IP Time to Live (TTL) field used as a covert channel
First Claim
1. A method of determining, in a communications network, an upstream station, among several other candidates, traversed by a packet having a time-to-live (TTL) field arriving at a downstream station, comprising the steps of:
- a) marking the TTL field of the packet flow arriving at the upstream station, in a manner that uniquely identifies the upstream station among all the other concurrently marking upstream stations;
b) receiving and identifying at the downstream station a marked packet flow; and
c) determining, depending upon the TTL field of the marked packet flow received, that said packet flow traversed the upstream station;
wherein the TTL field of the marked packet is identified by looking for constant shifts in statistical parameters and in the distributed TTL value with marking turned on and turned off.
12 Assignments
0 Petitions
Accused Products
Abstract
The Time to Live (TTL) field in an IP header is used as a covert channel in a communication system. More particularly the TTL field can be used to selectively mark packets with unique identifiers as they pass through an upstream station on their way to a downstream station. In this way the source of a traffic flow at least within a particular domain can be absolutely identified. This method of performing a traceback operation doesn'"'"'t utilize additional resources as it relies on functionality which already exists in the system.
51 Citations
11 Claims
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1. A method of determining, in a communications network, an upstream station, among several other candidates, traversed by a packet having a time-to-live (TTL) field arriving at a downstream station, comprising the steps of:
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a) marking the TTL field of the packet flow arriving at the upstream station, in a manner that uniquely identifies the upstream station among all the other concurrently marking upstream stations; b) receiving and identifying at the downstream station a marked packet flow; and c) determining, depending upon the TTL field of the marked packet flow received, that said packet flow traversed the upstream station; wherein the TTL field of the marked packet is identified by looking for constant shifts in statistical parameters and in the distributed TTL value with marking turned on and turned off. - View Dependent Claims (2)
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3. A method of determining, in a communications network, an upstream station, among several other candidates, traversed by a packet having a time-to-live (TTL) field arriving at a downstream station, comprising the steps of:
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a) marking the TTL field of the packet flow arriving at the upstream station in a manner that uniquely identifies the upstream station among all the other concurrently marking upstream stations; and b) receiving and identifying at the downstream station a marked packet flow; and c) determining, depending upon the TTL field of the marked packet flow received, that said packet flow traversed the upstream station; and
comparing the value of the TTL field of packets in a flow to which said packets belong with and without marking being performed, thereby enabling the manner of marking, which identifies the upstream station, to be determined;wherein each upstream marking station is assigned a plurality of values and associated ratios, where the sum of all said associated ratios is 100%; and
the marking station marks a percent of the packet flow given by one of said associated ratios with a corresponding one of said values, thus uniquely identifying its marking.- View Dependent Claims (4, 5)
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6. A system for determining, in a communications network, an upstream station, among several other candidates, traversed by a packet having a time-to-live (TTL) field arriving at a downstream station, comprising:
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a) means for marking the TTL field of the packet flow arriving at the upstream station, in a manner that uniquely identifies the upstream station among all the other concurrently marking upstream stations; and b) means for receiving and identifying at the downstream station a marked packet flow; and c) means for determining depending upon the TTL field of the marked packet flow received that said packet flow traversed the upstream station; wherein the upstream station to mark packets is selected by a group of network edge stations marking concurrently with a common primary mark and one selected station of the group using a secondary unique mark, the selection of the station using the secondary mark rotating among stations of the group. - View Dependent Claims (7, 8, 9, 10, 11)
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Specification