Systems and methods of secure coding for physical layer communication channels

Systems and methods of securely communicating from a sender device to a receiver device on a communication channel are disclosed. One disclosed method is for securely communicating from a sender device to a receiver device on a main channel when an eavesdropper device is listening on an eavesdropper channel. The main channel has an signal-to-noise ratio SNRM, and the eavesdropper channel has a signal-to-noise ratio SNRE. The method comprises encoding a message at a physical layer with a secure error correcting code (SECC) to produce an encoded message, and transmitting the encoded message on the main channel. The SECC has a set of defined characteristics such that when the eavesdropper device is more than a predetermined distance Z from the sender, at least a predefined fraction of the message is unreliable, where the predefined fraction of unreliable bits renders the eavesdropper unable to reliable decode messages on the main channel.

FIELD OF THE DISCLOSURE

The present disclosure relates to data communication, and more specifically, to secure coding for physical layer communication channels.

BACKGROUND

The conventional method of providing secure communication over a channel uses cryptography. Cryptography relies on the existence of codes that are “hard to break”: that is, one-way functions that are believed to be computationally infeasible to invert. Therefore, cryptography is vulnerable to an increase in computing power or the development of more efficient attacks. Furthermore, the assumptions about the hardness of certain one-way functions have not been proven mathematically, so cryptography is vulnerable if these assumptions are incorrect.

Another weakness of cryptography is the lack of no precise metrics or absolute comparisons between various cryptographic algorithms, showing the trade off between reliability and security as a function of the block length of plaintext and ciphertext messages. Instead, a particular cryptographic algorithm is considered “secure” if it survives a defined set of attacks, or “insecure” if it does not.

Cryptography as applied to some media (e.g., wireless networks) also requires a trusted third party as well as complex protocols and system architectures. Therefore, a need exists for these and other problems to be addressed.

SUMMARY

Systems and methods of providing opportunistic security for physical communication channels are disclosed. One disclosed method is for securely communicating from a sender device to a receiver device on a main channel when an eavesdropper device is listening on an eavesdropper channel. The main channel has an signal-to-noise ratio SNRM, and the eavesdropper channel has a signal-to-noise ratio SNRE. The method comprises encoding a message at a physical layer with a secure error correcting code (SECC) to produce an encoded message, and transmitting the encoded message on the main channel. The SECC has a set of defined characteristics such that when the eavesdropper device is more than a predetermined distance Z from the sender, at least a predefined fraction of the message is unreliable. The predefined fraction of unreliable bits renders the eavesdropper unable to reliably decode messages on the main channel.

One disclosed system is for securely communicating from a sender device to a receiver device on a main channel when an eavesdropper device is listening on an eavesdropper channel. The main channel has an signal-to-noise ratio SNRM, and the eavesdropper channel has a signal-to-noise ratio SNRE. The system comprises an encoder and a transmitter. The encoder is configured to encode a plurality of bits at a physical layer with a secure error correcting code (SECC) to produce a plurality of encoded bits. The transmitter is configured to transmit the encoded plurality of bits on the main channel. The SECC has a set of defined characteristics such that when the eavesdropper device is more than a predetermined distance Z from the sender, a bit error probability on the eavesdropper channel does not exceed a predetermined security threshold while a bit error probability on the main channel does exceed a predetermined reliability threshold. The plurality of encoded bits includes a fraction of unreliable bits which render the eavesdropper unable to reliably decode messages on the main channel.

Also disclosed is a radio frequency identification (RFID) tag for securely communicating from the RFID tag to an RFID reader on a main channel when an eavesdropper device is listening on an eavesdropper channel. The main channel has an signal-to-noise ratio SNRM, and the eavesdropper channel has a signal-to-noise ratio SNRE. The system comprises an encoder and a transmitter. The encoder is configured to encode a plurality of bits at a physical layer with a secure error correcting code (SECC) to produce a plurality of encoded bits. The transmitter is configured to transmit the encoded plurality of bits on the main channel. The SECC has a set of defined characteristics such that when the eavesdropper device is more than a predetermined distance Z from the sender, at least a predefined fraction of the message is unreliable. The predefined fraction of unreliable bits renders the eavesdropper unable to reliably decode messages on the main channel.

