The present application is related to U.S. patent application Ser. No. 10/803,509, entitled “Systems and Methods for Implementing Routing Protocols for Quantum Cryptographic Key Transport,” and filed on Mar. 18, 2004; and U.S. patent application Ser. No. 09/611,783 entitled “Systems and Methods for Implementing a Quantum-Cryptographic Communications Network,” and filed on Jul. 7, 2000, the disclosures of which are incorporated by reference herein in their entirety.
The present invention relates generally to cryptographic systems and, more particularly, to systems and methods for implementing routing protocols and algorithms for key transport in quantum cryptographic systems.
Conventional packet-switching networks permit cheap and reliable communications independent of the distance between a source node and a destination node in the network. These conventional networks often rely upon either public keys or shared private keys to provide privacy for messages that pass through the network's links. Public key cryptographic systems have the drawback that they have never been proven to be difficult to decipher. Therefore, it is possible that a method of efficiently cracking public key systems may one day be discovered. Such a discovery could make all public key technology obsolete. All supposedly “secure” networks based on public key technology would thus become vulnerable. Shared private keys also have the drawback that the logistics of distributing the private keys can be prohibitive.
Quantum cryptography represents a recent technological development that provides for the assured privacy of a communications link. Quantum cryptography is founded upon the laws of quantum physics and permits the detection of eavesdropping across a link. Quantum cryptographic techniques have been conventionally applied to distribute keys from a single photon source to a single photon detector, either through fiber optic strands or through the air. Although this approach is perfectly feasible for scientific experiments, it does not provide the kind of “anyone to anyone” connectivity that is provided by current communications technology. Conventional quantum cryptographic techniques require a direct connection to anyone with whom one wishes to exchange keying material. Obviously, a large system built along these lines would be impractical, since it would require every person to have enough sources and/or detectors, and fiber strands so that they could employ a dedicated set of equipment for each party with whom they intend to communicate.
Furthermore, conventional quantum cryptographic techniques fail to adequately handle the situations in which eavesdropping is present on a link or when a dedicated link fails (e.g., a fiber is accidentally cut). In conventional quantum cryptographic techniques, further key distribution across the dedicated link becomes impossible until eavesdropping on the link ceases or the link is repaired. In addition, there may exist situations in which a single quantum cryptographic link may not be able to connect two endpoints, such as, for example, if the distance between the two endpoints causes too much signal attenuation, or because the two endpoints use different, incompatible optical encoding schemes.
It would, thus, be desirable to implement a quantum cryptographic network that could provide the “any to any” connectivity of conventional packet-switching networks, such as the Internet, while eliminating the need for a direct connection between parties transporting quantum cryptographic key material, and which may further sustain key distribution even with link failure and/or when eavesdropping exists on the link.
Therefore, there exists a need for systems and methods that combine the assured privacy achieved with quantum cryptography with the distance independent communication achieved with conventional multi-node, multi-link packet switching networks.
Systems and methods consistent with the present invention address this and other needs by implementing routing protocols and algorithms in a quantum cryptographic network, that includes multiple nodes, for transporting secret keys from one end of the quantum cryptographic key distribution (QKD) network to another. Link metrics associated with each link of the QKD network may be determined and then disseminated throughout the network. The link metrics may be determined, in some implementations, based on a number of secret key bits exchanged between each node connected by a respective link. The disseminated link metrics may be used to determine one or more paths through the QKD network for transporting end-to-end keys that can be used by QKD endpoints for encrypting/decrypting data sent across a public channel.
In accordance with the purpose of the invention as embodied and broadly described herein, a method of transporting keys in a quantum cryptographic key distribution (QKD) network includes determining one or more paths for transporting secret keys, using QKD techniques, across a QKD network. The method further includes transporting the secret keys across the QKD network using the determined one or more paths.
In a further implementation consistent with the present invention, a method of determining link metrics of quantum cryptographic links connecting a node to neighboring nodes in a quantum cryptographic key distribution (QKD) network is provided. The method includes exchanging secret key bits with each of the neighboring nodes using quantum cryptographic mechanisms via the quantum cryptographic links and determining a respective number of available secret key bits exchanged with each of the neighboring nodes. The method further includes determining link metrics associated with each of the quantum cryptographic links based on the respective number of secret key bits exchanged with each of the neighboring nodes.
In an additional implementation consistent with the present invention, a method of determining a link metric for each direction along quantum cryptographic links in a quantum cryptographic key distribution (QKD) network includes exchanging quantities of secret key bits between neighboring nodes in the QKD network using quantum cryptographic mechanisms over the quantum cryptographic links. The method further includes determining link metrics for each direction along each respective quantum cryptographic link of the quantum cryptographic links based on the exchanged quantities of secret key bits.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and, together with the description, explain the invention. In the drawings,
The following detailed description of the invention refers to the accompanying drawings. The same reference numbers in different drawings may identify the same or similar elements. Also, the following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims and their equivalents.
