CN112166464B

CN112166464B - Cryptographic key creation using optical parameters

Info

Publication number: CN112166464B
Application number: CN201980035653.4A
Authority: CN
Inventors: A·A·哈桑; R·昆茨
Original assignee: Microsoft Technology Licensing LLC
Current assignee: Microsoft Technology Licensing LLC
Priority date: 2018-05-29
Filing date: 2019-05-14
Publication date: 2024-02-27
Anticipated expiration: 2039-05-14
Also published as: CN112166464A; WO2019231655A1; EP3785252A1

Abstract

A cryptographic key generator for a first optical transceiver, comprising: a photodetector that receives the continuous wave optical beam received from the second optical transceiver via the optical channel. The generator samples and quantizes a signal from the photodetector during a plurality of intervals to generate a respective sample representing a respective number of photons incident on the photodetector during each of the plurality of intervals. The generator creates a first cryptographic key from the plurality of digital values. The second optical transceiver receives the continuous wave optical beam from the first transceiver and performs the same function to create a second cryptographic key. The first cryptographic key matches the second cryptographic key due to the reciprocal nature of the channel.

Description

Cryptographic key creation using optical parameters

Background

Many cryptographic methods employ a key server or otherwise exchange encryption keys among multiple devices. Other devices generate and exchange keys or partial keys between two or more devices. Obtaining a cryptographic key or exchanging a key from a server risks intercepting the key and may therefore maliciously decrypt data encrypted with the key. Efficient cryptographic key distribution is an important element of secure communication systems. While the current approach can ensure efficient key distribution in many cases, it is still vulnerable to attack.

Disclosure of Invention

This summary is not an extensive overview of the claimed subject matter. It is intended to neither identify key elements of the claimed subject matter nor delineate the scope of the claimed subject matter. Its sole purpose is to present some concepts of the claimed subject matter in a simplified form as a prelude to the more detailed description that is presented later.

According to one aspect, a first optical transceiver receives a first continuous wave optical beam at a first photodetector from a second optical transceiver via an optical channel. The first optical transceiver samples and digitizes a signal from the first photodetector representative of photons incident on the photodetector during each of a first plurality of intervals. The first optical transceiver creates a cryptographic key from the digitized sample.

According to another aspect, the first optical transceiver further comprises: a light source configured to generate a second light beam; and an optical coupler configured to selectively direct a second light beam from the light source to an optical channel and to direct a first light beam from the optical channel to the photodetector. The optical coupler is configured to: directing a first light beam from the optical channel to the photodetector during a first plurality of intervals; and directing a second light beam from the light source to the optical channel during a second plurality of intervals different from the first plurality of intervals, resulting in a matched cryptographic key being created by the second optical transceiver.

The following description and the annexed drawings set forth in detail certain illustrative aspects of the claimed subject matter. These aspects are indicative, however, of but a few of the various ways in which the principles of the claimed subject matter may be employed and the claimed subject matter is intended to include all such aspects and their equivalents. Other advantages and novel features of the claimed subject matter will become apparent from the following detailed description when considered in conjunction with the drawings.

Drawings

Fig. 1A and 1B are block diagrams of an exemplary optical network.

Fig. 2 is a block diagram of an optical network showing details of two exemplary optical transceivers.

Fig. 3A is a flow chart illustrating the operation of an exemplary key generator that may be used in the network shown in fig. 1A.

Fig. 3B and 3C are flowcharts showing details of the flowchart in fig. 3A.

Fig. 4A and 4B are flowcharts illustrating a method for generating an encryption key from a set of M symbols.

Fig. 5 is a flowchart illustrating the operation of another exemplary key generator that may be used in the network shown in fig. 1B.

Fig. 6A and 6B are graphs of power versus time for describing exemplary embodiments.

Detailed Description

The disclosed embodiments describe such methods: by means of the method, two optical transceivers connected by a common optical channel can independently create matching cryptographic keys while exchanging little or no information about the keys. These embodiments provide the technical advantages of: the two optical transceivers may create a matching key and use the key to encrypt and decrypt data for secure communications over a channel between the two optical transceivers without exchanging keys or key-related information over any channel. Another advantage provided by the exemplary embodiments is that: the communications optical transceiver may determine the key immediately prior to initiating the encrypted communications.

The optical channel between two optical transceivers is reciprocal (reciprocal); the optical beams transmitted from the first optical transceiver to the second optical transceiver and from the second optical transceiver to the first optical transceiver experience substantially the same channel characteristics. According to poisson distribution, photons transmitted from a continuous wave light source through one end of an optical channel are received and sensed at the other end of the optical channel. The poisson distribution may be approximated by a gaussian distribution having an average value λ corresponding to the average number of photons sensed during the predetermined interval. In this approximation, the variance of the gaussian distribution is also λ. The value of lambda depends on the characteristics of the light source, the optical channel and the detector. Thus, when similar devices are used on both sides of the optical channel, each optical transceiver senses a similar average number of photons with a similar variance during a predetermined interval. The two optical transceivers can capture a change in the number of photons and convert it into a cryptographic key. Due to the reciprocity of the optical channels, both optical transceivers receive a similar number of photons during the corresponding interval. Each optical transceiver may then encrypt data using its cryptographic key for transmission to another optical transceiver and decrypt data received from the other optical transceiver. Although the embodiments described below utilize one or more optical fibers in an optical channel, it is contemplated that any type of optical waveguide (e.g., formed of glass, crystal, or semiconductor) may be used in an optical channel. Alternatively or additionally, it is contemplated that each optical transceiver may direct the collimated light beam onto another optical transceiver through an intermediate medium (e.g., air, water, vacuum, or other medium). In this case, the optical channel may comprise a medium between two optical transceivers.

Because the number of photons sensed during each predetermined interval depends on the characteristics of the two optical transceivers and the optical channels connecting the optical transceivers, only two optical transceivers may suffer from these characteristics. A third optical transceiver attempting to intercept communications (e.g., via an optical coupler briefly coupled to the optical channel) will not be able to create a key or decode the communications because photons sensed by the third party will be controlled by a different poisson distribution. The third optical transceiver is not able to intercept the key or key information because the cryptographic key or information about the cryptographic key is not exchanged on any channel. Embodiments also provide the advantage that: the keys created in each of the two optical transceivers may be updated appropriately to provide additional security. Because keys are created based on the current characteristics of the individual light sources, optical channels, and photodetectors, cryptographic keys created at different times may be affected by different characteristics (e.g., thermal effects) so that each new key may be different from the previously created key.

The created cryptographic key may be used, for example, in a symmetric encryption algorithm such as, but not limited to, data Encryption Standard (DES), triple DES, blowfish, advanced Encryption Standard (AES), rivest Cipher 4 (RC 4), RC5, or RC6 to encrypt and/or decrypt data.