DETAILED DESCRIPTION

Symmetric encryption uses a key to transform a message into a form that is unreadable to anyone that does not have the key. Since the key itself is a shared secret, this form of encryption relies on a method of providing the sender's key to the receiver in a secure manner. The systems and methods disclosed herein exploit naturally-occurring properties of the communication channel itself, at the physical layer, which allow the sender and the receiver to generate the same key, rather than having the sender transmit the key to the receiver, as occurs in conventional cryptographic solutions. In some embodiments, the distilled key is used by a higher protocol layer to encrypt messages, using, for example, standard secret key encryption algorithms. In other embodiments, the key distilled at both sides is used as a one-time pad to provide perfect secrecy.

FIG. 1is a block diagram of an environment in which one embodiment of a system and method for providing opportunistic security for physical communication channels is located. A system100includes two devices,110S and110R, each of which includes a physical layer component120and a higher layer component130. At the physical layer, sender device110S uses two different time periods to transmit two different kinds of information to receiver device110R: random symbols140are transmitted during some time periods150; and coding information160is transmitted during other time periods170. Both sender110S and receiver110R then use an algorithm to combine coding information160with random symbols140to distill a key180.

Once discovered by each side, key180is then communicated from physical layer component120in each device110to the corresponding higher layer component130in the same device110. After using key180to encrypt a message, higher layer component130in sender device110S transmits the encrypted message190to receiver device110R. Higher layer component130in receiver device110R uses key180to decrypt message190.

A few examples of higher protocol layer130are wired equivalent privacy (WEP) at the media access control (MAC) layer, internet protocol security (IPSec) at the network layer, and secure sockets layer (SSL) at the application layer. However, a person of ordinary skill in the art would understand that the key discovery techniques disclosed herein can be used by any protocol layer130above the physical layer. Such a person will also understand that althoughFIG. 1, and other figures herein, illustrate example scenarios in which device110S acts as a sender and device110R acts as a receiver, each device is capable of acting as both a transmitter and a receiver.

The physical layer of the channel between sender device110S and receiver device110R will now be described in more detail in connection with the block diagram ofFIG. 2. System200includes devices110, which are in communication over a main channel210. System200also includes a third device220, which is capable of listening to (eavesdropping on) transmissions on main channel210, using an eavesdropper channel230. Eavesdropper220is passive with respect to main channel210; eavesdropper220does not jam main channel210, insert bits on main channel210, etc.

At the physical layer, both channels can be modeled as including noise inputs which affect signal quality: main channel210is affected by noise input240and eavesdropper channel230is affected by noise input250. One or both of devices110has information about the signal quality on eavesdropper channel230, and in embodiments where only one device110has this signal quality information, the information can be communicated to the other device. The techniques disclosed herein also allow for the possibility that eavesdropper220has information about the signal quality on main channel210, but the techniques insure that such information is not sufficient to allow eavesdropper220to obtain key180.

Both devices110include physical layer opportunistic security logic260. Logic260in110S cooperates with logic260in device110R to provide security at the physical layer in an opportunistic manner, by exploiting characteristics of noisy channels210,230in combination with information about relative signal quality of channels210and230. These techniques for exploiting channel characteristics will be described in further detail after relative signal quality is discussed connection withFIG. 3,

FIG. 3is a graph of signal quality on main channel210and eavesdropper channel230, over time. As can be seen inFIG. 3, there are time periods310during which signal quality320on main channel210is better than signal quality330on eavesdropper channel230. In this disclosure, these time periods310will be referred to as “reliable” or “secret” time periods. There are also periods of time340during which the converse is true, and message channel signal quality320is worse than wiretap channel signal quality330. These time periods340will be referred to as “unreliable” or “non-secret” time periods. Although this behavior is typical of wireless channels (where fading causes random fluctuations of the signal's amplitude and phase), a person of ordinary skill in the art would recognize that the principles described herein apply to any physical medium which experiences random noise or random fluctuations in signal strength, and thus these two different time periods.

Physical layer opportunistic security logic260exploits these varying differences in relative signal quality by communicating two different types of information from sender device110S to receiver device110R in these two different time periods. During periods310in which message channel signal quality320is better than wiretap channel signal quality330—i.e., during secret periods—random symbols140are sent over main channel210. In the example embodiments described herein, logic260in sender device110S transmits these random symbols140. In other embodiments, a fourth party (e.g., a broadcast satellite) transmits random symbols140.

