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A System that Scrambles Compressed Digital Contents by Code Word Permutation

IP.com Disclosure Number: IPCOM000012690D
Original Publication Date: 2003-May-21
Included in the Prior Art Database: 2003-May-21
Document File: 2 page(s) / 12K

Publishing Venue

IBM

Abstract

Disclosed is a system and method that scramble and descramble compressed and coded digital contents by semantic codeword permutation in the compressed domain.

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A System that Scrambles Compressed Digital Contents by Code Word Permutation

  Disclosed is a system and method that scramble and descramble compressed and coded digital contents by semantic codeword permutation in the compressed domain.This invention has following advantages:

1. The attribute of the contents are preserved after scrambled. For example, if the content is an MPEG2 compressed clip, it is still MPEG2 clip after scrambled. So, the scrambled contents can be viewed/checked using the normal viewer without using special tools.
2. The cost for scrambling/descrambling is very low. So, scrambling/descrambling can be done on the fly while streaming the contents.
3. The content length is completely preserved after scrambling/descrambling. So, bit rate is preserved, no buffering is necessary for streaming the scrambled/descrambled contents, and the cost of software/hardware of the scrambling/descrambling can be very low.
4. Possible number of the permutation is very large. So, security level is much higher than legacy permutation method, such as the one to scramble the codeword by using the table to exchange the codeword.
5. The permutation can be performed hierarchically. So, the security level is user selectable, such as from partial concealing to soppy scrambling. This invention consists of following points:
1. Scramble/descramble is performed in the compressed domain, within the restriction that the permutation doesn't violate the attribute of the content. Minimum unit of the permutation is semantic codeword, such as VLC for DCT (run,level), motion vector code, DC code, quantizer scale code, etc in MPEG2.
2. Permutation is also performed between sets of semantic code words. Each set consists of either same or different semantic codewords.
3. Permutation is performed hierarchically. Fig.1 depicts the structure of scrambling/descrambling system. Following is the detailed flow of the scrambling and descrambling, taking MPEG2 video clip as a sample. Scrambling:
(100) Analyze the structure of the digital "input content", which is compressed and coded.
(200) Classify codewords into groups by semantics.
(300) Create pseudo random sequence using the input "key" as the seed.
(400) Permute codewords or sets of codewords according to the pseudo random sequence and hierarchy level ("scramble level"). Following is the example of the level. Level 1: Permute the (r...