# Patent

## Title
Method for encryption obfuscation

## Abstract

A system and method provide a signal carrier; an overt persistent digital channel containing a host signal and carried on the signal carrier; a non-persistent channel encoded onto the host signal by timing variation of the host signal, the non-persistent channel including access data for accessing hidden information in the host signal.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims priority from U.S. Provisional Patent Application Ser. No. 61/988,409, filed May 5, 2014, U.S. Provisional Patent Application Ser. No. 61/988,416, filed May 5, 2014, U.S. Provisional Patent Application Ser. No. 61/988,423, filed May 5, 2014, and U.S. Provisional Patent Application Ser. No. 61/988,418, filed May 5, 2014, all of which are incorporated herein by reference in their entirety.


FIELD OF THE INVENTION
The present invention generally relates to secure communications, and in particular to such communications which vary the timing of communication signals.
BACKGROUND OF THE INVENTION
Often times, when U.S. Diplomats are working outside the continental United States (OCONUS), communications are closely monitored by the visited country. The monitoring is done to identify transmissions that are considered harmful to local governments. When United States personal are operating in these countries, they need to send their information back to the US using encryption to protect their mission. There are, of course, other instances where securely transmitted communications are very useful. The sending of encrypted messages either over-the-air or over a terrestrial link can bring undesired attention to the sender, which could have damaging consequences. Therefore it is useful to have a method for sending secure communications that do not appear to be secure.
SUMMARY OF THE INVENTION
One embodiment of the present invention provides a system for encoding data in a signal, comprising: at least one signal carrier; an overt persistent digital channel containing a host signal and carried on the at least one signal carrier; a non-persistent channel encoded onto the host signal by timing variation of the host signal, the non-persistent channel including access data for accessing hidden information in the host signal. The term “non-persistent” means that without specific knowledge as to how to receive and process the channel, the data in the non-persistent channel is lost.
The access data may be selected from the group consisting of a stencil, a code book and a decryption key. The host signal may be an intelligible work of nominal information. The host signal may be encrypted and the access data may be an encryption key. The encrypted host signal may be encoded with a code book to reduce entropy, prior to encoding the host signal with the non-persistent channel. The timing variation may be less than a level of timing stability for detecting and capturing the data stream.
The system may further comprise: a processor coupled to receive the host signal from the at least one signal carrier; and a high stability oscillator (HSO) producing a reference signal coupled to the processor for use in reading pulse timing variations of the host signal, wherein the reference signal has a stability greater than the level of timing variations of the host signal; wherein the timing variations of the host signal are smaller than the sampling period for detecting and capturing the data stream. The host signal may be a digital data stream, and the timing variations may be pulse timing variations.
Another embodiment of the present invention provides a method for sending data on a signal carrier, comprising: modulating a host signal in an overt persistent channel to create a non-persistent channel including access data, using timing variations, wherein the access data provides means for accessing hidden data in the host signal; reading timing variations from the host signal for separating the access data; and accessing the hidden data using the access data.
The access data may be selected from the group consisting of a stencil, a code book and a decryption key. The host signal may be an intelligible work of nominal information.
The host signal may be encrypted and the access data is an encryption key. The method may further comprise encoding the host signal with a code book to reduce entropy, prior to encoding the host signal with the non-persistent channel.
The pulse timing variation may be smaller than the sampling period for detecting and capturing the host signal. The host signal may be a digital data stream, and the timing variations may be pulse timing variations. The host signal may be an analog signal.



BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is illustratively shown and described in reference to the accompanying drawings, in which:
FIG. 1 illustrates a steganographic method in accordance with an embodiment of the present invention.
FIG. 2 illustrates a general method for message encoding and decoding in accordance the embodiment of FIG. 1.
FIG. 3 illustrates a method for message encoding using a code book in accordance with another embodiment of the present invention.
FIG. 4 illustrates a method for message encrypting and encoding in accordance with yet another embodiment of the present invention.