Systems and methods consistent with the present invention provide mechanisms for routing secret encryption/decryption keys across a QKD network. Routing, consistent with the present invention, may use link metrics derived, in some implementations, from a number of secret key bits exchanged between each node connected by a respective link. The derived link metrics may be used in a number of routing algorithms for determining at least one “best” path through the QKD network for subsequent end-to-end key transport.
QKD endpoints 105a and 105b may each include a host or a server. QKD endpoints 105a and 105b that include servers may further connect to private enclaves 120a and 120b, respectively. Each private enclave 120 may include local area networks (LANs) (not shown) interconnected with one or more hosts (not shown). Sub-network 110 can include one or more circuit-switched or packet-switched networks of any type, including a Public Land Mobile Network (PLMN), Public Switched Telephone Network (PSTN), LAN, metropolitan area network (MAN), wide area network (WAN), Internet, or Intranet. The one or more PLMNs may further include packet-switched sub-networks, such as, for example, General Packet Radio Service (GPRS), Cellular Digital Packet Data (CDPD), and Mobile IP sub-networks.
QKD sub-network 115 may include one or more QKD relays (QKD relays 205A and 205H shown for illustrative purposes only) for transporting end-to-end secret keys between a source QKD endpoint (e.g., QKD endpoint 105a) and a destination QKD endpoint (e.g., QKD endpoint 105b). The QKD relays of QKD sub-network 115 may include trusted relays. Trusted QKD relays may include QKD relays that consist of a known or assumed level of security.
Consistent with the present invention, each QKD relay 205 and QKD endpoint 105 of sub-network 115 may exchange secret key bits, via QKD techniques, with each of its neighboring QKD relays. For example, as shown in
Subsequent to key transport via QKD sub-network 115, QKD endpoint 105a and QKD endpoint 105b may encrypt end-to-end traffic using the transported key(s) and transmit the traffic via sub-network 110.
where q is associated with a number of shared secret bits for a given link. In some implementations, for example, q may represent a number of blocks of known size of shared secret bits. In other implementations, q may represent just the number of individual shared secret bits for the given link.
Each link of QKD sub-network 115 may have either “simplex” or “duplex” link metrics. A link with a “simplex” link metric may have a single metric for both directions along the link. A link with “duplex” link metrics may have two distinct metrics, one for each direction along the link. For example,
Processing unit 505 may perform all data processing functions for inputting, outputting, and processing of data. Memory 510 may include Random Access Memory (RAM) that provides temporary working storage of data and instructions for use by processing unit 505 in performing processing functions. Memory 510 may additionally include Read Only Memory (ROM) that provides permanent or semi-permanent storage of data and instructions for use by processing unit 505. Memory 510 can include large-capacity storage devices, such as a magnetic and/or optical recording medium and its corresponding drive.
Input device 515 permits entry of data into QKD relay 205 and includes a user interface (not shown). Output device 520 permits the output of data in video, audio, and/or hard copy format. Network interface(s) 525 interconnect QKD relay 205 with sub-network 110 via links unprotected by quantum cryptographic techniques. QCLI 530-1 through QCLI 530-N interconnect QKD relay 205 with QKD sub-network 115 via links protected by quantum cryptographic techniques. Bus 535 interconnects the various components of QKD relay 205 to permit the components to communicate with one another.
Photon source 540 may include, for example, a conventional semiconductor laser. Photon source 540 produces photon signals according to instructions provided by processing unit 505. Phase/polarization modulator 545 may include, for example, conventional semiconductor phase modulators or conventional liquid crystal polarization modulators. Phase/polarization modulator 545 may encode outgoing photon signals from photon source 540 according to commands received from processing unit 505 for transmission across an optical link.
Photon detector 550 can include, for example, conventional avalanche photo diodes (APDs) or conventional photo-multiplier tubes (PMTs). Photon detector 550 may detect photon signals received across an optical link from other QCLI's in QKD network 115.
Photon evaluator 555 can include conventional circuitry for processing and evaluating output signals from photon detector 550 in accordance with conventional quantum cryptographic techniques.
