QR碼是二維條碼的一種，在日常生活中已被廣泛地使用，QR來自英文「Quick Response」的縮寫，即快速反應，只需搭配其手機應用程式即可輕鬆解讀出其資訊，從2009開始QR碼開始在許多商務平台被當成電子票劵使用，其中包括高鐵票、電影票等等。

當QR碼被使用於票劵用途，常面臨到以下問題：票劵本身能否防偽、票卷與使用者的關係為單向與票卷本身面積過大等等。針對票卷本身能否防偽通常解決方法為在編碼方面會先將訊息經過加密處理，而使用者無法從標準解碼器解讀其資訊；為因應防偽功能而需另提供面積去放置其他資訊將造成票劵本身面積過大。基於上述問題，本文提出將傳統QR碼改良為互動式加密之雙層QR碼 (Interaction-Activated Secure Two-Layer QR codes,簡稱IASTL QR code)。此QR碼將分為兩層，第一層資訊為給使用者之資訊，可直接使用標準解碼器獲得其訊息；第二層為額外訊息需搭配使用者密碼與特殊解碼器方可得知。

本論文將分為編碼端與解碼端兩部分。編碼端部分，先將訊息利用標準編碼器編成標準QR碼，即為第一層訊息；接著將欲藏匿的資訊轉成一串有意義的序列(Sequence)，即為第二層訊息，並經過定義嵌入遮罩、加上錯誤更正碼、根據密碼不同產生對應的PN序列、產生第二層資訊之嵌入區域圖，最後依序將資訊嵌於QR碼。
在解碼端部分，將透過投影轉換(Projection transform)方法對於平面上失真之｢IASTL QR｣影像進行校正與解碼。由於傳統QR碼是由黑白兩色所組成，首先會尋找連接區域(Connected component)，接著取得傾斜之｢IASTL QR｣影像13個校正點，在透過交比(Cross ratio)得知｢IASTL QR｣影像大小及版本，並利用已知版本資訊建構出相對應棋盤格並定義13個校正點。取得傾斜｢IASTL QR｣影像校正點與棋盤格校正點即可計算出所需參數矩陣；並利用投影轉換(Projection transform)將傾斜而產生失真之｢IASTL QR｣影像更正為方正｢IASTL QR code｣，依照使用者所填入的密碼取出其第二層資訊並進一步做處理。

QR code is a type of two dimensional barcode that has been widely used in our daily life. QR is the abbreviation of the “Quick Response,” which means instantaneous response. When it is scanned with applications installed in smartphones, quick decoding can be achieved. Since 2009, QR code is used for electronic ticket at the widely electronic commerce platform which includes High Speed Rail and movie ticket.

QR code ticket will confront some problems as ticket. The problems are as followed, the first problem is ticket security, the second problem that the relationship between the ticket and the user is one way and the third problem is that the ticket area is too large. QR code is common solution for ticket security that the user can’t use standard QR decoder to decode the message after encryption. For these reason, this research will propose to modify the traditional QR code for the two-layer security QR code. The first layer of information is for user’s message and the second layer of information which is the special message can decode with the special decoder

The research divides into encoder part and decoder part. In encoder part, we will hid some message which transform into meaningful sequence, defined the hidden mask and adds error correction code. Next the PN sequence is generated according to the different password, generated the QR map and we finally hid the serial sequence into each module on QR code.

In decoder part, we try to decode and correct the distorted QR code in plane through the projective transform. Due to the traditional QR code is consisted of black and white module. We search the connected component at first, get the thirteen corrected points of the distorted QR code and obtain the QR which is version and size through the method of cross ratio. We generate the corresponding checkerboard according to the known version and size and the thirteen corrected points. The distorted QR code transforms into the square QR code through the parameter matrix. Final step we extract the second layer information and process according to the password of the user’s input.

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