COVERT CHANNELS A covert channel is a communication channel based on the use of system resources not normally intended for communication between the subjects processes in the system COVERT CHANNELS ID: 728522
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COVERT CHANNELSRavi SandhuSlide2
COVERT CHANNELSA covert channel is a communication channel based on the use of system resources not normally intended for communication between the subjects (processes) in the systemSlide3
COVERT CHANNELSLow User
High Trojan Horse
Infected Subject
High
User
Low Trojan Horse
Infected Subject
COVERT
CHANNEL
Information is leaked unknown to the high
userSlide4
COVERT CHANNELS
The concern is with subjects not users
users are trusted (must be trusted) not to disclose secret information outside of the computer system
subjects are not trusted because they may have Trojan Horses embedded in the code they execute
star-property prevents overt leakage of information and does not address the covert channel problemSlide5
RESOURCE EXHAUSTION CHANNEL(STORAGE CHANNELS)
Given
5GB
pool of dynamically allocated memory
HIGH PROCESS
bit = 1
Þ
request 5GB of memory
bit = 0 Þ request 0GB of memoryLOW PROCESS
request 5GB of memory if allocated then bit = 0 otherwise bit = 1Slide6
LOAD SENSING CHANNEL(TIMING CHANNEL)
HIGH PROCESS
bit = 1
Þ
enter computation intensive loop
bit = 0
Þ
go to sleepLOW PROCESS
perform a task with known computational requirements if completed quickly then bit = 0 otherwise bit = 1Slide7
COPING WITH COVERT CHANNELSidentification
close the channel or slow it down
detect attempts to use the channel
tolerate its existenceSlide8
SIDE CHANNELS VS COVERT CHANNELS
Covert channels require a cooperating sender and receiver
Side channels do not require a sender but nevertheless information is leaked