As a preliminary matter, some of the drawings describe concepts in the context of one or more structural components variously referred to as functions, modules, features, elements, etc. The various components shown in the figures may be implemented in any manner, such as software, hardware, firmware, or combinations thereof. In some cases, the various components shown in the figures may reflect the use of corresponding components in an actual implementation. In other cases, any single component illustrated in the figures may be implemented by multiple actual components. The depiction of any two or more separate components in the figures may reflect different functions performed by a single actual component.

Other figures depict these concepts in flow chart form. In this manner, certain operations are described as constituting distinct blocks performed in a particular order. Such implementations are exemplary and non-limiting. Some of the blocks described herein can be grouped together and performed in a single operation, some of the blocks can be broken up into multiple constituent blocks, and some of the blocks can be performed in an order different from that illustrated herein, including in a parallel manner. Blocks shown in the flowcharts can be implemented by software, hardware, firmware, manual processing, or the like. As used herein, hardware may include microprocessors, digital Signal Processors (DSPs), microcontrollers, computer systems, discrete logic components, and/or custom logic components, such as Field Programmable Gate Arrays (FPGAs), application Specific Integrated Circuits (ASICs), programmable Logic Arrays (PLAs), and the like.

With respect to terms, the phrase "configured to" encompasses any manner in which any kind of functionality can be constructed to perform the identified operations. The functions can be configured to perform operations using, for example, software, hardware, firmware, etc. For example, the phrase "configured to" can refer to a logic circuit structure of hardware elements arranged to implement the associated function. The phrase "configured to" can also refer to a logic circuit structure of a hardware element of an encoded design arranged to implement the associated functionality of firmware or software. The term "module" refers to a structural element that can be implemented using any suitable hardware (e.g., processor, etc.), software (e.g., application, etc.), firmware, and/or any combination of hardware, software, and firmware. The term "logic" encompasses any functionality for performing a task. For example, each operation illustrated in the flowcharts corresponds to logic for performing that operation. The operations can be performed using software, hardware, firmware, etc. The terms "component," "system," and the like may refer to a computer-related entity, hardware, software in execution, firmware, or a combination thereof. A component may be a process running on a processor, an object, an executable, a program, a function, a subroutine, a computer, or a combination of software and hardware. The term "processor" may refer to a hardware component, such as a processing unit of a computer system, which may include a single or multi-core microprocessor, a microcontroller, and/or a Digital Signal Processor (DSP).

Furthermore, the claimed subject matter may be implemented as a method, apparatus, or article of manufacture using standard programming and engineering techniques to produce software, firmware, hardware, or any combination thereof to control a computing device to implement the disclosed subject matter. The term "article of manufacture" as used herein is intended to encompass a computer program accessible from any non-transitory computer-readable storage device or medium. The computer-readable storage medium can include, but is not limited to: magnetic storage devices such as hard disks, floppy disks, magnetic strips, optical disks, compact Disks (CDs), digital Versatile Disks (DVDs), smart cards, flash memory devices, etc. In contrast, computer-readable media (i.e., non-storage media) may additionally include communication media such as transmission media for wireless signals and the like.

Fig. 1A is a block diagram of a simple optical communication network 100 in which two optical transceivers 102 and 104 communicate via a connecting optical channel 106 comprising optical fibers. The optical fibers forming the exemplary optical channel 106 are selected such that the device may implement half-duplex and/or full-duplex communications. Fig. 1B is a block diagram illustrating another optical communication network 150. In the optical network, two optical transceivers 152 and 154 communicate over an optical channel that includes a plurality of optical fibers (e.g., 156 and 160) and a plurality of repeaters (e.g., 158 and 162) that couple the optical fibers. The repeaters 158 and 162 may, for example, filter and amplify the fibers to increase signal strength while removing out-of-band noise.

Fig. 2 is a block diagram showing details of two optical transceivers 210 and 250 coupled by an optical channel 230. For example, the optical transceiver 210 includes an optical coupler 204, a photodetector 206, a sampler/analog-to-digital converter (ADC) 208, a processor 212, a memory 214, an input/output (I/O) interface 216, a modulator 218, a light source 230, a mirror 224, and an optional pseudo-random number (PN) generator 226. The light source 220 generates a collimated light beam 222. Similarly, the exemplary optical transceiver 250 includes an optical coupler 254, a photodetector 256, a sampler/ADC 258, a processor 262, a memory 264, an I/O interface 266, a modulator 268, a light source 270, a mirror 274, and an optional pseudo-random number (PN) generator 276. The light source 270 generates a collimated light beam 272. The elements of optical transceiver 250 operate in the same manner as the corresponding elements of optical transceiver 210. Memories 214 and 264 may hold program instructions for respective processors 212 and 216 and may also hold data used in key creation, as described below. The following materials describe the operation of the elements of transceiver 210. The description also applies to the corresponding elements of the optical transceiver 250.

Each of the light sources 220 and 270 shown in the example of fig. 2 may include a semiconductor laser or a Light Emitting Diode (LED) coupled to a collimating lens (not shown). The light source may operate in one or more of the Infrared (IR), visible, or Ultraviolet (UV) spectral bands. Photodetectors 206 and 256 may include, for example, photodiodes, phototransistors, or photoresistors, and may also include a microscope objective (not shown) configured to focus light from optical coupler 204 or 254 onto photodetectors 206 or 256. To provide reciprocity between the optical transceivers 210 and 250, it is desirable that the light sources 220 and 270, photodetectors 206 and 256, and optical couplers 204 and 254 of the two optical transceivers match. As described below, the light sources 220 and 270 and the photodetectors 206 and 256 may be any such optical transceiver, so long as they have similar characteristics. Indeed, it may be advantageous to use relatively low quality devices because these devices tend to exhibit greater variability in their steady state operation than high quality devices. This greater variability may result in greater variance in successive cryptographic keys, and thus may enhance the security of data encrypted using multiple successive cryptographic keys.

Although the examples are described as using a solid state light source with electrical modulation, it is contemplated that other types of light sources may be used, such as gas lasers, chemical lasers, or dye lasers, and/or that an optical modulator, such as an electro-optical modulator (EOM) (not shown), disposed between the light source 220 or 270 and the optical coupler 204 or 254, respectively, may be used to modulate the light beam provided by the light source.

In the optical transceiver 210, the example optical coupler 204 is controlled by the processor 212 to direct the light beam from the optical channel 230 to the photodetector 206 or mirror 224 and/or to direct the light beam 222 from the light source 220 to the optical channel 230. In some embodiments, the optical coupler may be implemented as a digital micromirror (DMM) device that pivots between three positions. In the orientation shown in fig. 2, these positions are: at 135 degrees relative to the axis of the optical channel 230 to direct light from the channel 230 to the photodetector 206;315 degrees to direct beam 222 to the optical channel; and a 90 degree angle to reflect the light beam provided by optical channel 230 back to optical channel 230. In these embodiments, the DMM device may be internal to the optical coupler 204 and may function as a mirror 224.

