Title :
Recovering DC Coefficients in Block-Based DCT
Author :
Uehara, Takeyuki ; Safavi-Naini, Reihaneh ; Ogunbona, Philip
Author_Institution :
Sch. of Inf. Technol. & Comput. Sci., Wollongong Univ., NSW
Abstract :
It is a common approach for JPEG and MPEG encryption systems to provide higher protection for dc coefficients and less protection for ac coefficients. Some authors have employed a cryptographic encryption algorithm for the dc coefficients and left the ac coefficients to techniques based on random permutation lists which are known to be weak against known-plaintext and chosen-ciphertext attacks. In this paper we show that in block-based DCT, it is possible to recover dc coefficients from ac coefficients with reasonable image quality and show the insecurity of image encryption methods which rely on the encryption of dc values using a cryptoalgorithm. The method proposed in this paper combines dc recovery from ac coefficients and the fact that ac coefficients can be recovered using a chosen ciphertext attack. We demonstrate that a method proposed by Tang to encrypt and decrypt MPEG video can be completely broken
Keywords :
cryptography; discrete cosine transforms; image coding; JPEG; MPEG encryption systems; block-based DCT; ciphertext attack; cryptoalgorithm; discrete cosine transform; image quality; Compaction; Cryptography; Data security; Discrete cosine transforms; Frequency; Image coding; Image quality; Image reconstruction; Protection; Transform coding; Block DCT; image coding; image encryption; image reconstruction; multimedia data security;
Journal_Title :
Image Processing, IEEE Transactions on
DOI :
10.1109/TIP.2006.881939