During periods340in which message channel signal quality320is worse than wiretap channel signal quality330—i.e., during non-secret periods—coding information160is sent over main channel210. Thus, there is a correspondence between the time periods inFIG. 3and the time periods inFIG. 1: the secret periods310inFIG. 3correspond to transmit-random-symbols periods160inFIG. 1, and the non-secret periods340correspond to transmit-coding-information periods170.

During good-quality-on-message-channel periods310, receiver device110R accumulates random symbols140but does not use the bits represented by the symbols. After coding information160has been communicated during bad-quality-on-message-channel periods340, sender110S and receiver110R combine this additional coding information160with the accumulated random symbols140to produce key180(seeFIG. 1).

According to the principles of information-theoretic security, eavesdropper220cannot determine key180under these conditions. Information-theoretic security principles show that system200has positive secrecy capacity during good-quality-on-message-channel periods, or reliable periods,310. As will be described in further detail below, sender device110S and receiver device110R share common randomness through the random symbols140transmitted by sender device110S during reliable periods310. This transmission results in a set of symbols which is correlated between sender and receiver. Information-theoretic security principles also show that system200has zero secrecy capacity during bad-quality-on-message-channel periods, or unreliable periods,340. Coding information160is transmitted during unreliable periods340, and receiver device110R uses this coding information160to recover the bits represented by already-transmitted random symbols140. The code is designed to match the secrecy capacity of a particular system: the strength of the code guarantees that legitimate receiver device110R can recover a sequence of bits identical to those of the transmitter.

Since system200has (by definition) zero secrecy capacity during unreliable periods340, it is possible for eavesdropper220to obtain some of the information that is transmitted during these unreliable periods340. In fact, information theoretic security principles can quantify the maximum amount of information learned by eavesdropper220, regardless of particular decoding methods which eavesdropper220might use. However, an additional step (privacy amplification) taken by sender110S and receiver110R after the reconstruction guarantees that eavesdropper220can obtain no information from the amplified reconstructed bit sequence. Since the amplified and reconstructed bit sequence can be used as a key180by both sides, it follows that the techniques disclosed herein allow key180to be generated by both sides in a manner that precludes eavesdropper220from obtaining key180, and thus the techniques provide secure communication.

FIG. 4is a sequence diagram of one embodiment of physical layer opportunistic security logic260. Sequence400starts when logic260detects that message channel signal quality320is better than wiretap channel signal quality330(i.e., during a reliable period310). A person of ordinary skill in the art would be familiar with detection using standard channel estimation techniques, such as pilot-assisted symbol estimation, etc. During reliable periods310, sender110S transmits (410) over main channel210a series of symbols (X) selected at random from a symbol set. In some embodiments, the symbols are quadrature amplitude modulation (QAM) symbols.

After the random symbol transmission410, sender110S and receiver110R share a set of correlated continuous-valued symbols. Since continuous values are used, extracting a sequence of common bits from these continuous sequences is not straightforward, and standard coding techniques cannot be applied directly. Therefore, the systems and methods disclosed herein use multilevel coding. Multilevel coding quantizes the continuous symbols and then assigns a binary label to each of the quantized values. Although basic principles of multilevel coding have been proposed for use in general communication, here the use of multilevel codes is extended to the reconciliation of correlated sequences. In some embodiments, the number of symbols, the amplitudes of the symbols, and the probability distribution of the symbols are all optimized so that information is transmitted at a rate close to channel capacity, while still satisfying the power constraint of main channel210.

Both sender110S and receiver110R map (420) the received symbols (X and Y respectively) to a bit sequence. However, since some amount of noise may be present on main channel210, the bit sequence Q(Y) produced by receiver110R may differ from the bit sequence Q(X) produced by sender110S. That is, bit sequence Q(Y) may contain errors.

When logic260detects that message channel signal quality320is worse than wiretap channel signal quality330(i.e., during unreliable periods340), sender110S generates (430) error-correcting (coding) information160from the bit sequence Q(X), and transmits (440) coding information160over main channel210. During these unreliable periods340, receiver110R decodes (450) coding information160and uses this information to recover or reconcile the original bit sequence Q(X). In some embodiments, coding information160takes the form of a low-density parity-check code (LDPC). In other embodiments, coding information160takes the form of a turbo code.

