1.School of Chemical Science and Engineering, Shanghai Research Institute for Intelligent Autonomous Systems, Key Laboratory of Advanced Civil Engineering Materials of Ministry of Education, Tongji University, Shanghai 200092, China 2.Shanghai Synchrotron Radiation Facility, Zhangjiang Laboratory, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201800, China 3.School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
Fund Project:Project supported by the National Key R&D Program of China (Grant Nos. 2016YFA0400900, 2016YFA0201200), the National Natural Science Foundation of China (Grant Nos. 21722310, 21834007, 21873071, 91953106), and the Fundamental Research Fund for the Central Universities, China
Received Date:30 August 2020
Accepted Date:03 November 2020
Available Online:03 March 2021
Published Online:20 March 2021
Abstract:The fabrication of precise arrays of atoms is a key challenge at present. As a kind of biomacromolecule with strict base-pairing and programmable self-assembly ability, DNA is an idea material for directing atom positioning on predefined addresses. Here in this work, we propose the construction of iron atom arrays based on DNA origami templates and illustrate the potential applications in cryptography. First, ferrocene molecule is used as the carrier for iron atom since the cyclopentadienyl groups protect iron from being affected by the external environment. To characterize the iron atom arrays, streptavidins are labelled according to the ferrocene-modified DNA strand through biotin-streptavidin interactions. Based on atomic force microscopy scanning, ferrocene-modified single-stranded DNA sequences prove to be successfully immobilized on predefined positions on DNA origami templates with high yield. Importantly, the address information of iron atoms on origami is pre-embedded on the long scaffold, enabling the workload and cost to be lowered dramatically. In addition, the iron atom arrays can be used as the platform for constructing secure Braille-like patterns with encoded information. The origami assembly and pattern characterizations are defined as encryption process and readout process, respectively. The ciphertext can be finally decoded with the secure key. This method enables the theoretical key size of more than 700 bits to be realized. Encryption and decryption of plain text and a Chinese Tang poem prove the versatility and feasibility of this strategy. Keywords:DNA origami/ atom array/ self-assembly/ cryptography
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4.基于铁原子阵列图案的信息加密从本文铁原子阵列的制备和表征过程可以看出, 信息链预置于骨架链的思路不仅是对骨架链的预保护, 实际上也等同于将信息链隐藏于骨架链上; 此外, 信息的写入(杂交)和读取(成像)在物理上是分开的, 并且由两个不同的实体进行. 因此, 基于以上技术, 使开发基于铁原子阵列的信息加密技术成为可能. 在前期开发的DNA折纸加密(DOC)技术基础上, 本文利用铁原子阵列提出了原子阵列DNA折纸加密(A-DOC)技术. 如图3(a)所示, 发送方和接收方(分别命名为Alice和Bob)利用A-DOC技术进行了文本信息的秘密传递, 其原理是对折纸上不同的铁原子位置编码, 通过密钥进行加密, 并结合隐写术加强保密程度. 首先, 使用密钥对二进制文本进行加密, 转换成折纸上的原子点阵图案. 在第二步, 将对应该点阵的信息链与骨架链进行杂交, 得到的样品即包含了秘密传递的信息. Alice将预置M链的骨架链交付给Bob, Bob再将通用订书钉链库与骨架链进行退火组装, 获得折纸结构. 值得注意的是, Bob获得的折纸虽然已隐藏了秘密信息, 但需要在结合二茂铁修饰序列, 形成铁原子阵列后, 才能通过成像手段将隐写图案进行读取. 最后, Bob通过密钥将读取的原子点阵图案进行解密, 获得明文. 图 3 DNA折纸加密及编码原理示意图 (a) DNA折纸斑点编码原理; (b) 发送者(Alice)和接收者(Bob)通信流程; (c) 文本“DNA-1954”的编码演示(比例尺: 25 nm) Figure3. Schematic illustration of DNA origami encryption and coding principle: (a) Coding principle of DNA origami spot; (b) the communication procedure between the sender (Alice) and the receiver (Bob); (c) coding demonstration of the text “DNA-1954” (scale bar: 25 nm).
