Two level QR code

to detect inauthorized duplications and to store more information

The graphical codes sensitive to coping process are very popular in product authentication domain, thanks to its easy creation, cheap production, significantly simple verification and high authentication performance. Therefore, several companies and reasearch groups look for novel authentication graphical codes to fill a gap in the market.

In 2015, we have suggested a novel security element that aims to protect valuable documents and packaging against unauthorized coping process and to store a huge amount of secret information. We call it two level barcode (2LQR). The 2LQR code stores the information in two levels: the first (public level) is readable by any barcode reader, the second (private level) is constructed by replacement of black barcode modules with specific textured patterns. This two level barcode has three strong points: 1) it stores information into two separated levels; 2) the information stored in the second level is available only to authorized users and is invisible to unauthorized users; 3) finally, this barcode could be used for printed document authentication, thanks to specific characteristics of textured patterns. Numerous experiments have been performed in order to study the storage capacity limits and reading limits depending on pattern size and pattern density. Then, additional experiments have been performed to study the barcode sensitivity to copying process.

The proposed 2LQR code can be used in two scenarious depending on textured patterns used:

• In private message sharing scenario, the textured patterns are chosen to be tolerant to print-and-scan (P&S) process and to be distinguishable one from another after it. Additionally, the samples of used textured patterns are stored in the position tags and used to decode the second storage level. If we use an 8-ary Reed-Solomon error correction code in a QR code of version 40, we can increase the hidden message length up to 20, 000 bits.
• In printed document authentication scenario, the textured patterns are chosen to be sensitive to P&S process. The authentication test proposed by us aims at verifying the printed document authenticity. If the maximal correlation values between P&S textured patterns and original numerical patterns are smaller than a predetermined authentication threshold, the printed document is considered as being counterfeited.

More deatils about the construction of two level barcode can be found in our journal paper [J2] as well as in our communications in international conferences [C4, C6]. Some security aspecs of 2LQR code were studied in international conference papers [C9, C10]. Note that the two level barcode is also patented [P1].