Interferometric quantum cryptographic key distribution system

• US 5,307,410 A
• Filed: 05/25/1993
• Issued: 04/26/1994
• Est. Priority Date: 05/25/1993
• Status: Expired due to Term

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Bennett, Charles H.
• Primary Examiner(s): Barron, Jr., Gilberto
• Application Number:
  US08/066,743
• Time in Patent Office: 336 Days
• Field of Search: 380/21, 380/43, 380/44, 380/33, 380/54, 380/59, 359/112, 359/118
• US Class Current: 380/256
• CPC Class Codes: H04B 10/70 Photonic quantum communication
• CPC Class Codes: H04L 2209/08 Randomization, e.g. dummy operations or using noise
• CPC Class Codes: H04L 2209/80 Wireless network architectures or network communication protocols for wireless network security H04W12/00
• CPC Class Codes: H04L 9/0852 Quantum cryptography transmission systems employing electromagnetic waves other than radio waves, e.g. light, infrared H04B10/00; wavelength-division multiplex systems H04J14/02; WDM arrangements H04J14/03

Abstract

An apparatus and method for distributing cryptographic key information is described incorporating a quantum channel for conveying dim and reference light pulses, a timing channel, a source of coherent light pulses, beamsplitters, a random number generator, a phase modulator and a memory for recording the phase of transmitted dim light pulses. A cryptographic key receiver is described incorporating beam splitters, a random number generator, a phase modulator, a detector and a memory for recording the phase of received dim light pulses. The invention overcomes the problem of distributing fresh cryptographic key information between two users who share no secret information initially.

Claims

1. A secure communication network for sending messages unintelligible to an eavesdropper comprising:

a plurality of communication nodes, each having a first, second and third port,

a first quantum channel for conveying dim and reference light pulses connected to said first port of said plurality of communication nodes,

a second timing channel for conveying timing signals connected to said second port of said plurality of communication nodes,

a third message channel for conveying information selected from the group consisting of plain text and encrypted text connected to said third port of said plurality of communication nodes,

at least one of said communication nodes including

first means for sending a plurality of dim light pulses of coherent light of an intensity less than 1 expected photon per dim pulse spaced apart in time over said first quantum channel,

second means for sending a plurality of reference light pulses of coherent light positioned in time with respect to said plurality of dim light pulses over said first quantum channel,

a random number generator for generating random numbers,

a phase modulator coupled to said first means and to said random number generator for setting the phase of said plurality of dim light pulses, said phase of each said dim light pulse chosen randomly from a plurality of predetermined values in response to said random numbers,

third means for recording the phases of said plurality of dim light pulses sent over said first quantum channel,

fourth means for sending timing signals over said second timing channel, and

fifth means for sending and receiving information over said third message channel,

at least another one of said communication nodes including sixth means connected to said first quantum channel for receiving and detecting at least some of said dim light pulses and their respective phase relative to the phase of respective ones of said plurality of reference pulses as a function of time,

seventh means for recording the phases of said plurality of dim light pulses received over said quantum channel as a function of time, and

eighth means for sending and receiving information over said third message channel.

7. The apparatus of claim 1 wherein said another one of said n communication nodes includes:

a random number generator for generating random numbers,

a phase modulator connected to said first port and to said random number generator for setting the phase of said reference light pulse by a plurality of predetermined values in response to said random numbers,

fifth means for attenuating said bright pulse,

sixth means for time shifting said dim pulse with respect to said bright pulse,

seventh means for combining said attenuated and phase modulated bright pulse with said time shifted dim pulse whereby constructive interference occurs to provide at least an expected one photon output or whereby destructive interference occurs to provide substantially no expected photon output,

eighth means for detecting said photon output at times constructive interference occurs,

ninth means for receiving timing signals over said second timing channel, and

tenth means for sending and receiving information over said third message channel.

2. An apparatus for distributing cryptographic key information from a first communication node to a second communication node comprising:

a first quantum channel for conveying dim and reference light pulses connected to said first and second communication nodes,

a second timing channel for conveying timing signals connected to said first and second communication nodes, said first communication node including

first means for sending a plurality of dim light pulses of coherent light of an intensity less than 1 expected photon per dim light pulse spaced apart in time over said first quantum channel,

second means for sending a plurality of reference light pulses positioned in time with respect to said plurality of dim light pulses over said first quantum channel,

a random number generator for generating random numbers,

a phase modulator coupled to said first means and to said random number generator for setting the phase of said plurality of dim light pulses, said phase of each said dim light pulse chosen randomly from a plurality of predetermined values in response to said random numbers,

third means for recording the phase of said dim light pulses as a function of time, and

fourth means for generating and sending a plurality of timing signals over said second timing channel,

said second communication node including fifth means connected to said first quantum channel for detecting at least some of said dim light pulses and their respective phase relative to respective ones of said plurality of reference pulses as a function of time, and

sixth means for recording the phases of said plurality of dim light pulses as a function of time.

