title: Building trustworthy smart contracts using interactive theorem proving

authors: Britten, Daniel

subjects: formal methods

abstract: There are varying approaches to the verification of smart contracts using formal methods. This thesis advocates for the use of high-level specifications coupled with a verified compiler to low-level bytecode, such as for the Ethereum Virtual Machine. Taking this approach allows for specifications to more closely match natural language, while ensuring that the specifications apply to the real bytecode executed on-chain.

Interactive theorem proving can provide the foundation for developing provably correct smart contracts. Due to the immutable nature of smart contracts and their potential to manage highly valuable assets and tokens representing power, techniques to ensure their correctness are of paramount importance.

This thesis extends the DeepSEA (Deep Simulation of Executable Abstractions) smart contract language targeting the Ethereum Virtual Machine by mitigating the issues associated with reentrancy and introducing a model of relevant aspects of a blockchain. This enables the specification and verification of two case studies which exemplify the approach of developing provably correct smart contracts.

The specifications for the case studies are written in the language of the Coq Proof Assistant, making arbitrary mathematical statements expressible. The blockchain model enables stating and proving temporal properties relating to the execution of smart contract over time.

While smart contracts are an ideal application area for formal methods in general and interactive theorem proving in particular, the techniques exemplified in this thesis could be applied throughout software engineering. The relatively young age of smart contract languages and typically small size of smart contract programs makes the application of interactive theorem proving more tractable. Future work could involve demonstrating the applicability to many interrelated smart contracts and to larger software projects in different domains.

The first three chapters of this thesis cover introductory and background material. This is followed by the contributions to the DeepSEA system. The two case studies and the proof themes arising from them are then presented. Finally, concluding remarks and future work are discussed.

text: Building trustworthy smart contracts using interactive theorem proving There are varying approaches to the verification of smart contracts using formal methods. This thesis advocates for the use of high-level specifications coupled with a verified compiler to low-level bytecode, such as for the Ethereum Virtual Machine. Taking this approach allows for specifications to more closely match natural language, while ensuring that the specifications apply to the real bytecode executed on-chain.

Interactive theorem proving can provide the foundation for developing provably correct smart contracts. Due to the immutable nature of smart contracts and their potential to manage highly valuable assets and tokens representing power, techniques to ensure their correctness are of paramount importance.

This thesis extends the DeepSEA (Deep Simulation of Executable Abstractions) smart contract language targeting the Ethereum Virtual Machine by mitigating the issues associated with reentrancy and introducing a model of relevant aspects of a blockchain. This enables the specification and verification of two case studies which exemplify the approach of developing provably correct smart contracts.

The specifications for the case studies are written in the language of the Coq Proof Assistant, making arbitrary mathematical statements expressible. The blockchain model enables stating and proving temporal properties relating to the execution of smart contract over time.

While smart contracts are an ideal application area for formal methods in general and interactive theorem proving in particular, the techniques exemplified in this thesis could be applied throughout software engineering. The relatively young age of smart contract languages and typically small size of smart contract programs makes the application of interactive theorem proving more tractable. Future work could involve demonstrating the applicability to many interrelated smart contracts and to larger software projects in different domains.

The first three chapters of this thesis cover introductory and background material. This is followed by the contributions to the DeepSEA system. The two case studies and the proof themes arising from them are then presented. Finally, concluding remarks and future work are discussed.

year: 2024

title: High temperature deformation behavior of Ti–46Al–2Cr–4Nb–0.2Y alloy

authors: Kong, Fantao

subjects: Deformation

abstract: The hot deformation characteristics of cast and hot isostatically pressed Ti-46Al-2Cr-4Nb-0.2Y (at%) alloy in the temperature range of 1100-1250°C and strain rate range of 0.01-1.0s -1 using hot compression tests were studied. The processing map of the alloy at true strain of 0.5 was also developed on the basis of the dynamic materials model (DMM). The experimental results show that the flow stress decreases significantly with increasing deformation temperature and decreasing strain rate. Using the kinetic rate equation the stress exponent n and the apparent activation energy of deformation Q were determined as 4.47 and 400.4kJmol -1, respectively. The efficiency values of power dissipation of the domain at strain rate below 0.4s -1 show that the dynamic recrystallization occurring of γ phase in the alloy is easier in the wide deformation temperature range (1100-1250°C) due to low stacking fault energy. The fraction of new recrystallized grains increased with increasing the hot deformation temperature at a given strain rate. With the increasing of strain rate, the uniformity of microstructure was decreased. The domain defined by the temperature range of 1200-1230°C and the strain rate range of 0.01-0.05s -1 which corresponds to a peak efficiency of about 60% is the optimal deformation condition of the alloy. Based on the optimal deformation conditions, a cylindrical sample was near isothermally forged. The microstructure and shape of pancake by forging was in good agreement with the prediction of processing map.

