High-speed optical line protected from eavesdropping by quantum noise

FIELD: physics.

SUBSTANCE: received power level of an optical signal in a link is monitored and matched with the transmitting side, selecting it to be maximally low, comparable to the level of optical quantum noise at the receiving side and where it is still possible to recover lost information bits while minimising optical losses in the optical line; a key for decrypting a bit data packet contained in the packet itself can vary from packet to packet and a cryptographic algorithm is selected such that decryption is impossible if a bit is lost from a data packet. The optical link comprises: a transmitter with an actuator, a receiving optical amplifier, a photoelectronic converter with an output narrow-band filter.

EFFECT: improved robustness against unauthorised information access by combining high data transmission rate with maximally low power of quantum bits of an encoded signal.

14 cl, 3 dwg

The technical field

The invention relates to the field of telecommunications, and in particular to optical communication lines for better security, operating at extremely high speeds the transfer of information using quantum effects to protect the information from possible interception.

Prior art

Less than half a century was required to quantum cryptography has gone from idea to implementation in a commercial system for quantum key distribution. Current equipment allows to distribute keys via the quantum channel at a distance greater than 100 km of Main consumers of systems of quantum cryptography in the first act of the Ministry of defense, Ministry of foreign Affairs and major trade associations. Currently the high cost of quantum systems key distribution limits their mass application for the organization of confidential communication between small and medium firms and individuals.

In the fiber-optic lines, the process of communication using quantum cryptography is performed by physical means and is based on registration of counting the number of photons. Register counting the number of photons in the line fiber in the presence of a proper quantum noise - 1 photon per second in the frequency band 1 Hz, on one degree of freedom for polarized radiation in the fiber. Check-photon avalanche photodiode in this case is carried out at low transmission speeds of the order of 1 Mbit/s is Considered that focusing on quantum phenomena, you may want to design and create such a communication system, which can always detect listening. This is ensured by the fact that the attempt measurement of related parameters in a quantum system makes it a violation, destroying the initial quantum state of the photons, and therefore, the level of noise in the channel of the legitimate users can recognize the degree of activity of the interceptor.

Researchers from northwestern University (Evanston, Illinois) demonstrated a technology that allows for a short distance, an encrypted message with a data rate of 250 Mbit/s [1, 2]. Scientists have proposed a method of quantum coding the data itself, and not just one key. In this model takes into account the angle of polarization of each transmitted photon, therefore, any attempt to decode the message leads to the noise channel, that every decoding becomes impossible. Researchers promise that the model of the next generation will be able to work practically on the main Internet speed of 2.5 Gbit/s According to one of the developers, Professor Prema Kum is RA (Prem Kumar) "no one has managed to perform quantum encryption at such speeds" (2003-2005). Scientists have already received several patents for his inventions and are now working together with its industrial partners Telcordia Technologies and BBN Technologies on further improvement of the system.

Known methods of data transmission via optical fiber networks using quantum cryptography, for example: US 20040109564 A1, HIGH-RATE QUANTUM KEY DISTRIBUTION SCHEME RELYING ON CONTINUOSLY PHASE AND AMPLITUDE-MODULATED COHERENT LIGHT PULSES, Cerf et al., in which to transmit secret information using quantum communication channel, and for the exchange of service data using the open public communication channel. However, the transmission rate of the quantum channel is low, and test the transmission of the secret key was about 1.7 Mbit/s System is vulnerable to decrypt the information with the interception of a secret key.

There is a system for transmission of optical data with the quantum signal coding: US 2009268901 (Al), CONTINUOUS VARIABLE QUANTUM ENCRYPTION KEY DISTRIBUTION SYSTEM, Lodewyck et al., which was proposed in order to ensure maximum compatibility with your existing long-distance optical links. However, because the communication line extended, to fight with quantum noise and passing it a sequence of photon pulses have to increase their number, i.e. the power light because of line loss on the receiving side, more precisely, to increase the ratio of signal to noise ratio (OSNR). Utopistic to in the transmitting device, in line there is a large enough signal, so that part of it could be branched for listening devices. So a potential unauthorized access to information. In addition, the task of the listening part is much easier, since the transmission data using the laws of quantum mechanics for counting the number of photons occurs at low frequencies.

There are optic line, ensuring error-free data transmission between two parties. Their goal is to accurately convey coded information, for example: WO 2007035599 (A2), METHOD AND SYSTEM FOR CONTROL LOOP RESPONSE TIME OPTIMIZATION, Fedyakin et al. To do this, use redundant coding, FEC coding (Forward Error Correction) and a consistent configuration of the optical transmitter and receiver for reliable error-free reception and FEC-decoding signal. Reliable reception of data creates favorable conditions for interception of information in an unauthorized connection to the fiber line. In such lines of communication possible interception of data.