3. An apparatus for generating cryptographic key information comprising:

a light source for generating and sending a plurality of dim light pulses of coherent light of intensity of less than 1 expected photon per dim pulse spaced apart in time,

a random number generator for generating random numbers,

a phase modulator coupled to said light source and to said random number generator for setting the phase of each of said plurality of dim light pulses, said phase chosen randomly from a plurality of predetermined values in response to said random numbers, and

first means for recording the respective phases of said plurality of dim light pulses as a function of time.

4. The apparatus of claim 3 wherein said light source includes means for generating and sending a plurality of reference light pulses positioned in time with respect to said plurality of dim light pulses.

5. The apparatus of claim 3 further including a quantum channel coupled to said phase modulator for distributing said plurality of dim light pulses.

6. An apparatus for receiving a plurality of dim light pulses comprising:

a first unsymmetric beamsplitter having a reflection/transmission ratio R coupled to a source of said plurality of dim light pulses,

first means for conveying said reflected plurality of dim light pulses a predetermined distance and to the reflection side of a second unsymmetric beamsplitter having a reflection/transmission ration R, and a detector positioned in the path of said reflected plurality of dim pulses from said second unsymmetric beamsplitter,

said first unsymmetric beamsplitter having a transmission path therethrough, through a phase modulator and through said second unsymmetric beamsplitter in alignment with said reflected plurality of dim light pulses to said detector whereby destructive or constructive phase interference occurs,

a random number generator, said phase modulator coupled to said random number generator for setting the phase of said plurality of dim light pulses on said transmission path with said phase of each said dim light pulse chosen randomly from a plurality of predetermined values in response to said random numbers.

8. A method for sending messages unintelligible to an eavesdropper in a communication network having:

a plurality of communication nodes, each having a first, second and third port,

a first quantum channel for conveying dim and reference light pulses connected to said first port of said plurality of communication nodes,

a second timing channel for conveying timing signals connected to said second port of said plurality of communication nodes,

a third message channel for conveying information selected from the group consisting of plain text and encrypted text connected to said third port of said plurality of communication nodes,

at least one of said communication nodes performing the steps of;

sending a plurality of dim light pulses of coherent light of an intensity less than 1 expected photon per dim pulse spaced apart in time over said first quantum channel,

sending a plurality of reference light pulses of coherent light positioned in time with respect to said plurality of dim light pulses over said first quantum channel,

setting the phase of said plurality of dim light pulses, said phase of each said dim light pulse chosen randomly from a plurality of predetermined values in response to said random numbers,

recording the phases of said plurality of dim light pulses sent over said first quantum channel,

sending timing signals over said second timing channel, and

sending and receiving information over said third message channel,

at least another one of said communication nodes performing the steps of receiving and detecting at least some of said dim light pulses and their respective phase relative to the phase of respective ones of said plurality of reference pulses as a function of time,

recording the phases of said plurality of dim light pulses received over said quantum channel as a function of time, and

sending and receiving information over said third message channel.

9. A method for distributing cryptographic key information from a first communication node to a second communication node connected together by

a first quantum channel for conveying dim and reference light pulses connected to said first and second communication nodes,

a second timing channel for conveying timing signals connected to said first and second communication nodes, said first communication node performing the steps of

sending a plurality of dim light pulses of coherent light of an intensity less than 1 expected photon per dim light pulse spaced apart in time over said first quantum channel,

sending a plurality of reference light pulses positioned in time with respect to said plurality of dim light pulses over said first quantum channel,

setting the phase of said plurality of dim light pulses, said phase of each said dim light pulse chosen randomly from a plurality of predetermined values in response to said random numbers,

recording the phase of said dim light pulses as a function of time, and

generating and sending a plurality of timing signals over said second timing channel,

said second communication node performing the steps of detecting at least some of said dim light pulses and their respective phase relative to respective ones of said plurality of reference pulses as a function of time, and

recording the phases of said plurality of dim light pulses as a function of time.

10. A method for generating cryptographic key information comprising the steps of:

generating and sending a plurality of dim light pulses of coherent light of intensity of less than 1 expected photon per dim pulse spaced apart in time,

setting the phase of each of said plurality of dim light pulses, said phase chosen randomly from a plurality of predetermined values in response to said random numbers, and

recording the respective phases of said plurality of dim light pulses as a function of time.