Divakar Yadav

Formal development of byzantine immune total order broadcast system using event-b

A reliable broadcast eventually delivers messages to all participating sites. A total order broadcast is a stronger notion of a reliable broadcast that deliver messages to all processes in a same delivery order. A formal rigorous reasoning is required to precisely understand behaviour of such techniques and an assurance is required to understand how they achieve the objectives. Event-B is a formal technique used for specifying and reasoning about complex systems. In this technique, a system is developed incrementally by adding more details in refinement to obtain more concrete specifications. In this paper, we present a formal development of Byzantine immune total order broadcast system using Event-B. We outline an abstract model specifying total order broadcast using fixed sequencer and introduce more details at refinement level for moving sequencer and detection of Byzantine sequencer.

Verification of Money Atomicity in Digital Cash Based Payment System

Digital cash, analogous to the paper cash, is a certificate that carries a value. It is issued by an authorized entity and is verifiable by all. It can be used as an instrument for making payments or purchases. Unlike paper cash, being a digital data, it may be easily replicated which gives a scope for duplicate spending of the cash certificates. Digital cash based payment systems can be classified as business critical systems as any failure may lead to loss of trust. Verification of critical requirements of such systems is therefore essential. In this paper, we present refinement approach for construction of the models of the digital cash based payment system using Event-B, wherein we verify how money atomicity property can be preserved in these systems. This ensures that money is neither generated nor destroyed in the electronic payment transactions.

Analyzing data flow in trustworthy electronic payment systems using event-b

Modern days scientific and commercial applications are fairly large and complex and its reliance on large-scale communication, distributed computing infrastructure and complex software system is growing. Electronic payment systems are at the core of many such financially critical software systems. Any failure in such applications may end up in financial losses and loss of trust of users. It is required that these systems exhibit trustworthy behavior and must be able to tolerate failures or attacks. Trustworthiness is now being addressed as an important issue in development of future software systems. In this paper we outline application of formal methods to ensure trustworthiness of electronic payment systems. B specifications of DigiCash payment system are presented. We have used ProB Model checker and animator for temporal model check and constraint based checking, discover errors due to invariant violation and deadlocks, thereby, validating the specifications.

Formal verification of security protocol with B method

Security Protocols are fundamental building block of many important applications. These protocols are used to achieve various security requirements such as confidentially, authentication, integrity etc. of the applications. These protocols must be tested for their functional correctness before they are used. In many of the protocol errors have been detected, in spite of investing lot of time in their design. Modified Needham Schroeder Symmetric Key Protocol is a security protocol that incorporates an exchange of messages between two or more agents, for establishing a cryptographic key, and authenticating the identities of the agents. Authentication protocol has to be designed in such a way that makes it robust against replay attacks by any intruder. In this paper, use of formal methods for verification of correction of modified Needham-Schroeder Symmetric Key Protocol is demonstrated. B method has been used for developing specification of modified Needham-Schroeder Symmetric Key protocol and thereafter specifications are model checked using proB model checker. The specifications are free from deadlock and satisfy the behaviour or properties of the system expressed as invariants. It is verified that specifications leaves no spaces for the replay attack.

Analysis of Database Replication Algorithm in Local and Global Networks

this paper, a database replication algorithm is presented. The main idea is to reduce the latency in database replication while maintaining very high throughput. The main points of the algorithm are detailed in this paper. Simulation results are presented to evaluate throughput and average delay. For the in-depth analysis of the algorithm, various cases are considered and it has been found that if the numbers of servers that can serve requests are larger in number then throughput is very high with very less average delay. The overall, throughput and average delay also depend heavily on the load and if load is comparatively less (< 0.8) then the throughput is very high and average delay is nearly zero.

Rigorous Design of Lazy Replication System Using Event-B

Eager replication is a technique of replication that ensures high consistency. Unfortunately, it degrades the system performance by increasing the response time and sacrificing availability. Lazy replication is a technique that provides high availability and ensures that database will eventually be in a consistent state. A formal rigorous reasoning is required to precisely understand the behavior of such techniques and to understand how they achieve the objectives. Event-B is a formal technique that is used for specifying and reasoning about complex systems. In this paper, we present a formal development of lazy replication system using Event-B. We outline our model for distributed environment where same database is replicated at all the sites. After updating the database locally within transactional framework messages are broadcast to other sites so that they can change their replicas.

Rigorous Design of Partition-Aware Total Order Broadcast System using Event-B

In distributed system, the sites communicate with each other by exchange of messages. A total order broadcast is a reliable broadcast that ensures delivery of messages to the sites in the same order. For the fault tolerant applications, ordering algorithm must support the network partitions and site failure. In this paper, we present a formal model of total order broadcast system in the presence of network partition and site failures. We have used Event-B as a formal technique for the development of our model. In this technique system is built in several stages by gradually introducing the details in the refinement steps. We outline an abstract model specifying total order broadcast and introducing the details in the refinement level for considering the case of network partitioning and site failure. General Terms Group communication primitives, B method, network partition.