Multi-Valued Physical Unclonable Functions

20年来，半导体制造的水平一直低于100纳米CMOS节点的水平。因此，急剧增加的影响是工艺变化的影响，表现为设备不匹配。然而，也发现不可预测和不可复制的设备不匹配可以用来开发特定类型的电路，用于基于硬件的芯片识别，称为物理不可克隆功能（puf）。puf的主要目的是从这些具有不可预测变化的物理属性生成唯一的密钥或指纹。为了使特定实例在广泛的环境条件下具有稳定的响应，必须应用纠错（信道编码）方法。尽管这种指纹是基于相同设计的组件的非理想制造引起的不匹配，并且这种不匹配遵循统计分布，但是，在今天的绝大多数puf中，读数只是二进制的。然而，对于puf而言，考虑到有限的块长度，这不是规定的或不可避免的，甚至可能不是整个系统的最佳方法。因此，应该考虑多值puf (mpuf)，其中指纹是一个从基数大于2的字母表中提取元素的单词。利用硬件的真实模拟分布并将其映射到多值非二进制响应中，可以提供更多样化和可区分的PUF电路行为，从而产生更大的响应熵。该项目结合了集成电路设计和通信理论的专业知识，目标是利用PUF随机性源的多值特性，增加其读出的熵并生成鲁棒读出。将分析增强信道和源编码的实现努力与增强电路设计措施之间的复杂性权衡。为此，一方面通过集成电路设计与仿真，进行真实的模型建立与模型验证；将选择和优化合适的多值PUF源。另一方面，将设计适应多值特性的信源编码和编码调制方案。这两个部分相互作用强烈：编码部分将为增强的MPUF提供需求和目标度量，这将导致改进的MPUF单元；现实的硬件模型将成为适应的、高性能的编码方案的基础。该项目的结果预计将是一类新的物理不可克隆函数，具有看不见的统计特性和指纹、身份验证或加密密钥生成/密钥存储的可靠性。

Since two decades, the level of semiconductor manufacturing went below the mark of 100 nm CMOS nodes. Thereby, a drastically increasing effect is the influence of process variation manifesting as device mismatch. However, it was also discovered that non-predictable and irreproducible device mismatch can be utilized to develop specific types of circuits for hardware-based chip identification, called Physical Unclonable Functions (PUFs). The main purpose of PUFs is to generate unique keys or fingerprints from these physical properties with non-predictable variations. In order for a specific instance to have a response stable over a wide range of environmental conditions, error correction (channel coding) methods have to be applied.Even though this fingerprint is based on the non-ideal manufacturing-induced mismatch of identically designed components, and this mismatch follows statistical distributions, still, in the vast majority of today's PUFs, the readout is simply binary. However, for the purpose of PUFs and in view of finite block length, this is not prescribed or unavoidable and may even be not the optimum approach w.r.t. the entire system. Thus, multi-valued PUFs (MPUFs) should be considered, where the fingerprint is a word with elements drawn from an alphabet with (finite) cardinality greater than two. Utilizing the true analog distributions of the hardware and mapping it into multi-valued, non-binary responses could provide a more diverse and distinguishable behavior of the PUF circuit yielding a much greater entropy of the response.The proposed project combines the expertise of integrated circuit design and communication theory with the goal to exploit the multi-valued nature of the PUF source of randomness, to increase the entropy of its readout and to generate robust readouts. The complexity tradeoffs between implementation effort of enhanced channel and source coding versus enhanced circuit design measure will be analyzed.To this end, on the one hand, by using integrated circuit design and simulation, realistic model building and model verification is performed. Suited multi-valued PUF sources will be selected and optimized. On the other hand, source coding and coded modulation schemes adapted to themulti-valued nature will be designed. Both parts strongly interact: the coding part will provide requirements and goal metrics for enhanced MPUFs, which will lead to improved MPUF unit cells; the realistic hardware models will be the basis for adapted, highly performing coding schemes.The outcome of the project is expected to be a new class of physical unclonable functions with unseen statistical properties and reliability for fingerprints, authentication or key generation/key storage for cryptography.