There is a way coherent data transmission OPTICAL ORTHOGONAL FREQUENCY DIVISION DEMULTIPLEXED COMMUNICATIONS WITH COHERENT DETECTION, US 20080159758 Al, Shpantzer et al., in which use coherent detection of the signal on the receiving side. Coherence in the data receiving means in the optical p is jemnice registers not only the amplitude of the input signal, but also the phase. Coherent reception is carried out by mixing the received signal with the additional radiation of the laser in the receiver. This laser plays the role of the local oscillator. The sensor components are allocated proportional to the square of the module of the optical field of the received signal and the local oscillator. They are separated by electronics. Information about the phase is contained in the interference term, formed by the product of the fields of the signal and oscillator. To increase the overall speed of data transmission using orthogonal polarized optical signal, and for sustained data transfer method used for error correction. The level of the transmitted optical signal in this way is sufficiently high to ensure maximum reliability of the data and in the event of accidental loss to 1 dB, the system will function and, therefore, unauthorized human intervention in the line will not be seen. This means that conditions are favorable for good reception data at the receiving side, and for the listening party. This is the main drawback of the proposed method.

The above data transmission systems operating in the mode of account of individual photons and, as a consequence, may not work at speeds above 1Gbit/s is shown above disadvantages lacks the following proposed fiber-optic communication line is highly sensitive due to the refusal of the counting mode of the individual photons and the system configuration at the maximum rate of data transfer up to 100 Gbit/s and above. The power transmitting device selects the minimum at which output per 1 bit of information commensurate with the level of quantum noise in the line in the corresponding transmission speed bandwidth.

Description of the invention

The purpose of the present invention is to offer high-speed fiber-optic communication line increased resistance to listening, working at extremely low optical power signal commensurate with the background of quantum noise in a fiber line with the data protection cryptographic encryption algorithm, which satises the avalanche criterion (a Term introduced by Pasteles [3]), using the redundant encoding and decoding of the signal.

Optical data transmission system shown in figure 1. Information package 1 is fed to the input of encoder 2 (cryptosystem), which performs encryption (cryptographic transformation of data on the basis of avalanche algorithm and key). Then you enter error-correcting redundant coding of data - the so-called FEC-coding (Forward Error Correction) using FEC encoding device 3. Then the signal is transmitted in an optical communication line using the optical transmitter 4, for example, a semiconductor DFB laser diode with a narrow spectral line. N the necessary optical power set of tunable optical attenuator 5 (VOA). At the receiving side, the optical signal from the optical fiber 6, is amplified, for example, erbium-doped fiber amplifier 7 (EDFA). The output of the amplifier is set to a narrow-band optical filter 8, the emitting spectrum of the transmitted signal and filter the parasitic spontaneous superluminescence output from the EDFA. After the filter the optical signal is recorded a photodetector 9 - photoelectric Converter and fed to the input of the FEC-decoding device 10. Next, the data are interpreted on deshifriruyut device 11, and its output received recovered information signal 12.

The principle of operation

High secret conditions for the transfer of coded information are provided by the mode selection optical system near the level of quantum noise. Any external influence on the optical path in order to obtain access to the transmitted information leads to a weakening of the power level at the input of the optical amplifier receiving side, therefore, degrades the optical signal-to-noise ratio (OSNR) and errors occur in the received data. When encryption is used with a cryptographic algorithm that satises the avalanche criterion, the presence of at least one error in the information package makes it impossible for its interpretation prinimaya the party. Therefore, there will be probable the fact that outside interference in secret communication line. On the other hand, if the optical power level that branch of the attacker is small by any stretch of the line, then this action is:

1 - will not lead to interruption of transmission on the main path,

2 - due to the smallness of the level of the branched power, it is absolutely not enough to decode the signal by an attacker.

Obviously, the less optical loss in the line, the better it is protected from eavesdropping and the easier it is to establish the fact of intervention on the level drop signal on the receiving side.

The use of additional FEC (EFEC) coding is caused for the following reasons. As shown in figure 2 [4], for a transfer rate of 2.5 GB/s with the same error rate (BER) EFEC-coding (Enhanced FEC) is winning by about 8.5 dB receiver sensitivity compared with the system without excessive coding (curve 21 is obtained without excessive coding, curve 22 is received with excessive EFEC-encoding). Thus, due to this it is possible to reduce the optical power at the receiver, which increases security and makes it a secret. Note that the dependence of the BER from OSNR has a large slope in the case of EFEC compared with the FEC. This leads to the fact that at very small decrease in optical powerfully the tee on the receiver (for example, 0.5 dB in the field OSNR=1.5 dB) is a sharp increase in the likelihood of errors (10^-13up to 10^-4).