Each entry of QKD neighbor database 600 may include a neighbor node identifier 705, a number of shared bits value 710, a shared secret bit pool 715 and a link metric 720. Neighbor node identifier 705 may uniquely identify a neighboring node. In some implementations, for example, identifier 705 may include a network address of the neighboring node. In the example of
The exemplary process may begin with the exchange of secret key bits with neighboring nodes (i.e., QKD relays and QKD endpoints) of QKD network 115 via quantum key distribution [act 905]. For example, as shown in
A current link metric of each link with each respective neighboring node may be determined based on a number of shared secret bits 710 in a corresponding pool of shared secret bit pools 715 [act 915]. For example, a number of shared secret bits 710 for neighbor QKD relay 205A may be retrieved from QKD neighbor database 600 and a link metric may be assigned to the link between QKD relay 205B and QKD relay 205A based on the retrieved number of shared secret bits 710. Metrics associated with each link may determined in a number ways, including, for example, as a function of the number of currently available secret key bits exchanged between two relays at each end of a respective link. The one or more metrics associated with each link may be determined in other exemplary ways, including, for example, basing a link metric on rates of change in a number of secret bits shared between two relays, a time series average of a number of secret bits shared between two relays, and/or predictions of the number of shared secret bits that will be available at two relays interconnected by a respective link. In one implementation, a metric Mlink for each link may be determined in accordance with Eqn (1):
where q is associated with a number of shared secret bits for a given link. In some implementations, for example, q may represent a number of blocks of known size of shared secret bits. In other implementations, q may represent just the number of individual shared secret bits for the given link. The determined link metrics may then be stored [act 920]. The determined link metrics may be stored, for example, as link metric values 720 in QKD neighbor database 600.
The determined link metrics may further be disseminated [act 925] via, for example, a link state advertisement 800. Before disseminating link state advertisement 800, an originating node identifier 805 and an appropriate sequence number 810 may be inserted in advertisement 800. Additionally, each link metric associated with a link to a neighboring node may be inserted in the QKD link metrics 820 portion of link state advertisement 800. In some implementations consistent with the invention, the determined link metrics may be reliably “flooded” to neighboring QKD relays. In other implementations consistent with the invention, the determined link metrics may be disseminated to a centralized “route server,” which may subsequently be queried by any given node in QKD network 115 to determine a link metric associated with a particular link. In some implementations, for example, a link state advertisement 800 may be disseminated if an entire pool of shared secret bits suddenly runs low such that other nodes in QKD network 115 can be informed that the link metric has changed significantly for that particular link. A link state advertisement 800 may be disseminated periodically. In some implementations, a link state advertisement 800 may be disseminated asynchronously.
The exemplary process may begin with the receipt of link metrics from neighboring nodes in QKD network 115 [act 1005]. Link metrics may be received in link state advertisements 800 sent from other nodes in QKD network 115. Each received link metric may be stored, for example, in a link metric value 720 of QKD neighbor database 600 [act 1010]. A QKD network graph may then be constructed using the stored link metrics [act 1015]. Conventional graph algorithms may be used for constructing a graph of QKD network 115 using the stored link metrics. One or more paths may then be determined to every node in QKD network 115 for key transport using the constructed QKD network graph [act 1020]. The one or more paths may be determined using conventional path determination algorithms, such as, for example, the Shortest Path First (SPF) algorithm. Other conventional algorithms, though, may be equivalently used, such as, for example, conventional algorithms that determine two or more disjoint, or partially disjoint, paths through a network. Subsequent to the determination of one or more paths to every node in QKD network 115, secret keys may be transported over the determined one or more paths. In some implementations, for example, key transport may be implemented as described in the related and above-noted co-pending application Ser. No. 10/803,509, entitled “Systems and Methods for Implementing Routing Protocols for Quantum Cryptographic Key Transport.”
Systems and methods consistent with the present invention, therefore, provide mechanisms for routing end-to-end keys across a QKD network. Routing algorithms, consistent with the present invention, may employ link metrics associated with each link of the QKD network that can be determined based on a number of secret key bits exchanged between each node connected by a respective link. The determined link metrics may then be disseminated throughout the network so that conventional graph theory algorithms may be employed to determine one or more paths through the QKD network. The determined one or more paths may be used for transporting end-to-end keys that can be used by QKD endpoints for encrypting/decrypting data sent across a public channel.
The foregoing description of implementations of the present invention provides illustration and description, but is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. For example, instead of a single centralized “route” server, used in some implementations as described above, for storing link metrics and determining paths through QKD sub-network 115, multiple redundant “route” servers may be employed. Additionally, a hierarchical or “regional” set of “route” servers may be employed for large QKD networks. Furthermore, though some implementations of the present invention have been described as using link-state protocols, other non-link state routing protocols, such as, for example, distance vector, RIP, BGP, PNNI, or so called “on demand” protocols, such as AODV and DSR, may be employed.
While series of acts have been described in
The scope of the invention is defined by the following claims and their equivalents.
The instant application claims priority from provisional application No. 60/456,815, filed Mar. 21, 2003, the disclosure of which is incorporated by reference herein in its entirety.
The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of Contract No. F30602-01-C-0170, awarded by the Defense Advanced Research Projects Agency (DARPA).
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