Ptacek and Newsham [14] showed how to evade signature detection at Intrusion Prevention Systems (IPS) using TCP and IP Fragmentation. These attacks are implemented in tools like FragRoute, and are institutionalized in IPS product tests. The classic defense is for the IPS to reassemble TCP and IP packets,and to consistently normalize the output stream. Current IPS standards require keeping state for 1 million connections. Both the state and processing requirements of reassembly and normalization are barriers to scalability for an IPS at speeds higher than 10 Gbps.In this paper, we suggest breaking with this paradigm using an approach we call Split-Detect. We focus on the simplest form of signature, an exact string match, and start by splitting the signature into pieces. By doing so the attacker is either forced to include at least one piece completely in a packet, or to display potentially abnormal behavior (e.g., several small TCP fragments or out-of-order packets) that cause the attacker's flow to be diverted to a slow path. We prove that under certain assumptions this scheme can detect all byte-string evasions. We also show using real traces that the processing and storage requirements of this scheme can be 10% of that required by a conventional IPS, allowing reasonable cost implementations at 20 Gbps. While the changes required by Split-Detect may be a barrier to adoption, this paper exposes the assumptions that must be changed to avoid normalization and reassembly in the fast path.
This report describes the design and implementation of a gigabit ATM switching system supporting link rates from 150 Mb/s to 2.4 Gb/s, with a uniquely e cient multicast switch a r c hitecture that enables the construction of systems with essentially constant per port costs for con gurations ranging from 8 to 4096 ports and system capacities approaching 10 Tb/s. The system design supports many-to-one and many-to-many forms of multicast, in addition to the usual one-to-many. It also provides multicast virtual paths, constant time con guration of multicast connections and an e cient p a c ket-level discard method, that can achieve 100% link e ciencies, without large bu ers.
Ptacek and Newsham [14] showed how to evade signature detection at Intrusion Prevention Systems (IPS) using TCP and IP Fragmentation. These attacks are implemented in tools like FragRoute, and are institutionalized in IPS product tests. The classic defense is for the IPS to reassemble TCP and IP packets, and to consistently normalize the output stream. Current IPS standards require keeping state for 1 million connections. Both the state and processing requirements of reassembly and normalization are barriers to scalability for an IPS at speeds higher than 10 Gbps.In this paper, we suggest breaking with this paradigm using an approach we call Split-Detect. We focus on the simplest form of signature, an exact string match, and start by splitting the signature into pieces. By doing so the attacker is either forced to include at least one piece completely in a packet, or to display potentially abnormal behavior (e.g., several small TCP fragments or out-of-order packets) that cause the attacker's flow to be diverted to a slow path. We prove that under certain assumptions this scheme can detect all byte-string evasions. We also show using real traces that the processing and storage requirements of this scheme can be 10% of that required by a conventional IPS, allowing reasonable cost implementations at 20 Gbps. While the changes required by Split-Detect may be a barrier to adoption, this paper exposes the assumptions that must be changed to avoid normalization and reassembly in the fast path.
Since commercially available formant trackers are often inconsistent, much hand-editing is required to correct their outputs. A software package is currently being developed that may reduce this problem. Two female and two male speakers were recorded producing ten vowels in S-vowel-T context, each vowel twice. Boundaries between burst-friction, glottal-source, and silent segments are located using zero crossing and rms energy measurements. Pitch and formant-frequency values are extracted using the API and SGM commands of ILS. Our software corrects the pitch contour and calculates a sensory reference from it [J. D. Miller, J. Acoust. Soc. Am. 85, 2114–2134 (1989)]. Rules based on the relation between peak frequencies and this sensory reference are utilized to label the peaks as formants and the resulting formant tracks are then low-pass filtered. In this way, satisfactory tracking is obtained for all 80 syllables. [Work supported by AFOSR and NIDCD.]
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.