After reconciliation, sender110S communicates (460) a random function over main channel210, and each side applies (470) that random function to reconciled bit sequence Q(X). This application is also known as privacy amplification, and the result is secure key180. In some embodiments, this random function is a universal hash function, with the property of producing an output sequence that is in general much smaller than the input sequence.

Notably, the reconciliation and privacy amplification steps, using coding information160already transmitted during a reliable period310, may be conducted over several disjoint unreliable periods340. Furthermore, in some embodiments coding information160is transmitted in some reliable periods310as well as unreliable periods340, to ensure some minimum amount of time is available for processing random symbols are processed.

FIGS. 5A-Eare block diagrams illustrating an example scenario with sender110S, receiver110R, and eavesdropper220. Sender110S and receiver110R communicate over main channel210, which is subject to noise input240. Eavesdropper220listens on eavesdropper channel230, which is subject to noise input250.

FIG. 5Aillustrates the behavior of the parties during reliable periods310. As described earlier, sender110S transmits over main channel210a sequence of random symbols140. In this diagram, the symbol waveforms as seen by sender110S, receiver110R, and eavesdropper220are shown as X, Y, and Z, respectively, while the sequence of quantized bits detected by the three parties are shown as Q(X), Q(Y) and Q(Z), respectively. In this example, the originally transmitted bit sequence Q(X) is 10110. Since main channel210is subject to noise, the sequence Q(Y) seen by receiver110R is slightly different: 10101. Since transmission of random symbols occurs during reliable periods310, in which message channel signal quality320is better than wiretap channel signal quality330, the sequence Q(Z) seen by eavesdropper220will, on average, contain more errors. Here, Q(Z) is 11011, which contains three bit errors as compared to two bit errors in Q(Y).

FIG. 5Billustrates the behavior of the parties during unreliable periods340. As described earlier, sender110S transmits coding information160which allows receiver110R to reconstruct the original bit sequence Q(X) from the received—and possibly errored—bit sequence Q(Y), while also preventing eavesdropper220from reconstructing the original sequence. In this example, the error correcting code is a single parity bit protecting a group of three bits, so the transmitted code C1(510) indicates even parity. The first three bits in Q(Y) were received by receiver110R with even parity, so no error is detected by receiver110R and the first three bits in Q(Y) remain as is. Eavesdropper220also receives code C1, but the bits in Q(Z) contain more errors, since wiretap channel signal quality330was worse when Q(Z) was received. Thus, the first three bits in Q(Z) still contain errors, even after code C1is received.

The reconciliation phase continues as illustrated inFIG. 5C. The transmitted code C2(520) also indicates even parity. Here, the second group of three bits in Q(Y) were received with odd parity, so an error is detected and the second group of three bits in Q(Y) are corrected to 010. The reconciliation phase is completed inFIG. 5D, where transmitted code C3(530) indicates even parity, and the last three bits in Q(Y) remain unchanged. As before, Q(Z) as seen by eavesdropper220still contains errors, even after all three codes C1, C2and C3are received.

The final phase for key generatio is illustrated inFIG. 5E. At the end of the reconciliation function, the bit sequence Q(Z) is still correlated with sequence Q(X), which means eavesdropper220can guess some information about original bit sequence Q(X). To amplify the amount of privacy, sender110S broadcasts a random function, which is received by receiver110R and eavesdropper220. Each party applies the random function to Q(X), Q(Y), and Q(Z), respectively. Application of the random function by sender110S and receiver110R produces the same key180, while eavesdropper220produces a different key540. Information-theoretic security principles guarantee that each bit of the eavesdropper-generated key560has a particular degree of independence from corresponding bits of key180. That is, the error correcting code and the privacy amplification function are designed to guarantee that key540is as independent of key180as is desired, which means that eavesdropper220can extract no information about key180.

FIG. 6is a block diagram of the multilevel coder and encoder used by some embodiments of physical layer opportunistic security logic260. As described earlier, noise input240introduces discrepancies between the received data as seen by receiver110R and the random symbols sent by sender110S. Sender110S generates reconciliation, or coding, information160to correct these discrepancies. Logic260within sender device110S includes a bit labeler610which receives transmitted symbols X and assigns an m-bit binary label to each symbol X. A multilevel coder620(e.g., a LDPC coder) successively computes a series of m syndromes s. Syndromes s are transmitted on main channel210during reliable periods310.

