obtain digital content. These devices include, but are not limited to, digital set-top boxes, IPTVs, PCs, and increasingly handheld devices such as mobile phones, tablet computers, and the like. With the intelligentization o...

AI Technical Summary

Problems solved by technology

Among them, the former has been proved to be insecure, because the lookup table of the ASASA structure has been successfully decomposed

When using SPACE to encrypt plaintext, in order to obtain good ciphertext properties, the plaintext needs to go through several rounds of encryption processing. Correspondingly, it also needs to go through several rounds of processing by the white box decryption module during decryption, and each round includes several table lookups. operation, the decryption speed is slower

Images