Alternatively, the optical coupler may comprise a beam splitter or one or more light guides between the optical channel 230 and the photodetector 206, mirror 224, and light source 220. The optical couplers may also include corresponding light valves (e.g., LCDs or mechanical shutters) that may be controlled to selectively pass or block respective optical paths between the optical channel 230 and each of the photodetector 206, mirror 334, and light source 220. This second configuration may be used to implement a full duplex channel between optical transceivers 210 and 250.

The exemplary photodetector 206 produces an electrical signal proportional to the optical power of the light beam from the optical channel 230. The optical power of the light beam on the photodetector 206 is in turn related to the number of photons incident on the photodetector 206 during the sampling interval. The number of photons incident on the photodetector 206 during a sampling interval is controlled by a poisson distribution, which may be modeled by a gaussian distribution having an average number of photons per sampling interval and a variance corresponding to the average. The embodiments described below assume that the light beams received by optical transceivers 210 and 250 operate according to a similar poisson distribution.

The exemplary implementation of the embodiments also provides the advantage that: these implementations may be used in networks or systems having optical transceivers that use relatively low quality light sources and photodetectors. However, in these networks, a sampled and quantized optical signal received by one optical transceiver may have one or more symbol differences compared to a sampled and quantized optical signal received by another optical transceiver. Thus, the cryptographic key directly created from the sampled and quantized signal may not be identical in the two optical transceivers. For example, the sampled and quantized signal may exhibit low level variations due to thermal noise. In some embodiments, the quantized samples may be further processed to generate symbols that include only selected bits of the quantized samples. Furthermore, the zero value symbols may be ignored. The generated symbols correspond to photons of a continuous wave optical signal incident on the photodetector during the selected interval. As described above, the number of photons detected by the photodetector follows a poisson distribution and is determined, at least in part, by the characteristics of the optical channel.

The exemplary system may also convert non-identical keys with a relatively small amount of difference to the same key by applying the quantized samples to an ECC decoder (such as a Reed-Solomon decoder). In these embodiments, the decoder may implement a many-to-one mapping by which multiple symbol sequences are mapped into a common cryptographic key. Thus, symbol sequences generated from two sampled signals received by different optical transceivers and having a relatively small number of different quantized values may be mapped into a common cryptographic key. The number of symbol differences that can be mapped to the same value depends on the Hamming distance of the particular ECC. As described above, an ECC decoder with a large enough Hamming distance may be used to map the sampled sequence to a public key that may be used with the encryption algorithm. The ECC used by these embodiments depends on the type and length of the cryptographic key to be created, as described below.

For key creation using the embodiment shown in fig. 2, optical transceivers 210 and 250 are placed simultaneously in key creation mode. This may be accomplished, for example, using unencrypted communications between the two devices. In an exemplary key creation mode, each of the optical transceivers 210 and 250 may be assigned a predetermined amount of time to receive a continuous wave optical signal from the other transceiver in order to create a cryptographic key. In one exemplary embodiment, the optical coupler 204 of the optical transceiver 201 is first controlled by the processor 212 to direct the light beam from the optical channel 230 to the photodetector 206 while the optical transceiver 250 transmits an unmodulated continuous wave optical signal through the optical channel 230. During this interval, the photodetector 206 accumulates incident photons to generate a charge, which is then sampled by the sampler/ADC 208. In an exemplary embodiment, the sampler/ADC 208 samples the charge accumulated on the photodetector 206 after an accumulation interval between 1ns and 50 ns. In some embodiments, the ADC of the sampler/ADC 208 may be 10 per second ⁶ And 10 ⁷ The rate between samples generates 10-to 20-bit sample values. Thus, the sampler of the sampler/ADC 208 may operate at a higher rate than the ADC of the sampler/ADC 208. In particular, the sampler may obtain samples integrated by the photodetector 206 during a period between 1ns and 50ns, reset the photodetector 206, and hold the samples for a period of 100ns to 1ns for digitizing by the ADC.After digitizing the sample, the sampler allows the photodetector to accumulate charge for another sampling interval, and at the end of that interval the next value is captured and digitized. As described below, the quantized samples of the output from the sampler/ADC 208 are applied to a processor 212, and the processor 212 creates or generates a cryptographic key. The generated cryptographic key may be stored in memory 214. The optical transceiver 250 uses the same procedure to create the cryptographic key, which is expected to be the same as the cryptographic key created by the optical transceiver 210 due to channel symmetry.

The optical transceiver 250 creates its cryptographic key before, during, or after the cryptographic key is created by the optical transceiver 210. The creation of the cryptographic key by the optical transceiver 250 is similar to the creation by the optical transceiver 250 and is briefly described below. At the time of agreement between optical transceiver 210 and optical transceiver 250, optical transceiver 210 directs an unmodulated continuous wave optical beam 222 from optical source 220 through an optical coupler to optical channel 230. The optical coupler 254 of the optical transceiver 250 is configured by the processor 262 to direct the light beam from the optical channel 230 to the photodetector 256. The charge on the photodetector 256 is sampled and digitized by a sampler/ADC 258 to generate a sequence of quantized samples that are provided to a processor 262. Processor 262 converts the sequence of values into a cryptographic key that is stored in memory 264.

The pseudo-random number generators 226 and 276 shown in fig. 2 may be used to adjust the power level of the continuous beam provided by the respective optical transceivers 210 and 250 during cryptographic key creation, as described below.

After both optical transceivers 210 and 250 have created the cryptographic key, optical transceiver 210 may encrypt the known data stream and send it to optical transceiver 250. If the optical transceiver 250 is able to decrypt the known data stream using its cryptographic key, the optical transceiver 250 may send an encrypted or unencrypted acknowledgement signal to the optical transceiver 210 to indicate that the two keys match. Alternatively, each optical transceiver may encrypt known data and transmit it to another optical transceiver, and after successful decoding, store and begin using the created cryptographic key without transmitting an acknowledgement signal. If the optical transceiver 250 is not able to decrypt the data stream, the two keys do not match and both optical transceivers 210 and 250 resume the process of generating their respective cryptographic keys.

In the optical transceiver 210, the processor 212 may encrypt data provided via the I/O interface 216 using a cryptographic key. The encrypted data may then be applied to modulator 218, and modulator 218 modulates light source 220 to generate optical beam 222. To transmit the encrypted data on the optical beam 222 to the optical transceiver 250, the processor 212 controls the optical coupler 204 to direct the optical beam 222 to the optical channel 230. In the optical transceiver 250, the processor 262 encrypts data provided via the I/O interface 266 with a cryptographic key and provides the encrypted data to the modulator 268. Modulator 268 controls light source 270 to provide a modulated light beam 272 to optical coupler 254, optical coupler 254 being controlled by processor 262 to direct the modulated light beam to optical channel 230 for transmission to optical transceiver 210.