DETAILED DESCRIPTION OF THE DRAWINGS
This application describes three methods for sending secure messages. In the methods described, two channels are used to send the message. The first channel is an overt channel, which carries a message that is openly detectable. The second channel is a non-persistent channel, which includes data or keys for accessing information hidden in the open channel. The term “non-persistent” means that without specific knowledge as to how to receive and process the channel, the data in the non-persistent channel is lost. To create the non-persistent channel, an overt channel is generated with minimal timing jitter as limited by a high stability oscillator (HSO) and other system constraints. Non-persistent data is then encoded onto the nominally jitter-free overt channel by precisely modulating the signal timing. The reference signal has a stability of 10−15 part of a second as opposed to the de facto industry standard of Cesium, which is 10−12. An example of implementing a non-persistent channel is described in copending U.S. Patent Application for METHOD AND SYSTEM FOR NON-PERSISTENT COMMUNICATION, filed on the same day herewith, and hereby incorporated herein in its entirety.
Using a modulation scheme such as a Gaussian Clock Dither Modulation scheme and the HSO, the data in the non-persistent channel is imperceptible to anyone not possessing a comparable oscillator tuned to the appropriate frequency. The keys are extracted as they are received and applied directly to the cipher text message, and then the keys are discarded once used. The message and the keys are transmitted and processed in a streaming fashion.
Anyone intercepting these transmissions, not using an HSO with comparable stability, will lose the non-persistent channel, upon reception. This is because the granularity of the received transmission will have insufficient time resolution to detect the non-persistent channel.
The first method 10 is a steganographic approach, which is illustrated in FIG. 1. An overt channel 12 transmits a host message 14. Host message 14 can be any suitable form of digital message, a newspaper article, or other literature or data.
Host message 14 is also provided to a digital stencil module 16. Digital stencil module 16 accepts both the message 18 to be securely transmitted and the host message 14 as inputs, and it outputs a digital stencil 20 identifying the secure message 18 in the host message 14. Digital stencil 20 is a virtual overlay used to identify either the characters, in the case of an ASCII host message 14, or the bits, in the case of a digital host message 14, to be used to decode the host message and reconstruct the actual message 18 that was transmitted. Stencil 20 is then used in a timing modulator 22 to modulate the timing of pulses in host message 14 to form non-persistent channel 13 and thereby transmit the stencil 20. This nominal encoding 10 and decoding 11 is graphically illustrated in FIG. 2. Whereas encoding 10 involves comparing a host message 14 to the message 18 to be sent to produce stencil 20, decoding 11 involves comparing host message 14 to stencil 20 to provide the message 18.
The ability of this embodiment to send the digital stencil along with the message on the non-persistent channel because the stencil is virtually imperceptible reduces risk that a stencil might be intercepted or otherwise compromised. Additionally, the message does not appear to be encrypted because the host message simply appears to be a nominal text.
FIG. 3 illustrates an encoding method 24 which uses a code hook. Again, an overt channel 26 is used for sending a host message 14 and also for carrying a non-persistent channel 28. Host message 14 is simply encoded with a message 18 to be sent in step 30 using a codebook 32. Codebook 32 is transmitted via the non-persistent channel 28 by encoding it onto the encoded message 34 in overt channel 26.
Again, the ability to send the code book along with the message on the non-persistent channel reduces the risk of discovery of the codebook because the code book is virtually imperceptible for the reasons described above. Additionally, the message does not appear to be encrypted.
FIG. 4 illustrates a hybrid method 40 using both encryption and encoding. The message 18 is first encrypted in step 42 using one or more encryption keys 44. The encrypted message 46 is then encoded using a codebook in step 48. This encoding reduces entropy, which is a tell-tale sign of encryption. The one or more encryption keys 44 are provided over the non-persistent channel 50 which is encoded by timing variations onto overt channel 52. For this implementation the code book must be known by both the sender and the receiver.
The implementation of FIG. 4 sends the encryption keys along with the message on the non-persistent channel, and that the encryption keys are virtually imperceptible for the reasons described above. Encryption keys 44 are also readily changeable. Additionally, the message does not appear to be encrypted.
The present invention is introduced using examples and particular embodiments for descriptive purposes. Although a variety of examples are presented to show how various configurations can be employed to achieve the desired improvements, these particular embodiments are only illustrative and not intended in any way to restrict the inventions presented.
The present application, METHOD OF ENCRYPTION OBFUSCATION is being filed on the same day as and in conjunction with related applications: METHOD FOR DETECTING TIME DELAYS IN NON-PERIODIC SIGNALS; METHOD AND SYSTEM FOR NON-PERSISTENT COMMUNICATION; and METHOD AND SYSTEM FOR NON-PERSISTENT REAL-TIME ENCRYPTION KEY DISTRIBUTION, which applications all share some common inventors herewith, and the contents of which are al hereby incorporated herein in their entirety.

## Claims

1. A system for encoding data in a signal, comprising:
a hardware oscillator to provide at least one signal carrier;
a host data encoder to encode an overt persistent digital channel containing a host signal on the at east one signal carrier;
a hardware modulator coupled to the oscillator and the host data encoder to modulate a non-persistent channel onto the at least one signal carrier; and
the non-persistent channel encoded onto the at least one signal carrier by timing variation of the host signal, the non-persistent channel including access data for accessing hidden information in the host signal, wherein the access data includes at least one of a stencil, a code book and a decryption key.

2. The system of claim 1, wherein the host signal is an intelligible work of nominal information.

3. The system of claim 1, wherein the host signal is encrypted and the access data is an encryption key.

4. The system of claim 3, wherein the encrypted host signal is encoded with a code book to reduce entropy.

5. The system of claim 1, wherein the timing variation is less than a level of timing stability for detecting and capturing the host signal.

6. The system of claim 1, further comprising:
a processor coupled to receive the host signal from the at least one signal carrier; and
a high stability oscillator producing a reference signal coupled to the processor for use in reading pulse timing variations of the host signal, wherein the reference signal has a stability greater than the level of timing variations of the host signal; wherein the timing variations of the host signal are smaller than the sampling period for detecting and capturing the data stream.

7. The system of claim 1, wherein the host signal is a digital data stream, and further wherein the timing variations are pulse timing variations.

8. A method for sending data on a signal carrier, comprising:
providing, by a hardware oscillator, at least one signal carrier;
encoding, using a host data encoder, an overt persistent digital channel containing a host signal on the at least one signal carrier;
modulating, using a hardware modulator coupled to the oscillator and the host data encoder, a non-persistent channel onto the at least one signal carrier, the non-persistent channel encoded onto the at least one signal carrier by timing variation of the host signal, the non-persistent channel including access data for accessing hidden information in the host signal, wherein the access data includes at least one of a stencil, a code book and a decryption key;
reading the timing variations from the host signal for separating the access data from the carrier signal and the host signal; and
accessing the hidden data using the access data.

9. The method of claim 8, wherein the host signal is an intelligible work of nominal information.

10. The method of claim 8, wherein the host signal is encrypted and the access data is an encryption key.

11. The method of claim 10, further comprising encoding the host signal with a code hook to reduce entropy, prior to encoding the host signal with the non-persistent channel.

12. The method of claim 8, wherein the pulse timing variation is smaller than the sampling period for detecting and capturing the host signal.

13. The method of claim 8, wherein the host signal is a digital data stream, and further wherein the timing variations are pulse timing variations.

14. The method of claim 8, wherein the host signal is an analog signal.