Packet flow side channel

1. A system for embedding a covert side channel communication in an overt communication transmitted over a network using a packet stream, comprising:

a. an encoder configured to encode one or more bits of a side channel communication, the encoder including:

i. a packet group selection module configured to select at least two groups of related packets from the overt communication being transmitted on a network, each group of packets including a same number of packets;

ii. a packet relation module configured to relate a packet of one group to a packet of another group to form a pair of packets; and

iii. a packet delay module configured to delay the timing of at least one packet from each pair of packets; and

b. a decoder configured to decode the bits from the side channel communication, the decoder including:

i. an inter-packet delay determination module configured to determine the difference in timing between the two packets for each pair of packets;

ii. a difference determination module configured to determine at least one inter-packet delay difference between two or more determined inter-packet delays; and

iii. a bit extraction module configured to convert the at least one interpacket delay differences into a bit.

2. The system of claim 1 , wherein the encoder uses an encoding algorithm.

3. The system of claim 1 , wherein the decoder uses a decoding algorithm complementary to the encoding algorithm.

4. The system of claim 1 , wherein the encoder and the decoder use a shared secret.

5. The system of claim 1 , wherein the side channel communication includes a watermark.

6. The system of claim 1 , wherein the overt communication includes a VoIP communication.

7. The system of claim 1 , wherein the side channel communication identifies the overt communication.

8. The system of claim 1 , wherein the encoder and the decoder are located on opposite sides of a router.

9. The system of claim 1 , wherein bits are redundantly encoded.

10. A method for embedding a covert side channel communication in an overt communication transmitted over a network using a packet stream, comprising: encoding one or more bits of a side channel communication by:

a. selecting more than one group of related packets from the overt communication being transmitted on a network, each group of packets including a same number of packets, the related packets being consecutive as well as non-consecutive packets;

b. relating a packet of one group to a packet of another group to form a pair of packets; and

c. delaying the timing of at least one packet from each pair of packets.

11. The method of claim 10 , wherein the encoding uses an encoding algorithm.

12. The method of claim 10 , wherein the selecting comprises selecting more than one group of packets in a random manner.

13. The method of claim 10 , wherein the delaying comprises delaying the timing of the at least one packet without buffering the packets.

14. The method of claim 10 , wherein the side channel communication includes a watermark.

15. The method of claim 10 , wherein the overt communication includes a VoIP communication.

16. The method of claim 10 , wherein the side channel communication identifies the overt communication.

17. A method for extracting a covert side channel communication in an overt communication transmitted over a network using a packet stream, comprising: decoding a bit from the side channel communication by:

a. determining inter-packet delays that are the difference in timing between two packets in a pair of packets from the overt communication;

b. determining at least one inter-packet delay difference between two or more determined inter-packet delays; and

c. converting the at least one interpacket delay differences into a bit.

18. The method of claim 17 , wherein the decoding uses a decoding algorithm.

19. The method of claim 17 , wherein the overt communication includes redundantly encoded bits.

20. The method of claim 17 , wherein the side channel communication identifies the overt communication.