Both optical transceivers 210 and 250 create encryption keys prior to exchanging encrypted data. The keys may be created sequentially such that one optical transceiver 210 or 250 creates a cryptographic key before the other optical transceiver 250 or 210. Alternatively, the two optical transceivers may simultaneously create a key such that optical transceiver 210 generates and transmits a continuous wave optical signal to optical transceiver 250 while optical transceiver 250 generates and transmits a continuous wave optical signal to optical transceiver 210. These signals may be transmitted simultaneously (full duplex), or may be interleaved such that optical transceiver 210 receives N quantized samples, and then optical transceiver 250 receives N quantized samples until both optical transceivers have generated M symbols for creating a cryptographic key.

As described above, because the two optical transceivers 210 and 250 independently create their cryptographic keys, the keys may or may not match. Fig. 3A is a flowchart of an exemplary cryptographic key creation process 300 implemented by optical transceivers 210 and 250 to achieve matched keys, according to an example embodiment. Fig. 3A is described in the context of an optical transceiver 210. However, the same operation applies to the optical transceiver 250.

At block 310, the optical transceiver 210 creates a cryptographic key. An exemplary process for generating a cryptographic key is described below with reference to fig. 3B, 3C, 4A, 4B, and 5. At block 312, after generating the key, the processor 212 of the optical transceiver 210 encrypts the known data set with the created cryptographic key and transmits the encrypted data set to the optical transceiver 250. The processor 212 uses the modulator 218 to modulate the light source 220 with the encrypted data set while controlling the optical coupler 204 to direct the light beam 222 to the optical channel 230. The modulated optical beam containing the encrypted data is transmitted to an optical transceiver 250 via an optical channel 230. Next, at block 314, the processor 212 configures the optical coupler 204 to direct the light beam from the optical channel 230 to the photodetector 206. The optical transceiver 210 then receives, quantizes, and samples the received optical signal. The received signal may be an acknowledgement if the optical transceiver 250 successfully decrypts the data set. Alternatively, the received signal may be a known data set encrypted and transmitted by the optical transceiver 250. In this case, the processor 212 of the optical transceiver 210 applies the cryptographic key to decode the sampled data signal and compares the result with known data to determine whether decryption was successful.

The cryptographic key matches when the receiving optical transceiver receives the acknowledgement signal or is able to decrypt the known data. At block 316, if the cryptographic keys do not match, control transfers to block 310 to restart the process of generating the cryptographic keys. When a cryptographic key match is determined at block 316, block 322 stores the cryptographic key in memory 214 for encrypting data received via I/O interface 216 and for decrypting data received from optical transceiver 250 via optical channel 230.

Fig. 3B, 3C, 4A, 4B, and 5 are flowcharts describing examples of processes for block 310 to generate cryptographic keys. The creation of the encryption key by the two optical transceivers 210 and 250 may be synchronized according to a protocol known to both transceivers 210 and 250 or communication between the transceivers 210 and 250 prior to generating the encryption key. Alternatively, the optical transceivers 210 and 250 may be synchronized based on a common signal received, for example, from a GPS receiver (not shown) in each of the transceivers 210 and 250. The protocol may also include data for synchronizing clock signals in the two optical transceivers such that each of the transceivers is capable of transmitting and receiving continuous wave optical signals during intervals in which the other transceiver receives and transmits, respectively, continuous wave optical signals. Fig. 3A depicts a basic process for generating a cryptographic key that may include two optional elements. At block 324, a first optional element involves changing the power level of the continuous wave transmitted and received during the creation of the cryptographic key. At block 328, a second optional element involves selecting only symbols having magnitudes greater than a threshold in order to reduce the impact of low-level noise.

With respect to using different power levels, although the light beam incident on the photodetector 206 during key generation is an unmodulated continuous wave signal, the optical signal may have different power levels at different times depending on the protocol implemented between the optical transceivers 210 and 250. This is advantageous for the creation of cryptographic keys, because the optical signal may have different means and variances at different power levels, thus yielding different sampled and quantized symbols. In one embodiment, the power level used at a particular time is determined in response to a pseudo-random number (PN) generator 226. In this embodiment, both optical transceiver 210 and optical transceiver 250 have corresponding PN generators, which may be implemented, for example, using respective linear feedback shift registers. The common seed value may be used at the beginning of the cryptographic key creation mode to operate the corresponding PN generators 226 and 276. Thus, both PN generators 226 and 276 produce the same pseudo-random number sequence. When each optical transceiver 210 or 250 determines that a new power level is to be used (e.g., after a predetermined number of samples have been transmitted and/or received), the optical transceiver may obtain a next pseudo-random number from generator 226 or 276. The optical transceiver 250 uses the pseudo-random number to determine the power level of the continuous beam provided to the optical transceiver 210 based on the current pseudo-random number (e.g., based on two or three Most Significant Bits (MSBs) of the pseudo-random number). The optical transceiver 210 then knows the power level of the light beam received via the optical channel 230 based on the same MSB of the pseudo-random number generated by the PN generator 226.

The selection of quantized samples with an amplitude greater than the threshold at block 328 may be accomplished by filtering the quantized samples provided by the sampler/ADC 208 to eliminate samples having a value less than the threshold. Block 328 may interact with block 324 such that the threshold used may change as the power level of the received beam changes. Alternatively, the threshold may remain the same regardless of the power level of the received light beam.

At block 324, process 320 optionally determines a new power level of the signal received from optical transceiver 250. In block 326, the received signal is sampled and quantized to generate N quantized samples. As described above, the ADC used in the sampler/ADC 208 may generate a 16-bit digitized sample value. An ADC (not shown separately) of the sampler/ADC 208 may produce either linearly quantized samples or non-linearly quantized samples, with more quantization levels being assigned to higher value samples.

When process 320 includes optional block 328, the N quantized samples may be processed to select only quantized samples having a value greater than a threshold value, or to select only the more significant bits of the quantized sample value to provide an output symbol value. The threshold may be a fixed value or, when the process includes optional block 324, the threshold may change as the power level changes. Thresholding may be achieved, for example, by selecting only certain bits of the digitized sample values. In one example, each digitized sample value has an I bit, and thresholding selects the K Most Significant Bits (MSBs) of each digitized value to form K bit symbols. In the case where the range of values occupied by the digitized sample values is such that J MSBs are expected to be zero, thresholding may include deleting J MSBs of each digitized sample value before K MSBs are selected. For example, when at low power levels, where the photodetector 206 produces an electrical signal in the range of 0 to 2V, and the sampler/ADC 208 produces a 16-bit digitized value (i=16), which ranges from 0 to 16V, the block 328 may delete the three MSBs (j=3) and the three Least Significant Bits (LSBs) to provide a 10-bit symbol value (k=10).

