視覺密碼中不擴展的(k, n)門檻值秘密影像分享方法之研究

A Study of (k, n)-threshold Secret Image Sharing Schemes in Visual Cryptography without Expansion.

陳瀅羽(Ying-Yu Chen)

指導教授 ： 阮夙姿

國立暨南國際大學/科技學院/資訊工程學系/碩士(2011年)

https://doi.org/10.6837/NCNU.2011.00108

摘要

視覺密碼 (Visual cryptography)，是將一張秘密影像加密分成n張片段 (share)；當只拿到任何一張片段時，並無法得知秘密影像中的內容，一定要將所有片段疊合起來，才會顯示秘密影像中內容。而(k, n)-門檻機密分享機制 ((k, n)-threshold secret sharing) 則同樣將秘密影像加密分成n張片段，但在解密時，只需任何k張片段做疊合就可顯示秘密影像；反之，當疊合片段張數少於k時，則無法得知秘密影像中的內容。其中，在此機制下有個很重要的參數:'a'，如果'a'越大，就代表疊合後顯示的秘密影像越清楚。另外，漸進式視覺機密分享 (progressive visual secret sharing)，是如果疊合越多張片段，疊合出的影像就會越明顯的機密分享機制。
本論文主要研究成果是提出一種視覺密碼中像素不需擴展的(k, n)-門檻機密分享機制；此方法是利用組合學的概念所設計出的。對於視覺密碼中的(k, n)-門檻機密分享機制，過去大部分學者的所提出的方法，其像素皆會擴展。本論文提出對任意正整數n >= k >= 2時，一種像素不擴展，且'a'值較前人所提出的更好，也就是說還原後的影像將更清楚的(k, n)-門檻機密分享機制。由於還原影像時，將會滿足越多張片段時影像越清楚。因此本文針對任意二正整數n >= k >= 2，提出的(k, n)-門檻機密分享機制，可達像素不擴展、有較好的?值且是漸進式視覺機密分享之三項優勢。

關鍵字

視覺密碼 ； (k, n)-門檻 ； 機密分享 ； 漸進式 ； 資訊安全 ； 片段

並列摘要

Visual cryptography (VC, for short) encrypts the secret image into n shares (transparency). In this way, we cannot see any information from any one share, and decrypt the original image by stacking all of the shares. In this thesis, we extend it to the k out of n secret sharing scheme, (k, n)-threshold secret sharing scheme, which encrypts the secret image in the same way, but decrypts
the original image by stacking at least k shares. If one stacks less than k shares, one cannot recognize the secret image. An important parameter when discussing a secret sharing scheme in VC is contrast 'a'. If 'a' is larger, the recoverd image is clearer. Another subject is progressive visual secret sharing, that means when more shares are stacked progressively, the combined share will be clearer.
In this thesis, we construct a new (k, n)-threshold secret sharing scheme in VC for any positive integers n >= k >= 2 by using a method of combination, and the size of each share is as small as the original image. That is, there is no expansion needed while some of the previous scheme need. In the same time, our scheme has better contrast 'a' than previous method and it is also a (k, n)-threshold progressive visual secret sharing scheme.

並列關鍵字

visual cryptography ； (k, n)-threshold ； secret sharing ； progressive ； information security ； share

參考文獻

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