On the Logical Independence of (DR) and (CLA)

In 1941, J.H.C. Whitehead posed the question of whether asphericity is a hereditary property for 2-dimensional CW complexes. This question remains unanswered, but has led to the development of several algebraic and topological properties that are sufficient (but not necessary) for the asphericity of presentation 2-complexes. While many of the logical relationships between these flavors of asphericity are known, there remain a few to be answered. In particular, it has long been known that Cohen-Lyndon aspherical (CLA) complexes are not necessarily diagrammatically reducible (DR), but the existence of a (DR) complex which is not (CLA) remains open. We resolve this by showing that the presentation 2-complex associated to the presentation is (DR) but not (CLA). In fact, we prove that if a nontrivial group G occurs as the fundamental group of a (DR) 2-complex, then there is a (DR) 2-complex with fundamental group $G$ that is not (CLA)

The Apple Sandbox

Despite the never ending proclamations of the end of memory corruption vulnerabilities, modern software continues to fall to exploits taking advantage of these bugs. Current operating systems incorporate a battery of exploit mitigations [4][10][3] making life significantly more complex for attackers turning these bugs into attacks. Additionally, developer

BGP-Inspect - Extracting Information from Raw BGP Data

Abstract — While BGP routing datasets, consisting of raw routing data, are freely available and easy to obtain, extracting any useful information is tedious. Currently, researcher and network operators implement their own custom data processing tools and scripts. A single tool that provides easy access to the information within large raw BGP data-sets could be used by both communities to avoid re-writing these tools each time. Moreover, providing not just raw BGP messages, but some commonly used summary statistics as well can help guide deeper custom analyses. Based on these observations this paper describes the first steps towards building a scalable tool. We describe the various techniques and algorithms we have used to build an efficient generic tool called BGP-Inspect. When dealing with large datasets, dataset size, lookup speed, and data processing time are the most challenging issues. We describe our implementations of chunked compressed files and B+ tree indices that attempt to address these issues. We then provide an evaluation of our implementations. Finally, we provide some example scenarios and case studies where BGP-Inspect can provide useful insight into the management and operation of complex BGP based networks. An efficient and flexible back-end custom BGP message database, coupled with an intuitive and easy to use web-based query front-end makes BGP-Inspect a unique and powerful tool. I

BGP-Inspect - Extracting Information from Raw BGP Data

Abstract — While BGP routing datasets, consisting of raw routing data, are freely available and easy to obtain, extracting any useful information is tedious. Currently, researcher and network operators implement their own custom data processing tools and scripts. A single tool that provides easy access to the information within large raw BGP data-sets could be used by both communities to avoid re-writing these tools each time. Moreover, providing not just raw BGP messages, but some commonly used summary statistics as well can help guide deeper custom analyses. Based on these observations this paper describes the first steps towards building a scalable tool. We describe the various techniques and algorithms we have used to build an efficient generic tool called BGP-Inspect. When dealing with large datasets, dataset size, lookup speed, and data processing time are the most challenging issues. We describe our implementations of chunked compressed files and B+ tree indices that attempt to address these issues. We then provide an evaluation of our implementations. Finally, we provide some example scenarios and case studies where BGP-Inspect can provide useful insight into the management and operation of complex BGP based networks. An efficient and flexible back-end custom BGP message database, coupled with an intuitive and easy to use web-based query front-end makes BGP-Inspect a unique and powerful tool. I