At higher power levels, for example, when the photodetector 206 generates an electrical signal ranging from 0 to 16V, the block 328 may delete the six LSBs of each sample to still generate a 10 bit symbol. At block 330, the process 320 determines whether M symbols have been obtained. If it has not, process 320 transfers control to block 324 or 326 to obtain N more quantized samples. When M symbols are obtained at block 330, block 332 creates a cryptographic key from the M symbols.

The numbers N and M depend on the desired size of the cryptographic key, which in turn depends on the amount of data to be encrypted. For example, to create a 1024-bit cryptographic key, process 320 may need to generate 103 10-bit symbols from quantized samples. In the example shown in fig. 3B, N may have a value of 10 or greater, and M may have a value of 110, producing a desired number of symbols through at least 11 iterations of the loop of process 320. In another embodiment, the sample size may be 10 bits, N may be 1, and M may be 13, e.g., to create a 128 bit DES encryption key.

Fig. 3C is a flow chart illustrating an exemplary process 350 performed by optical transceiver 210, wherein both optical transceivers 210 and 250 simultaneously create a cryptographic key. Using this process, the optical transceivers 210 and 250 alternately transmit and receive continuous wave signals during respective first and second optical frame times. At block 352, the optical transceiver 210 determines a new power level based on, for example, two or three MSBs of the next pseudorandom number from the PN generator 226. At block 354, the processor 212 of the optical transceiver 210 controls the optical coupler 204 to direct the light beam from the optical channel to the photodetector 206. The sampler/ADC 208 then generates N quantized samples during the time that the beam from the optical channel 230 is directed to the photodetector 206. In block 358, the processor 212 optionally selects quantized samples based on their relationship to a threshold.

After block 358, the system shown in fig. 2 switches to the creation of a cryptographic key by the optical transceiver 250. At block 360, the processor 212 controls the optical coupler 204 to direct the light beam 222 from the light source 220 to direct the light beam 222 to the optical channel 230. At block 362, the processor 212 may also control the light source 220 to provide the light beam 222 at the power level determined in block 352. After block 360 and optionally after block 362, the processor 212 activates the light source 222 to transmit a continuous wave optical signal to the optical channel 230 for a time sufficient for the optical transceiver 250 to generate N quantized samples in block 364. During this time, the optical transceiver 250 performs the operations described above with reference to blocks 352-358 to generate N quantized sample values. The process continues with each of the optical transceivers 210 and 250 alternately generating N quantized sample values and converting the sample values to symbols until each of the optical transceivers 210 and 250 has acquired M symbols. Before M symbols have been obtained at block 366, process 350 branches to block 352 or block 354 to allow optical transceivers 210 and 250 to each obtain the next N quantized samples. When M symbols have been obtained at block 366, process 350 executes block 368 to generate an encryption key from the M symbols.

Fig. 4A is a flow chart illustrating an exemplary process 400 of directly creating an encryption key from M symbols generated as described above with reference to fig. 3A and 3B. At block 410, the process 400 formats the M symbols as a cryptographic key. This may require concatenating the binary values represented by the M symbols and deleting the binary bits to achieve the required key length. For example, when the desired encryption key is a 128-bit DES key, block 410 may concatenate the 13 10-bit symbols and delete the last two bits of the concatenated result to produce the 128-bit key. To ensure that the same key is created by both optical transceivers 210 and 250, it is desirable to process the M symbols using a common method to generate an encryption key. At block 412, the process 400 stores the encryption key in the memory 214 or 264.

Fig. 4B is a flow chart illustrating an alternative process 420 for creating a cryptographic key using an ECC decoder. At block 422, the processor 212 or 262 concatenates the M symbols generated as described above with reference to fig. 3A and 3B and applies the resulting value to the ECC decoder. In an exemplary embodiment, the ECC decoder may be a Reed-Solomon decoder implemented in software by the optical transceivers 210 and 250. As described above, the ECC decoder may implement a many-to-one mapping in which one of a set of encryption keys is provided in response to each of several concatenated sample values. The mapping may project concatenated symbol values onto the cryptographic key, where the concatenated symbol values differ from the cryptographic key in, for example, 1, 2, 3, or more bit positions. After obtaining the cryptographic key at block 424, process 420 stores the cryptographic key in memory 214 or 264.

The above-described embodiments operate in a network configuration such as that shown in fig. 1A, where a first optical transceiver 102 is coupled to a second optical transceiver 104 via an optical channel 106 that uses a single optical channel. As shown in fig. 1B, when one or more repeaters 158, 162 are present in the optical path between the first optical transceiver 152 and the second optical transceiver 154, it may be more difficult to implement a reciprocal path between the first optical transceiver 152 and the second optical transceiver 154. Fig. 5 is a flow chart describing a cryptographic key creation process 500 that may be used in a network such as that shown in fig. 1B. The process 500 uses the channel 164 between the first optical transceiver 152 and the second optical transceiver 154 as a full duplex channel that simultaneously transmits optical signals in both directions. In this process, an optical signal transmitted from the first optical transceiver 152 is reflected by the second optical transceiver 154 and then sampled and digitized at the first optical transceiver 152 to create a cryptographic key for use by the first optical transceiver 152. Similarly, an optical signal transmitted from the second optical transceiver 154 is reflected by the first optical transceiver 152 and then sampled and digitized at the second optical transceiver 154 to create a corresponding cryptographic key used by the second optical transceiver 154. Although not shown in fig. 5, it is contemplated that process 500 may use beams having different power levels and may interleave the transmission and sampling of optical signals by first transceiver 154 with the transmission and sampling of optical signals at second transceiver 156.

Fig. 5 is described in terms of optical transceivers 210 and 250 shown in fig. 2 for purposes of describing fig. 5, assuming that optical path 230 between transceivers 210 and 250 includes one or more repeaters (not shown in fig. 2). With respect to transceiver 210, prior to initiating process 500, optical coupler 254 of optical transceiver 250 is configured to direct light from optical channel 230 to mirror element 274. Then, at block 510, the process 500 activates the light source 220, and at block 512, the optical coupler 204 is controlled to direct light from the optical channel 230 to the photodetector 206, and simultaneously direct the light beam 222 from the light source 220 to the optical channel 230. This causes the light beam 222 to reflect off of the mirror element 274 of the transceiver 250 through the optical channel 230 and then be received and directed to the photodetector 206 of the optical transceiver 210.