Configuring optical power at the input of the optical amplifier 7, Figure 1, the receiving side is performed on the transmission side at the expense of the tunable optical attenuator 5. The working point along the axis of the OSNR is chosen close to the value of 1.5 dB, which guarantees error-free operation of the system in normal (without outside interference) condition. External influence on the transmission path, resulting in an additional loss of-0.5 dB OSNR is accompanied by a sharp increase in the probability of error of up to 10^-8(Figure 2). Another big loss is 1.0 dB OSNR, raise the error to the level of more than 10^-3. Thus, the system is extremely sensitive to external interference in the optical line, calling for more loss of optical power, and therefore, the dramatic increase in uncorrected reservation system errors. And the loss of at least one bit of the transmitted encrypted packet at avalanche encoding algorithm leads to a complete loss of sensitive data, which in itself is for the receiving party is a signal to interference and this notified the transferor. In other words, the receiving party is configured to extremely low signal - minimal is th OSNR, when the power of the useful optical signal commensurate with the optical noise in the line and virtually any unforeseen losses in the line will cause the loss of data and automatic termination of secret data to determine the cause of external influence. The length of the line and the stock level of the signal at the receiver are chosen from the condition that the losses in the line from the alleged interference to the receiver were significantly less than the losses in the branch line listening. Note that the attenuation of 1 dB in the optical path is equivalent to connecting optical coupler with a division ratio of 20/80% (80% optic tract, 20% of the listening device). Changing the size of the data packet, which are cryptographic conversion, you can adjust the threshold level of errors, which can recover the data. For example, increasing the batch size from 1 Kbit to 1 Mbit critical BER decreases proportionally from 10^-3up to 10^-6.

Figure 3 shows the diagram of the bidirectional transmission lines, in which transmitters and receivers are made by analogy with the system shown in figure 1.

When you encounter a critical error rate of data transmission in one of the two communication lines (Figure 3) in the direction 31-32, under which the cryptographic vos is the establishment of data is impossible due to interference of the coupler 34 is listening device 37, in the reverse direction 31'-32' on the other line is sent to the appropriate service signal informing about the failure of the transmission. The transmitter 31 stops the transmission of data starts streaming only service signal, you need to find causes of errors.

To increase the data transfer rate optical line can be arranged using both frequency sealing channels, and using orthogonally polarized optical signals. Coherent reception of optical signals minimizes optical noise in the detection signal on the receiving side, and therefore, in combination with the method of error correction makes it possible to reduce the transmit power to the maximum possible, commensurate with the level of optical noise of polarized radiation in the fiber:

~ 1 photon/s in the frequency range 1 Hz - 1^-1·Hz^-1/2. For transmission of the optical signal at the wavelength of 1550 nm, this corresponds to the energy of 1 photon of 1.25·10^-19J. With transfer rates of 100 Gbit/s quantum noise power has a value of about 10^-8W.

Dignity

In contrast to existing optical systems, quantum cryptography, the proposed model can operate on low and high transmission speeds up to 100 Gbps and above.

Sistem.pozvolte to control unauthorized access by various parameters:

- Measurement of optical power level at the output line.

Control load FEC (the number of errors corrected at the expense of redundant encoding).

Control the number of lost packets of information during cryptographic decoding key to decrypt the cryptographic package can be transmitted together with the package and can vary from package to package. In this case there is no need for additional transmission channel key. The loss of any bits in the key, and the package leads to the impossibility of recovery of the transmitted information.

When bidirectional transmission is possible introduction to the special signal pulse - time stamps for the calibration of time-of-flight of the communication area. Having received from the sender of the packet and the timestamp, the receiver returns a response about getting the label to the side of the sender. The sender measures the time delay between sending and receiving labels. This delay is fixed when the system is put into operation and in the event of a deviation of this parameter stops the transmission of classified information.

The transmission channel may be any optical fiber, both isotropic and anisotropic using coherent signal detection. Protection and heightened security line provides "the bodily level," the use of microstructure fiber, which forms a waveguide transmission channel of the optical signal substantially based on quantummechanically principles. Intervention in such a channel will inevitably lead to a significant loss of optical power. The use of a microstructure fiber will help to optimize the conditions for the passage of radiation through the fiber line, to reduce losses and to increase its protection from unauthorized access.