Logic260within receiver device110R recovers syndromes s. Random symbols Y (previously received during unreliable periods340) are processed by a demapper630to produce a bit sequence which, in combination with syndromes s, is decoded by a multistage decoder650. Thus, decoder650uses syndromes s as side information.

FIG. 7is a diagram illustrating a timeline700for generating and using multiple keys over time. A time period710in which a first key is generated is followed by another time period720in which the first key is used for encryption. A second key is generated in time period730, and this second key is used during time period740. Similarly, a third key is generated in time period750, and this third key is used during time period760. As explained earlier, each of key generatio periods710,730,750is itself composed of reliable sub-periods during which random symbols are distributed and unreliable sub-periods during which reconciliation occurs. In this manner, key180is periodically refreshed, so that even if eavesdropper220guesses one instance of the key, that key instance is in use for only a short period of time.

In some embodiments, the frequency of key generatio is based on characteristics of main channel210, eavesdropper channel230, or both (e.g., the ratio of reliable periods310to unreliable periods340, the ratio of average main channel signal quality to average eavesdropper channel signal quality, or the absolute signal quality of either channel). In some embodiments, physical layer component120(seeFIG. 1) generates the key in response to a request by higher-layer component130. In other embodiments, physical layer component120generates the key of its own accord, without a request by higher-layer component130.

In the embodiments discussed above, a key was generated at both the sender and receiver by combining information transmitted during a positive-secrecy time period (transmission of random symbols) with information transmitted during a zero-secrecy time period (coding information used to reconcile the correlated symbols). Other embodiments will now be described which take advantage of environments in which the main message channel (between “friendly” transmitter and “friendly” receiver) always has positive secrecy capacity.

Positive secrecy capacity is assured when the eavesdropper is more than a certain distance away from the friendly (message) transmitter, thus guaranteeing that the signal quality on the message channel is better than the signal quality on the eavesdropper channel. In such environments, all transmission periods are considered to be good-quality-on-message-channel periods310. The embodiments described below in connection withFIGS. 8-11utilize secure error correcting codes (SECCs) at the physical layer to insure communication between the friendly parties that is both reliable and secure.

In the real world, this assumption is perhaps most reasonable when the distance between friendly transmitter and the friendly receiver is on the order of a few meters. One non-limiting example of such a scenario is an radio frequency identification (RFID) tag transmitting to a RFID reader. In such cases, an eavesdropper that is on the order of tens of meters away from the friendly transmitter has an signal quality that is hundreds of times worse than that of the main message channel (since the signal power is proportional to the square of the distance). However, the techniques described herein are applicable any time the message channel has positive secrecy capacity. The laws of physics gurantees that the signal quality will be lower for the eavesdropper as long as the eavesdropper is physically further away from the friendly transmitter than the friendly receiver is. The relative antenna sizes of the friendly parties and the eavesdropper determine the specific distance between the eavesdropper and the friendly transmitter that is required for positive secrecy capacity to be obtained. In other words, the techniques described below can guarantee a perfect secrecy zone of size Z around the friendly transmitter, given a specific set of antenna sizes.

FIG. 8is a block diagram of a sender device and a receiver device utilizing secure error correcting codes at the physical layer. System800includes devices810S and810R which are in communication over a main channel820. Main channel820is subject to a noise input830. System800also includes another device840which is capable of listening to (eavesdropping on) transmissions on main channel820, over an eavesdropper channel850. Eavesdropper channel850is subject to a noise input860. Eavesdropper840is passive with respect to main channel820; eavesdropper840does not jam main channel820, insert bits on main channel820, etc. In the embodiments discussed below in connection withFIGS. 8-11, channels820and850are wireless. A non-limiting list of examples of wireless technologies includes: radio frequency identification (RFID) networks (e.g., ISO 14443, ISO 18000-6); wireless local area networks (e.g. IEEE 802.11, commonly known as WiFi); wireless wide area networks (e.g., WiMAX or IEEE 802.16); wireless personal area networks (e.g., Bluetooth, IEEE 802.15.4, commonly known as ZigBee) and wireless telephone networks (e.g., CDMA, GSM, GPRS, EDGE). Although the embodiments discussed below in connection withFIGS. 8-11involve wireless channels820and880, the principles disclosed herein apply also apply to wired channels.