At block 514, the optical signal incident on the photodetector 206 is sampled and quantized by the sampler/ADC 208, as described above, and the resulting quantized samples are provided to the processor 212. The processor may filter the samples at block 516 to remove quantized samples having a magnitude less than a threshold, for example, by deleting the less significant bits of the samples and possibly the more significant bits of the samples as described above, to generate symbols corresponding to the quantized samples. Also as described above, process 500 may delete a zero value symbol. At block 518, the process 500 may then create and store a cryptographic key from the accumulated samples as described above with reference to fig. 3A-4B. At block 520, after generating and storing the cryptographic key, the optical transceiver 210 may control the optical coupler 204 to direct the optical channel 230 to the mirror element 224. The optical transceiver 210 may then maintain this configuration for a sufficient amount of time for the optical transceiver 250 to create its cryptographic key.

The optical transceiver 210 then controls the optical coupler 204 to direct the optical beam 222 to the optical channel 230 at block 522, and encrypts the known data set using the created encryption password and transmits to the optical transceiver 250 at block 254. The known data set may be part of a protocol between the optical transceivers 210 and 250. As described below, which is used to determine whether the cryptographic keys of the two optical transceivers 210 and 250 match. As described above, the optical transceiver 210 may then wait for an acknowledgement of receipt, or may receive an encrypted known data set from the optical transceiver 250. When the optical transceiver 210 does not receive an acknowledgement or is unable to decrypt the known data set, the process 500 may be restarted to create another encryption key.

Fig. 6A and 6B are graphs of signal power versus time illustrating sampling operations performed in exemplary optical transceivers 210 and 250. Fig. 6A and 6B illustrate exemplary sampling of various optical signals received at transceiver 210 of fig. 2. SA (SA) ₁ 、SA ₂ 、SA ₃ 、SA ₄ 、SA ₅ 、SA ₆ 、SA ₇ 、...、SA _N-1 Sum SA _N Is a quantized sample generated by the sampler/ADC 208 at intervals shown along the horizontal time axis. At the corresponding sample SA ₁ 、SA ₂ 、SA ₃ 、SA ₅ 、SA ₆ The third, and SA _N Under the mark SY ₁ 、SY ₂ 、SY ₃ 、SY ₄ 、SY ₅ 、SY ₆ The term, and SY _N-2 Indicating the corresponding N-2 symbols generated from the N quantized samples. As described above, in one example, the quantized samples may be 16-bit values, and the symbols may be 10-bit values derived from corresponding ones of the quantized samples.

Each quantized sample is a bit string that indicates the value of the sampled optical power level indicated by the height of the quantized sample, as shown by the vertical power axis. As described above, the power level is related to the number of photons incident on the photodetector 206 during the integration interval (e.g., 1ns to 50 ns). The relative heights of the quantized samples are exaggerated in fig. 6A and 6B to illustrate the operation of the embodiments. Alternatively, the relative heights of the quantized samples may represent the ADC of the sampler/ADC 208 that implements a nonlinear transfer function that assigns more quantized levels to higher power levels than lower power levels, thereby enhancing the differences between higher power samples while reducing the differences between lower power samples.

In the scenario illustrated in fig. 6A, the sampler/ADC 208 of the optical transceiver 210 receives the optical signal transmitted by the optical transceiver 250 at a single power level. The horizontal line T represents a threshold value. As described above, the transceiver may ignore quantized samples having a value less than the threshold T when generating output symbols that are used to create cryptographic keys. As shown in fig. 6A, sample SA ₄ Sum SA _N-1 Has a value less than the threshold T and is ignored such that the processor 212 of the optical transceiver 210 generates the symbol SY ₁ 、SY ₂ 、SY ₃ 、SY ₄ 、SY ₅ 、SY ₆ And SY _N-2 Corresponding to each sample SA ₁ 、SA ₂ 、SA ₃ 、SA ₅ 、SA ₆ 、SA ₇ Sum SA _N 。

The scenario shown in fig. 6B illustrates an example in which the power level of the continuous wave optical signal provided by optical transceiver 250 varies between power level 1 and power level 2. Quantized sample SA ₁ 、SA ₂ 、SA ₃ Sum SA ₄ Representing samples received at power level 1, sample SA ₅ 、SA ₇ 、...、SA _N-1 Sum SA _N Representing samples received at power level 2, where power level 2 is lower than power level 1. The embodiment illustrated by fig. 6B shows two thresholds T1 and T2. In this embodiment, T1 is used for quantized sample SA ₁ 、SA ₂ 、SA ₃ Sum SA ₄ While T2 is used for quantized sample SA ₅ 、SA ₆ 、SA ₇ 、...、SA _N-1 Sum SA _N . As shown in fig. 6B, quantized sample SA ₄ Less than T1, and quantized sample SA ₆ Sum SA _N-1 Less than T2. Thus, these samples are ignored and no corresponding symbol is generated. Thus (2)In the scenario shown in fig. 6B, the processor 212 of the optical transceiver 210 is based on N quantized samples SA ₁ 、SA ₂ 、SA ₃ 、SA ₄ 、SA ₅ 、SA ₆ 、SA ₇ 、...、SA _N-1 Sum SA _N Generating N-3 symbols SY ₁ 、SY ₂ 、SY ₃ 、SY ₄ 、SY ₅ The term, and SY _N-3 . As described above, when generating symbols from quantized samples, the processor 212 may subtract a threshold from the quantized samples (e.g., delete LSBs corresponding to the threshold). Further, the processor 212 may delete the MSB of the quantized symbol that is expected to be a zero value based on the current power level.

The exemplary embodiments disclosed herein may be described in the general context of processor-executable code or instructions being stored on a memory that may include one or more computer-readable storage media (e.g., tangible, non-transitory computer-readable storage media, such as memory 214 or 264). It should be readily understood that the terms "computer-readable storage medium" or "non-transitory computer-readable medium" include media for storing data, code, and program instructions, such as memories 214, 264, and do not include portions of the media for storing the temporarily propagated or modulated data communication signals.

Example

Example 1 is a cryptographic key generator for a first optical transceiver, comprising: a photodetector configured to receive the first light beam from the optical channel; a memory including program instructions; a processor coupled to the memory and the photodetector, the processor configured by the program instructions to: receiving a signal from the photodetector responsive to the first light beam; sampling the signal from the photodetector during a first plurality of intervals to generate respective samples representing a respective number of photons incident on the photodetector during each interval of the first plurality of intervals; quantizing the samples to generate a plurality of digital values; and creating a cryptographic key from the plurality of digital values.

In example 2, the subject matter of example 1 includes: wherein the program instructions configure the processor to: a digital value of the plurality of digital values having a magnitude greater than a threshold value is selected for creation of the cryptographic key.

In example 3, the subject matter of examples 1-2 includes: wherein the digital value is an I-bit digital value, wherein I is an integer, and program instructions configure the processor to: selecting K bits of each of the I-bit digital values, where K is an integer less than I, to generate a plurality of K-bit symbols; deleting symbols with zero values in the K-bit symbols to provide a set of K-bit symbols of non-zero values; and concatenating the non-zero value K-bit symbols to create the cryptographic key.