Thus, in the present invention include:

1. How to send encrypted data over a bidirectional fiber-optic communication lines with error correction and attenuation of the transmitted in each direction of the optical signal and amplified on the receiving side, followed by narrow-band filtering, and characterized in that:

- the level of the received power of the optical signal communication line control and choose extremely low, commensurate with the level of optical quantum noise on the receiving side, and one with which it is still possible to recover lost bits of information while minimizing the optical loss in the optical line,

- the key to decrypt the packet bit data contained in the package and can vary from package to package,

- cryptographic algorithm that satises the avalanche criterion is chosen so that when the pot is E. at least one bit of the data packet decryption was impossible,

- optical communication line has high resistance to unauthorized listening due to the transmission of data at extremely high speeds in combination with extremely low-power signal transmitting side,

where:

- encrypted data transmission is terminated by the fall of the level taken after amplification of the signal at a value ranging from 0.2 dB to 0.7 dB OSNR;

- encrypted data transmission stops if the maximum allowable level of corrected errors;

- encrypted data transmission is terminated by an unexpected change in time-of-flight communication line;

transmission is performed in an isotropic or anisotropic, or microstructure optical fiber, or combinations thereof;

- the transfer rate is selected as high as possible up to 100 Gbit/s and above in line with the length of up to 50 km;

- carry out coherent reception of an optical signal.

2. Fiber-optic communication line with encryption of data in two directions with error correction, containing for each direction cascaded optical:

transmitter with attenuator,

- receiving optical amplifier

photoelectronic Converter with an input narrowband filter

and characterized by the fact that the excessive secrecy of the communication line is achieved in R is the result, that:

- the level of the received power of the optical signal communication line control and choose extremely low, commensurate with the level of quantum noise and such, which is still possible to recover lost bits of information

- the key to decrypt the packet bit data contained in the package and can vary from package to package,

- cryptographic algorithm that satises the avalanche criterion is chosen so that with the loss of at least one bit of the data packet decryption was impossible,

optical line has a high resistance to unauthorized listening due to the transmission of data at extremely high speeds in combination with extremely low-power signal transmitting side,

in which:

- encrypted data transmission is terminated by the fall of the signal level at the input of the optical receiver at a value ranging from 0.2 dB to 0.7 dB OSNR,

- encrypted data transmission stops if the maximum allowable level of corrected errors,

- encrypted data transmission is terminated by an unexpected change in time-of-flight line,

transmission is performed in an isotropic or anisotropic, or microstructure optical fiber, or combinations thereof,

- speed transmission liberaltarians high up to 100 Gbit/s and above in line with the length of up to 50 km,

photoelectronic Converter carries out the coherent conversion of the optical signal.

Brief description of drawings

Figure 1. The scheme of data transmission in optical communication lines.

1 is transmitted unencrypted data,

2 - device encryption, encoder (cryptographer),

3 - unit redundant coding (FEC-encoder),

4 - optical transmitter (DFB laser diode),

5 - optical attenuator (VOA),

6 - fiber single-fibre line,

7 - optical amplifier

8 - optical narrow-band filter,

9 photoelectronic Converter

10 - unit redundant decoding FEC decoder

11 - device decryption decoder,

12 - received decrypted data.

Figure 2. The dependence of error rate (BER) of the optical signal-to-noise ratio (OSNR).

21 - curve error rate (BER) in the absence of redundant coding

22 - curve error rate (BER) in the presence of redundant coding, EFEC-coding (Enhanced FEC).

Figure 3. Diagram of the bidirectional communication line with a branch to listen to.

31, 31' is transmitted unencrypted data,

36, 36' optical fiber communication line,

32, 32' is received decrypted data

33, 33' - transmitter

34 - optical beamsplitter,

35, 35' - receiving device, photoelectro the hydrated Converter with an input narrowband filter

36 - fiber listening devices,

37 - listening device.

The implementation of the invention

For carrying out the invention can be used with standard 5 of the telecommunications equipment. In accordance with Figure 3 transmitting system set up on the operating point OSNR=l,5 dB. The size of the cryptographic package choose 1 Mbit. Threshold BER, which is still possible to recover encrypted information on the receiving side, is in this case 10^-6. Valid change OSNR, according to Figure 2, should not 10 to exceed 0.5 dB. This is equivalent to connecting to the line fiber optical coupler 11/89 or with a smaller branching ratio. When connecting the tap to listen to with a large coefficient of ommlette data loss occurs on the receiving side and the transmitting system stops the transmission of classified information.