Each device810includes a physical layer component870, where the physical layer870incorporates secure error correcting coding (SECC) logic880. Although device810S is described as operating a sender and device810R as a receiver, a person of ordinary skill in the art would understand that each device810is capable of acting as both a transmitter and a receiver.

FIG. 9is a diagram of devices810S and810R utilizing secure error correcting codes at the physical layer.FIG. 9illustrates a feature which is exploited by some embodiments when devices810are in close proximity to each other relative to the distance from eavesdropper840. When the distance910from sender810S to receiver810R is much smaller than the distance920from sender810S to eavesdropper840, the signal-to-noise ratio on main channel820(SNRM) is better than the signal-to-noise ratio on eavesdropper channel850(SNRE), as can be shown using basic communications theory.

The secure error-correcting coding techniques disclosed herein exploit this property to insure that information on main channel820remains secret from eavesdropper840while also providing high reliability on main channel820. The secure error correcting code (SECC) used by logic880provides a perfect secrecy zone930within a given distance Z from sender810S. In the example embodiment shown inFIG. 9, perfect secrecy zone930is a circle, so that Z is the radius of that circle. Outside perfect secrecy zone930, the signal-to-noise ratio on eavesdropper channel850(SNRE) results in a bit error rate on eavesdropper channel850(BERE) that is high enough to guarantee that a specific percentage of the bits obtained from transmissions by sender810S are unreliable. Logic880uses an SECC which guarantees that this unreliable information renders eavesdropper840unable to reliably decode messages sent on main channel820. A suitably designed SECC ensures that the bit error rate experienced by the eavesdropper is higher than the bit error rate produced by a conventional error correcting code. In fact Shannon's information theory can be used to show the existence, in certain situations, of SECCs that make the reliability of the eavesdropper's information as low as possible.

To do so, logic880uses a secure error correcting code (SECC) with specific properties or characteristics. These properties or characteristics are related to SNRMand SNRE, where SNRMand SNREare turn related to the distance between sender810S and receiver810R, and the distance from sender810S to eavesdropper840(respectively).FIG. 10is a graph1000illustrating bit error probability performance of a secure error correcting code used by an example embodiment of logic880. As can be seen in the plot of SNR vs. BER behavior in graph1000, for a given expected SNR on main channel820(SNRM), the SECC used by logic880produces a bit error rate (on main channel820) which exceeds a predetermined reliability threshold1010. For a given expected SNR on eavesdropper channel850, the same SECC produces a bit error rate (on eavesdropper channel850) which is less than a predetermined security threshold1020. The SECC used by logic880could thus be described as exhibiting a sharp waterfall region (sharp dropoff between1010and1020) as well as high BER at low SNRs. In some embodiments, the SECC used by logic880is based on a linear block code. In other embodiments, the SECC is a turbo code. In still other embodiments, the SECC is a low density parity check code.

Various embodiments of SECC logic880achieve a larger or smaller perfect secrecy zone1030by using an SECC with a slightly different SNR vs. BER curve. For example, a larger perfect secrecy zone1030is achieved by using a code which has a lower BER at a high SNR as compared toFIG. 10. In other words, the predetermined reliability threshold1010moves to the right. Codes that provide a larger secrecy zone may be relatively complex. A smaller perfect secrecy zone1030is achieved by using a code in which the predetermined reliability threshold1010moves to the left as compared toFIG. 10.

Some embodiments of devices810S and810R include encryption at higher layers of the protocol stack in addition to the security provided by SECC logic880at the physical layer. A few examples of encryption at a higher layer are wired equivalent privacy (WEP) at the media access control (MAC) layer, internet protocol security (IPSec) at the network layer, and secure sockets layer (SSL) at the application layer. However, the SECC techniques disclosed herein can be used in combination with any protocol layer above the physical layer. When using this combination principles of information-theoretic security show that as long as the eavesdropper is more than a certain distance away from the friendly transmitter and receiver, the eavesdropper will necessarily have a number of errors after decoding and that this number of errors, when combined with a particular cryptographic code, will render the eavesdropper virtually unable to decode the message. Furthermore, the SECC techniques described herein allow flexibility in the level of security that is required against an eavesdropper. For example, if it is known that the eavesdropper is more than a certain distance away, then the SECC can be less complex.

