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**1 - 2**of**2**### Black-Box, Round-Efficient Secure Computation via Non-Malleability Amplification

"... We present round-efficient protocols for secure multi-party computation with a dishonest majority that rely on black-box access to the underlying primitives. Our main contributions are: a O(log ∗ n)-round protocol that relies on black-box access to dense cryptosystems, homomorphic encryption schemes ..."

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We present round-efficient protocols for secure multi-party computation with a dishonest majority that rely on black-box access to the underlying primitives. Our main contributions are: a O(log ∗ n)-round protocol that relies on black-box access to dense cryptosystems, homomorphic encryption schemes, or lossy encryption schemes. This improves upon the recent O(1) log ∗ n-round protocol of Lin, Pass and Venkitasubramaniam (STOC 2009) that relies on non-black-box access to a smaller class of primitives. a O(1)-round protocol requiring in addition, black-box access to a one-way function with sub-exponential hardness, improving upon the recent work of Pass and Wee (Eurocrypt 2010). These are the first black-box constructions for secure computation with sublinear round complexity. Our constructions build on and improve upon the work of Lin and Pass (STOC 2009) on non-malleability amplification, as well as that of Ishai et al. (STOC 2006) on black-box secure computation. In addition to the results on secure computation, we also obtain a simple construction of a O(log ∗ n)-round non-malleable commitment scheme based on one-way functions, improving upon the recent O(1) log ∗ n-round protocol of Lin and Pass (STOC 2009). Our construction uses a novel transformation for handling arbitrary man-in-the-middle scheduling strategies which improves upon a previous construction of Barak (FOCS 2002). Keywords- secure multi-party computation, round complexity, blackbox constructions, non-malleable commitments. 1.

### Web Service Authentication and Multilevel Security

"... Objective: The objective of the work is the implementation of trusted system in network security. The problem has been identified as minimizing the time and space complexity while adding the vertices and edges in the implementation of zero knowledge protocol using Graph Isomorphism, the identificati ..."

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Objective: The objective of the work is the implementation of trusted system in network security. The problem has been identified as minimizing the time and space complexity while adding the vertices and edges in the implementation of zero knowledge protocol using Graph Isomorphism, the identification of the classes of the graph and the distribution of the isomorphic graphs as the private keys in public key cryptosystems for authentication. Methods: Guillou-Quisquarter algorithm is used as basic zero knowledge protocol. An adjacency matrix is generated by reordering the vertices and communicated for authentication. Constructed the isomorphic graph using the nauty algorithm and classify this to each set of users. Nauty algorithm is used to check for the isomorphism of graphs which uses the canonical method using partitions and search tree. Implemented the partition algorithm and generated the search tree. Three graphs are generated as sample data. We have used the toy example of Bank Loan to implement the new method. Findings: The improvised algorithm minimizes the time and space complexity. We have increased the vertices and proved that the time complex-ity won’t increase with the increase in the number of vertices. We have identified the classes of graph for each set of users for authentication. This graph is given as the key in public key cryptosystems for the implementation of trusted system. Isomorphic graph is generated as the key for each set of users to implement the multilevel security. Thus the authentication and the multilevel security aspects have been handled by the use of class of isomorphic graphs and Guillou