Optical power branch (3) in the direction of the listening device (17) P₁₇will 89/11 ~ 8,1 times, or 9.1 dB less than the optical power in the line after the tap. Then we obtain: R₁₇<P₁₅+αL - 9,1, where P₁₅- power on the receiver (35), α is the loss coefficient of the fiber and standard loss fiber G.652: α = 0.2 dB/km, L is the length of the line from the listening position to the receiver (35). We assume that preternaturally receiving apparatus on the listening line is the same as in secret, i.e. capacity R₁₇= P₁₅. Then we obtain: L < 9,1/α ~ 45 km, it becomes impossible for unauthorized sampling data lines up to 45 km If necessary, design a secure line of greater length, it is broken down into several sections 45 km with the regeneration of the transmitted data.

Industrial applicability

The invention can be used in fiber-optical communication lines is highly sensitive to a length of 50 km for the transmission of coded information with a cryptographic algorithm that meets avalanche 5 criteria.

Literature

[1]. G.A.Barbosa, .Corndorf, P.Kumar and Nreap "Secure communicationusing mesoscopic coherent states", Physical Review Letters, Vol.90, No. 22, 227901 (2003).

[2]. E.Corndorf, C.Liang, G.S.Kanter, P.Kumar and H.P.Yuen "Quantum - noiserandomized data-encryption for WDM fiber-optic networks", Physical Review A. 2005.

[3]. Horst Feistel, "Cryptography and Computer Privacy." Scientific American, Vol.228, No. 5, 1973.

[4]. TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU G.975.1 (02/2004) Forward error correction for high bit-rate DWDM submarine systems.

1. How to send encrypted data over a bi-directional optical communication line error correction and attenuation of the transmitted in each direction of the optical signal and amplified on the receiving side, followed by narrow-band filtering,
characterized in that:
- the level of the received power of the optical signal communication line control and agree to give the her side, choosing his extremely low, commensurate with the level of optical quantum noise on the receiving side, and one with which it is still possible to recover lost bits of information while minimizing the optical loss in the optical line,
- the key to decrypt the packet bit data contained in the package and can vary from package to package,
- cryptographic algorithm that satises the avalanche criterion is chosen so that with the loss of at least one bit of the data packet decryption was impossible,
- optical communication line has high resistance to unauthorized listening due to the transmission of data at extremely high speeds in combination with extremely low-power signal transmitting side.

2. The method according to claim 1, in which encrypted data transmission is terminated by the fall of the level taken after amplification of the signal at a value ranging from 0.2 dB to 0.7 dB.

3. The method according to claim 1, in which encrypted data transmission stops if the maximum allowable level of corrected errors.

4. The method according to claim 1, in which encrypted data transmission is terminated by an unexpected change in time-of-flight line.

5. The method according to claim 1, in which the transmission is carried out by isotropic or anisotropic, or microstructure optical fiber into the well, or combinations thereof.

6. The method according to claim 1, in which the transmission rate is chosen as high as possible up to 100 Gbit/s and above in line with the length of up to 50 km

7. The method according to claim 6, in which coherent reception of an optical signal.

8. Optical communication encryption of data in two directions with error correction, containing for each direction cascaded optical:
transmitter with attenuator,
- receiving optical amplifier
photoelectronic Converter with an input narrow-band filter,
and characterized by the fact that increased resistance to unauthorized access to information communication is achieved by the fact that:
- the level of the received power of the optical signal communication line control and choose extremely low, commensurate with the level of quantum noise and such, which is still possible to recover lost bits of information
- the key to decrypt the packet bit data contained in the package and can vary from package to package,
- cryptographic algorithm that satises the avalanche criterion is chosen so that with the loss of at least one bit of the data packet decryption was impossible,
- optical communication line has high resistance to unauthorized the new listening due to the transmission of data at extremely high speeds in combination with extremely low-power signal transmitting side.

9. Optical communication line according to claim 8, in which encrypted data transmission is terminated by the fall of the signal level at the input of the optical receiver at a value ranging from 0.2 dB to 0.7 dB.

10. Optical communication line according to claim 8, in which encrypted data transmission stops if the maximum allowable level of corrected errors.

11. Optical communication line according to claim 8, in which encrypted data transmission is terminated by an unexpected change in time-of-flight line.

12. Optical communication line according to claim 8, in which the transmission is carried out by isotropic or anisotropic, or microstructure optical fiber, or combinations thereof.

13. Optical communication line according to claim 8, in which the transmission rate is chosen as high as possible up to 100 Gbit/s and above in line with the length of up to 50 km

14. Optical communication line according to item 13, in which the photoelectric Converter carries out the coherent conversion of the optical signal.