In example 4, the subject matter of example 3 includes: wherein program instructions configure the processor to: applying the concatenated value to an Error Correction Code (ECC) decoder to generate an output value; and storing the output value as the cryptographic key in the memory.

In example 5, the subject matter of examples 3-4 include: wherein the K bits are K Most Significant Bits (MSBs) of the I-bit digital value.

In example 6, the subject matter of examples 3-5 include: wherein the I-bit digital values are expected to have a range of values such that each I-bit digital value has J zero-valued Most Significant Bits (MSBs), where J is an integer less than I and j+k is less than I, and the program instructions cause the processor to: deleting J MSBs of each of the I bit values to form an I-J bit digital value; and selecting K MSBs of each of the I-J bit digital values to generate a K-bit symbol.

In example 7, the subject matter of examples 1-6 include: wherein the first beam is a continuous wave beam.

In example 8, the subject matter of examples 1-7 include: wherein during a predetermined interval of the first plurality of intervals, the first light beams respectively have different power levels, and the program instructions configure the processor to: selecting a respective threshold for use during each of the predetermined intervals; selecting a digital value of the plurality of digital values having an amplitude greater than the selected threshold value during each predetermined interval; and creating the cryptographic key from the selected digital value.

In example 9, the subject matter of examples 1-8 include: wherein the first optical transceiver further comprises: a light source configured to generate a second light beam; and an optical coupler configured to selectively direct the second light beam from the light source to the optical channel and to direct the first light beam from the optical channel to the photodetector; and the program instructions further configure the processor of the cryptographic key generator to control the optical coupler and the light source to: directing the first light beam from the optical channel to the photodetector during the first plurality of intervals; and directing the second light beam from the light source to the optical channel during a second plurality of intervals different from the first plurality of intervals.

In example 10, the subject matter of example 9 includes: wherein the second plurality of intervals occurs after the first plurality of intervals.

In example 11, the subject matter of examples 9-10 include: wherein the second plurality of intervals is interleaved with the first plurality of intervals.

In example 12, the subject matter of examples 9-11 include: wherein the first plurality of intervals occurs during a first optical frame time and the second plurality of intervals occurs during a second optical frame time; and the program instructions further configure the processor to: encrypting data to be transmitted via the optical channel using the created cryptographic key; controlling the light source to modulate the second light beam according to the encrypted data during a third interval different from the first optical frame time and the second optical frame time; controlling the optical coupler to direct the second light beam to the optical channel during the third interval and to direct the first light beam from the optical channel to the photodetector during a fourth interval, wherein the fourth interval is different from the third interval and the first and second optical frame times; and decrypting the digital value generated by the processor in response to the second light beam incident on the photodetector using the cryptographic key during the fourth interval.

In example 13, the topics of topics 1-12 include: a light source configured to generate a second light beam; a reflective element; and an optical coupler configured to: selectively directing the first light beam from the optical channel to the reflective element or the first light beam to the photodetector, and directing the second light beam to the optical channel; wherein the instructions further configure the processor to control the optical coupler and the light source to: directing the second light beam to the optical channel and the first light beam to the photodetector during the first plurality of intervals; and directing the first light beam to the reflective element during a second plurality of intervals different from the first plurality of intervals.

Example 14 is a method for generating a cryptographic key in an optical transceiver, the method comprising: receiving a signal from a photodetector of the optical transceiver in response to a light beam incident on the photodetector; sampling the signal from the photodetector during a plurality of intervals to generate a respective sample representative of a respective number of photons incident on the photodetector during each of the plurality of intervals; quantizing the samples to generate a plurality of digital values; and creating the cryptographic key from the plurality of digital values.

In example 15, the subject matter of example 14 includes: and selecting a digital value with the amplitude larger than a threshold value from the digital values for creating the cryptographic key.

In example 16, the subject matter of example 15 includes: selected ones of the plurality of digital values are concatenated and the concatenated values are applied to an Error Correction Code (ECC) decoder to create the cryptographic key.

In example 17, the subject matter of examples 14-16 include: wherein the light beam is a continuous wave light beam.

In example 18, the subject matter of example limbs 14-17 includes: wherein the light beams have different power levels during predetermined ones of the plurality of intervals, respectively, and the method further comprises: selecting a respective threshold for use during each predetermined interval; generating the cryptographic key includes: a digital value of the plurality of digital values during each predetermined interval having an amplitude greater than the selected threshold value is selected.

Example 19 is an apparatus for generating a cryptographic code in an optical transceiver, comprising: means for receiving a plurality of signals representative of a respective number of photons of the optical beam received by the optical transceiver during each of a plurality of intervals; means for generating respective digital values representing the received plurality of signals; means for selecting a digital value of the plurality of digital values having an amplitude greater than a threshold value; and means for generating the cryptographic key from the selected one of the plurality of digital values.

In example 20, the subject matter of example 19 includes: wherein the light beams have different power levels during predetermined ones of the plurality of intervals, respectively, and the apparatus further comprises: means for selecting a respective threshold value for use during each predetermined interval; and the means for generating the cryptographic key comprises: means for selecting a digital value of the plurality of digital values during each predetermined interval having an amplitude greater than the selected threshold value.

Example 21 is at least one machine-readable medium comprising instructions that, when executed by processing circuitry, cause the processing circuitry to perform operations for implementing any of examples 1-20.

Example 22 is an apparatus comprising means for implementing any of examples 1-20.

Example 23 is a system to implement any of examples 1-20.

Example 24 is the method of any of examples 1-20.

What has been described above includes examples of the claimed subject matter. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the claimed subject matter, but one of ordinary skill in the art may recognize that many further combinations and permutations of the claimed subject matter are possible. Accordingly, the claimed subject matter is intended to embrace all such alterations, modifications and variations that fall within the scope of the appended claims.

In particular regard to the various functions performed by the above described components, devices, circuits, systems and the like, the terms used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component, e.g., that is functionally equivalent, even though not structurally equivalent to the disclosed structure, which performs the function in the herein illustrated exemplary aspects of the claimed subject matter. In this regard, it will also be recognized that the disclosed exemplary embodiments and implementations include a system as well as a computer-readable storage medium having computer-executable instructions for performing the acts and events of the various methods of the claimed subject matter.

There are numerous ways to implement the claimed subject matter, e.g., an appropriate API, tool kit, driver code, operating system, control, stand-alone or downloadable software object, etc., that enable applications and services to use the techniques described herein. The claimed subject matter contemplates use from the standpoint of an API (or other software object) as well as from the standpoint of a software or hardware object that operates in accordance with the techniques set forth herein. Thus, various implementations of the claimed subject matter described herein may have aspects that are wholly in hardware, partly in hardware and partly in software, as well as software.

