System and method for clock-skew-based covert communication
A system and method for clock-skew-based covert communication in which a message formed of message bits is mapped to corresponding symbols having predetermined clock skew values. For each corresponding symbol, an offset value is calculated and added to each timestamp in a predetermined quantity of outgoing TCP segments to generated altered TCP segments, such that an artificial clock skew is induced as measured by a receiver. A clock skew value is determined from each predetermined quantity of TCP segments and mapped to corresponding symbol. The symbols are then mapped to corresponding message bits, and the message is determined from the bits. In this way a message can be sent from a transmitter to a receiver in a way that is covert during transmission and deciphered at the receiver.
1. A system for clock-skew-based covert communication utilizing the Transfer Control Protocol (TCP) comprising:
a transmitter, the transmitter comprising:
a central processing unit (CPU) having a CPU clock which generates a timestamp for outgoing TCP segments, and
an embedding module;
a receiver, the receiver comprising:
a central processing unit (CPU) having a CPU clock which generates a timestamp for incoming TCP segments, and
an extractor module; and
a network communicatively coupling the transmitter and the receiver;
wherein the embedding module:
obtains a message to be sent, the message including message bits;
maps the message bits to a corresponding symbol, the symbol having an associated clock skew value;
calculates an offset value to be added to each timestamp in a predetermined quantity of TCP segments to result in the associated clock skew value for the symbol;
adds the calculated offset value to each timestamp in the predetermined quantity of TCP segments to generate a predetermined quantity of altered TCP segments; and
transmits the predetermined quantity of altered TCP segments to the network; and,
wherein the extractor module:
receives the predetermined quantity of altered TCP segments;
determines the clock skew value from the timestamps of the predetermined quantity of altered TCP segments;
determines the symbol that corresponds to the clock skew value based on predetermined threshold levels;
extracts the symbol through analog to digital conversion (A/D);
maps the symbol to the corresponding message bits; and,
obtains the message from the message bits.
2. A method for clock-skew-based covert communication utilizing the Transfer Control Protocol (TCP) comprising:
establishing a TCP session between a transmitter and a receiver over a communication network;
establishing a baseline clock skew of the transmitter by the receiver;
obtaining a message to be sent by the transmitter, the message including message bits;
mapping the message bits to a corresponding symbol, the symbol having an associated clock skew value;
calculating an offset value to be added to each timestamp in a predetermined quantity of TCP segments to result in the associated clock skew value for the symbol;
adding the calculated offset value to each timestamp in the predetermined quantity of TCP segments to generate a predetermined quantity of altered TCP segments;
transmitting the predetermined quantity of altered TCP segments over the communication network to the receiver;
receiving the predetermined quantity of altered TCP segments at the receiver;
determining the associated clock skew value from the timestamps of the predetermined quantity of altered TCP segments;
determining the corresponding symbol for the clock skew based on predetermined threshold levels;
extracting the symbol through analog to digital conversion (A/D);
mapping the symbol to corresponding message bits; and,
obtaining the message from the message bits.
3. A method for embedding a clock-skew-based covert communication at a transmitter utilizing the Transfer Control Protocol (TCP) comprising:
obtaining a message to be sent by the transmitter, the message including message bits;
mapping the message bits to a corresponding symbol, the symbol having an associated clock skew value;
calculating an offset value to be added to each timestamp in a predetermined quantity of TCP segments to result in the associated clock skew value for the symbol;
adding the calculated offset value to each timestamp in the predetermined quantity of TCP segments to generate a predetermined quantity of altered TCP segments;
transmitting the predetermined quantity of altered TCP segments.
4. A method for extracting a clock-skew-based covert communication utilizing the Transfer Control Protocol (TCP) comprising:
receiving a predetermined quantity of altered TCP segments, the altered TCP segments having an offset value added to each timestamp in the predetermined quantity of altered TCP segments;
determining a clock skew value from the timestamps of the predetermined quantity of altered TCP segments;
determining a symbol that corresponds to the clock skew value based on predetermined threshold levels;
extracting the symbol through analog to digital conversion (A/D);
mapping the symbol to associated message bits; and,
obtaining the message from the message bits.