其中m是单个折纸可用的位点数量, $ {P}_{i}^{m} $是m的i种替换可能. 在本研究中, m取值为12, 这导致密钥大小约为32位. 由于骨架链的折叠强烈依赖于通用订书钉链的序列信息, 所以窃密者需要掌握完整的订书钉链序列信息才能重现折纸折叠形状, 使A-DOC具有了很大的密钥空间. 基于骨架链的序列、长度和折叠的难以预测性, 对骨架链或订书钉链进行蛮力攻击实际上是非常困难的. 假设存在聪明的窃密者(命名为Eve), 他可以以某种方式拦截从Alice传递给Bob的骨架链. 实际上, 在交付过程中用伪造品代替DNA的可能性很小. 另一方面, 若想重现折纸折叠形状和上面的图案信息, Eve需要费力地测序, 之后必须破解DNA折纸中骨架的特定路径和滑动, 任何因素的任何变化将导致图案变化. 通过简化模型预测, 对于7249个核苷酸的M13 mp18链, 密钥大小可能达到702位($K_{{\rm{DOE}}}^M = \left\lfloor { {L}/{{10.5}}} \right\rfloor + {\log _2}L$, L为骨架链长度), 而现有高级加密标准(AES)的密钥大小最大仅为256位. 如果使用更长的骨架链(例如p7560和p8064), 理论密钥大小可进一步提升为732和780位. 在以上工作基础上, 进一步提出了多折纸编码单字符的设计, 对字符串长度和可编码字符容量进行了提升, 并以加密唐诗《登鹳雀楼》为例进行演示(图4). 根据汉字代码标准GB2312的规定, 汉字按94个“区”和94个“位”分区索引, 可以看作一个横竖各有94个格子的正方形棋盘, 每个格子对应一个汉字或者符号. 其中1—9区为符号区, 16—87区为汉字编码区, 其他为用户自定义编码区. 如图4(a)所示, 本文使用两个不同标记的十字折纸, 对于第一个折纸, 12个可识别位点中5个黑色点位代表在字符串中的位置信息, 容量为25; 7个蓝色的位点①—⑦编码汉字的区, 称为区码 (section code), 信息容量可达128位(27), 超过了国标规定94位的需求. 同样另一个折纸以相同的五个黑色点位代表位置信息, 对应第一个折纸, 红色的7个点位①—⑦代表在该区所处的位, 称为位码(postion code). 通过两个折纸位置信息匹配读取信息就可得到汉字信息和这个汉字在文本中所处的位置. 在图4(b)中演示了该编码规则的实例, 对于汉字“流”, 根据区码表得到它的区码为33、位码为87, 代表它在区码表中处于33行87列的位置. 然后将区码和位码分别转换为二进制数据, 区码二进制为“0100001”, 位码二进制为“1011101”, 根据红色和蓝色序号的循序依次写入. 同时根据它在诗中的位置定义了它的位置码为15, 即“01110”. 图 4 将汉字在DNA折纸上的加密方案 (a) 区位码在折纸上的编码原理; (b)汉字“流”的编码演示; (c) 28个汉字唐诗文本AFM实验图(比例尺: 40 nm); (d)唐诗随扫描次数收集完成度和错误率图, 正确收集标记为红色, 单个链霉亲和素图案未收集超过20个的标记为白色 Figure4. Scheme of encoding Chinese characters on DNA origami: (a) Encoding principle of section and position code on origami; (b) demonstration of Chinese encoding Chinese character “流” on DNA origami (scale bar: 100 nm); (c) AFM experimental graph of 28 Chinese characters Tang poetry text (scale bar: 40 nm); (d) collection completion and error rate graphs of Tang poetry with the number of scans completed and error rate graphs. The correct collection is marked as red, and the single streptavidin pattern which is not collected for more than 20 will be marked as white.