text: High temperature deformation behavior of Ti–46Al–2Cr–4Nb–0.2Y alloy The hot deformation characteristics of cast and hot isostatically pressed Ti-46Al-2Cr-4Nb-0.2Y (at%) alloy in the temperature range of 1100-1250°C and strain rate range of 0.01-1.0s -1 using hot compression tests were studied. The processing map of the alloy at true strain of 0.5 was also developed on the basis of the dynamic materials model (DMM). The experimental results show that the flow stress decreases significantly with increasing deformation temperature and decreasing strain rate. Using the kinetic rate equation the stress exponent n and the apparent activation energy of deformation Q were determined as 4.47 and 400.4kJmol -1, respectively. The efficiency values of power dissipation of the domain at strain rate below 0.4s -1 show that the dynamic recrystallization occurring of γ phase in the alloy is easier in the wide deformation temperature range (1100-1250°C) due to low stacking fault energy. The fraction of new recrystallized grains increased with increasing the hot deformation temperature at a given strain rate. With the increasing of strain rate, the uniformity of microstructure was decreased. The domain defined by the temperature range of 1200-1230°C and the strain rate range of 0.01-0.05s -1 which corresponds to a peak efficiency of about 60% is the optimal deformation condition of the alloy. Based on the optimal deformation conditions, a cylindrical sample was near isothermally forged. The microstructure and shape of pancake by forging was in good agreement with the prediction of processing map.

year: 2012

title: Mokena Hou and his wife Rina

authors: Hart, Philip

abstract: Mokena Hou had a distinguished whakapapa, but as nephew to Hou was subordinate to the latter’s son, Karauna Hou. He was born near the Te Aroha hot pools, and his future wife, Rina, who also had illustrious ancestors, including some Ngati Haua, was born in the same area. Both were affiliated to several hapu. After the Hauraki tribes fled from Ngapuhi in 1821, he would be present at the battle of Taumatawiwi in 1830 (though he did not fight) and participated in a later siege of the Ngati Haua pa at Matamata. During the 1830s and later, he mostly cultivated land and dug gum in the lower Waihou region and as well as cultivating at Te Aroha. 
 After living at Kaitawa before the Thames goldfield opened, nearby, in 1867, he moved to Te Aroha, where he would live continuously, warding off the ambitions of Ngati Haua. When the land court investigated the ownership of blocks of land in Hauraki, he sought to obtain as many interests as possible, not always successfully, and tried to get more than his fair share of both land and revenue. 
A devoted Anglican, he assisted the early missionaries to the Waihou region. Wanting peaceful relations with Pakeha, he assisted both the surveying and the settlement of the Aroha Block. When gold was discovered at Te Aroha in 1880, he assisted the prospectors, opened his land for mining and for a township, and invested in some claims, expecting and obtaining a good financial reward. He may have assisted in making the hot pools a public reserve, and certainly gave sections of land within the settlement for public and religious purposes. When he and his wife died a month apart, they were fondly remembered.

text: Mokena Hou and his wife Rina Mokena Hou had a distinguished whakapapa, but as nephew to Hou was subordinate to the latter’s son, Karauna Hou. He was born near the Te Aroha hot pools, and his future wife, Rina, who also had illustrious ancestors, including some Ngati Haua, was born in the same area. Both were affiliated to several hapu. After the Hauraki tribes fled from Ngapuhi in 1821, he would be present at the battle of Taumatawiwi in 1830 (though he did not fight) and participated in a later siege of the Ngati Haua pa at Matamata. During the 1830s and later, he mostly cultivated land and dug gum in the lower Waihou region and as well as cultivating at Te Aroha. 
 After living at Kaitawa before the Thames goldfield opened, nearby, in 1867, he moved to Te Aroha, where he would live continuously, warding off the ambitions of Ngati Haua. When the land court investigated the ownership of blocks of land in Hauraki, he sought to obtain as many interests as possible, not always successfully, and tried to get more than his fair share of both land and revenue. 
A devoted Anglican, he assisted the early missionaries to the Waihou region. Wanting peaceful relations with Pakeha, he assisted both the surveying and the settlement of the Aroha Block. When gold was discovered at Te Aroha in 1880, he assisted the prospectors, opened his land for mining and for a township, and invested in some claims, expecting and obtaining a good financial reward. He may have assisted in making the hot pools a public reserve, and certainly gave sections of land within the settlement for public and religious purposes. When he and his wife died a month apart, they were fondly remembered.

year: 2016