FIG. 11is a block diagram illustrating selected components of one embodiment of a physical layer870. Sender physical layer870S includes a framer1110, an encoder1120, and a modulator1130. Framer1110operates on a message from a higher protocol layer. The message comprises a stream of bits1135, and produces a block1145, which may include header and trailer information. Block1145is encoded by SECC encoding logic1140within encoder1120, producing one or more encoded bits1155. Encoded bits1155are modulated by modulator1130and transmitted over main channel820to receiver physical layer870R. Receiver physical layer870R inculdes a demodulator1150, a decoder1160, and a framer1170. Symbols received on main channel820are mapped to bits1175by demodulator115, and bits1175are decoded by SECC decoding logic1180within decoder1160. The group of decoded bits1185are received by framer1190, which strips off header/trailer bits as necessary to reveal the orginally transmitted message. The message may then be passed up to a higher protocol layer.

In some embodiments, one side of the communication channel has less processing or computing capabilities than the other. In some embodiments, the properties of the communication channel may be asymmetrical (e.g., 10 Mbit/sec in one direction and 1 Mbit/sec in the other). In such embodiments, one side may use different modulation and/or framing techniques when transmitting than the other side does. As a non-limiting example, one side may transmit using quadrature amplitude modulation with 16 different symbols (QAM16) while the other side may transmit using quadrature amplitude modulation with 64 different symbols (QAM64).

FIG. 12is a hardware block diagram of a computer system1200which can be used to implement device110in accordance with various embodiments of the systems and methods of providing opportunistic security for physical communication channels, or to implement device810in accordance with various embodiments of the systems and methods of utilizing secure error correcting codes at the physical layer. Computer system1200contains a number of components that are well known in the art of data communications, including a processor1210, a network interface1220, memory1230, and non-volatile storage1240. These components are coupled via bus1250. A person of ordinary skill in the art would understand that the network interface1220may support different medias, speeds, etc. Examples of non-volatile storage include, for example, a hard disk, flash RAM, flash ROM, EEPROM, etc. Memory1230contains physical layer opportunistic security logic260fromFIG. 1and/or SECC logic880fromFIG. 8, which programs or enables processor1210to perform the functions of logic260or logic880. Omitted fromFIG. 12are a number of conventional components, known to those skilled in the art, that are not necessary to explain the operatio of computer system1200.

Device110can be implemented in software, hardware, or a combination thereof. In some embodiments, the device, system, and/or method is implemented in software that is stored in a memory and that is executed by a suitable microprocessor, network processor, or microcontroller situated in a computing device. In other embodiments, the device, system and/or method is implemented in hardware, including, but not limited to, a programmable logic device (PLD), programmable gate array (PGA), field programmable gate array (FPGA), an application-specific integrated circuit (ASIC), a system on chip (SoC), and a system on packet (SoP).

Device110can be embodied in any computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device. Such instruction execution systems include any computer-based system, processor-containing system, or other system that can fetch and execute the instructions from the instruction execution system. In the context of this disclosure, a “computer-readable medium” can be any means that can contain, store, communicate, propagate, or transport the program for use by, or in connection with, the instruction execution system. The computer readable medium can be, for example but not limited to, a system or propagation medium that is based on electronic, magnetic, optical, electromagnetic, infrared, or semiconductor technology.

Specific examples of a computer-readable medium using electronic technology would include (but are not limited to) the following: an electrical connection (electronic) having one or more wires; a random access memory (RAM); a read-only memory (ROM); an erasable programmable read-only memory (EPROM or Flash memory). A specific example using magnetic technology includes (but is not limited to) a portable computer diskette. Specific examples using optical technology include (but are not limited to) an optical fiber and a portable compact disk read-only memory (CD-ROM).

Any process descriptions or blocks in flowcharts would be understood as representing modules, segments, or portions of code which include one or more executable instructions for implementing specific logical functions or steps in the process. As would be understood by those of ordinary skill in the art of the software development, alternate implementations are also included within the scope of the disclosure. In these alternate implementations, functions may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order, depending on the functionality involved.

The foregoing description has been presented for purposes of illustratio and description. It is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. The implementations discussed, however, were chosen and described to illustrate the principles of the disclosure and its practical application to thereby enable one of ordinary skill in the art to utilize the disclosure in various implementations and with various modifications as are suited to the particular use contemplated. All such modifications and variation are within the scope of the disclosure as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly and legally entitled.