The foregoing exemplary system has been described with respect to interactions between several components. It will be understood that such systems and components can include those components or specified sub-components, some of the specified components or sub-components, and additional components, in accordance with various permutations and combinations described above. Sub-components may also be implemented as components communicatively coupled with other components rather than included in parent components (hierarchical).

In addition, it should be noted that one or more components may be combined into a single component providing aggregate functionality or divided into several separate sub-components, and any one or more intermediate layers, such as a management layer, may be provided to communicatively couple to such sub-components in order to provide integrated functionality. Any of the components described herein may also interact with one or more other components not specifically described herein but generally known by those of skill in the art.

Furthermore, while a particular feature of the claimed subject matter may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms "includes," "including," "has," "contains," variants thereof, and other similar words are used in either the detailed description or the claims, these terms are intended to be inclusive in a manner similar to the term "comprising" as an open transition word without precluding any additional or other elements.

Claims

1. A cryptographic key generator for a first optical transceiver, comprising:

a photodetector configured to receive the first light beam from the optical channel without modulation;

a memory including program instructions;

a processor coupled to the memory and the photodetector, the processor configured by the program instructions to:

receiving a signal from the photodetector responsive to the first light beam;

sampling the signal from the photodetector during a first plurality of intervals to generate respective samples representative of a respective number of photons incident on the photodetector during each interval of the first plurality of intervals, wherein a characteristic of the optical channel results in a variation between the respective samples;

quantizing the samples to generate a plurality of digital values; and

the cryptographic key is created from the plurality of digital values.

2. The cryptographic key generator of claim 1, wherein the program instructions configure the processor to: a digital value of the plurality of digital values having a magnitude greater than a threshold value is selected for creation of the cryptographic key.

3. The cryptographic key generator of claim 1, wherein the digital value is an I-bit digital value, wherein I is an integer, and program instructions configure the processor to:

Selecting K bits of each of the I-bit digital values, where K is an integer less than I, to generate a plurality of K-bit symbols;

deleting K-bit symbols with a value of zero in the K-bit symbols to provide a set of K-bit symbols of non-zero values; and

concatenating the non-zero value K-bit symbols to create the cryptographic key.

4. The cryptographic key generator of claim 3, wherein program instructions configure the processor to:

applying the concatenated value to an Error Correction Code (ECC) decoder to generate an output value; and

the output value is stored in the memory as the cryptographic key.

5. A cryptographic key generator according to claim 3, wherein the K bits are K Most Significant Bits (MSBs) of the I-bit digital value.

6. A cryptographic key generator according to claim 3, wherein the I-bit digital values are expected to have a range of values such that each I-bit digital value has J zero-valued Most Significant Bits (MSBs), where J is an integer less than I and j+k is less than I, and the program instructions cause the processor to:

deleting J MSBs of each of the I-bit values to form an I-J-bit digital value; and

K MSBs of each of the I-J-bit digital values are selected to generate the K-bit symbol.

7. The cryptographic key generator of claim 1, further wherein the first light beams have different power levels, respectively, during predetermined ones of the first plurality of intervals, and the program instructions configure the processor to:

selecting a respective threshold for use during each of the predetermined intervals;

selecting a digital value of the plurality of digital values during each predetermined interval having an amplitude greater than the selected threshold value; and

the cryptographic key is created from the selected digital value.

8. The cryptographic key generator of claim 1, wherein:

the first optical transceiver further comprises:

a light source configured to generate a second light beam; and

an optical coupler configured to selectively direct the second light beam from the light source to the optical channel and to direct the first light beam from the optical channel to the photodetector; and

the program instructions further configure the processor of the cryptographic key generator to control the optical coupler and the light source to:

Directing the first light beam from the optical channel to the photodetector during the first plurality of intervals; and

the second light beam from the light source is directed to the optical channel during a second plurality of intervals different from the first plurality of intervals.

9. The cryptographic key generator of claim 8, wherein:

the first plurality of intervals occurs during a first optical frame time and the second plurality of intervals occurs during a second optical frame time; and

the program instructions further configure the processor to:

encrypting data to be transmitted via the optical channel using the created cryptographic key;

controlling the light source to modulate the second light beam according to encrypted data during a third interval different from the first optical frame time and the second optical frame time;

controlling the optical coupler to direct the second light beam to the optical channel during the third interval and to direct the first light beam from the optical channel to the photodetector during a fourth interval, wherein the fourth interval is different from the third interval and the first and second optical frame times; and

During the fourth interval, decrypting the digital value generated by the processor in response to the second light beam incident on the photodetector using the cryptographic key.

10. The cryptographic key generator of claim 1, further comprising:

a light source configured to generate a second light beam;

a reflective element; and

an optical coupler configured to:

selectively directing the first light beam from the optical channel to the reflective element or to the photodetector, and

directing the second light beam to the optical channel;

wherein the instructions further configure the processor to control the optical coupler and the light source to:

directing the second light beam to the optical channel and the first light beam to the photodetector during the first plurality of intervals; and

the first light beam is directed to the reflective element during a second plurality of intervals different from the first plurality of intervals.

11. A method for generating a cryptographic key in an optical transceiver, the method comprising:

receiving a signal from a photodetector of the optical transceiver in response to an unmodulated optical beam incident on the photodetector, the optical beam received from an optical channel;

Sampling the signal from the photodetector during a plurality of intervals to generate a respective sample representative of a respective number of photons incident on the photodetector during each of the plurality of intervals, wherein a characteristic of the optical channel results in a change between the respective samples;

quantizing the samples to generate a plurality of digital values; and

the cryptographic key is created from the plurality of digital values.

12. The method of claim 11, further comprising: a digital value of the plurality of digital values having a magnitude greater than a threshold value is selected for creation of the cryptographic key.

13. The method of claim 12, further comprising concatenating the selected ones of the plurality of digital values and applying the concatenated values to an Error Correction Code (ECC) decoder to create the cryptographic key.

14. The method of claim 11, further wherein the light beams have different power levels during predetermined ones of the plurality of intervals, respectively, and the method further comprises:

selecting a respective threshold for use during each predetermined interval; and

generating the cryptographic key includes: a digital value of the plurality of digital values during each predetermined interval having an amplitude greater than the selected threshold value is selected.

15. An apparatus for generating a cryptographic key in an optical transceiver, comprising:

means for receiving a plurality of signals representing a respective number of photons of an unmodulated optical beam received by the optical transceiver from an optical channel during each of a plurality of intervals, wherein,

the characteristics of the optical channel cause variations between the plurality of signals;

means for generating respective digital values representing the received plurality of signals;

means for selecting a digital value of the plurality of digital values having an amplitude greater than a threshold value; and

and means for generating the cryptographic key from the selected one of the plurality of digital values.