- freely available
Future Internet 2017, 9(3), 26; doi:10.3390/fi9030026
- Identity Based Cryptography (IBC)—Shamir first introduced IBC in 1985 . In this cryptographic approach, user identifier information such as email address, IP address, and so forth are used as a public key for encryption and verification of digital signatures instead of certificates. In addition, in IBC, the Private Key Generator (PKG) is the central authority (similar to a Certificate Authority, CA in PKIs) which generates the private keys for participants.
- Public Key Infrastructure (PKI)—Traditional asymmetric or public key cryptography widely and effectively used in the Internet and a plethora of business realms relies on a PKI. The latter depends on the availability and security of a CA, a central control point that everyone trusts.
2.2. DTN Characteristics and Key Management
- Deep space networks —They are characterized by extremely long delays that typically cause memory and/or storage exhaustion.
- Sensor-based networks —Their idiosyncrasies include extremely low end-node power, memory, and CPU capability.
- Terrestrial wireless networks —This ilk of networks is characterized by high mobility and changes in signal strength.
- Vehicular AdHoc networks —They exhibit mobility, self-organization, distributed communication, and road-pattern restrictions.
- Satellite networks —They are characterized by long delays and high rate of packet loss.
- Rural area DTN —They are distinguished by opportunistic behaviour, sporadic and isolated message transmission.
2.3. Security in Real DTN Implementations
- ION —JPL’s implementation of the BP. It implements the BSP Bundle Authentication Block (BAB), Bundle Confidentiality Block (PCB) and Bundle Integrity Block (PIB) security blocks in versions greater than 3.0.0.
- IBR-DTN —BP implementation for embedded systems, which relies on the BSP specification.
- ByteWalla —BP implementation for Android devices. It implements the BSP PCB security block with AES in Galois Counter Mode (GCM).
3. Key Management Taxonomy in DTNs
3.1. Security Initialization
3.2. Key Establishment
3.2.1. Two-Party Communication
3.2.2. Group Communication
- Forward secrecy (FS)—requires that users who left the group and know a contiguous subset of old group keys cannot discover subsequent group keys. This ensures that a member cannot decrypt data sent immediately after it leaves the group.
- Backward secrecy (BS)—mandates that a new user that joins the group and knows a contiguous subset of group keys cannot discover preceding group keys. This ensures that a member cannot decrypt data sent before it joins the group.
- Collusion freedom (CF)—requires that any set of fraudulent users who have much information about past keys should be incapable of deducing the current used group key.
- Key independence (KI)—requires that a passive adversary who knows any proper subset of group keys cannot compromise other past or future group keys. That is, the combination of backward and forward secrecy yields key independence.
3.3. Key Revocation
3.4. Standardisation Efforts
5. Alternative Key Management Taxonomies in DTNs
5.1. Require or Not Trusted Third Party (TTP)
- Require TTP—Works such as [45,46,47,48,49] are based on PKI solutions mandate a TTP, and thus a CA. Works such as [12,24,25,26,40,41] that are founded on IBC solutions, require a TTP too, namely the PKG. In addition, schemes in group key management that rely on LKH such as [52,54], necessitate a TTP known as Key Distribution Center (KDC). Moreover, the work in , which is based on CPK, eliminates the need for online TTP and only needs an off-line PKG.
5.2. Centralised, Decentralised and Distributed
6. Open Research Challenges
- Key Management—As already mentioned, cryptographic key management is the major open issue in DTNs and especially in deep space communications. Section 3 presents and categorises all the schemes proposed until now. Constraints in resources such as memory, power, storage, computation, and bandwidth in DTN nodes put additional challenges on the key management. Resource-conscious key management techniques become a necessity in DTNs. The key management issues that require further research are listed below:
- Security initialisation—Security initialisation is an expensive procedure and considering the dynamic nature of DTNs is difficult to handle. As already discussed, the two main approaches are with either a TTP or self-organised. Both approaches have their advantages and disadvantages.
- Key update/key lifetime—Key lifetime is difficult to choose and must vary based on the different constraints of DTN environments. For instance, if the key update period is too long, the corresponding key may be exposed. If it is is too short, frequent updates can add large overhead.
- Key storage—Considering storage limitations in DTNs in general, and sensor or deep space DTNs in particular, each node must handle the number of possible keying material stored, based on a number of factors, including the number of neighbors, key validity, key expiration, key usage rate, length as well as other stored bundles. Apart from the volume, private keys must be stored securely to avoid compromisation.
- Key revocation—Key revocation is impractical in DTNs due to the nature of DTNs. Different approaches must be used instead, depending on the specific network constraints.
- Handling Replays—In DTN networks, due to scarce network resources, the replayed volume of messages must be reduced to the minimum possible. However, this is not always the case due to various DTN scenarios (i.e., authentication scenarios) where at least some replay messages are desirable. Moreover, the huge delays in such networks, complicates handling replays, and therefore the formulation of a DTN replay protection scheme becomes very challenging.
- Traffic Analysis—There are not any security services for protecting/deterring against traffic analysis. However, for some disruption tolerant networks such as military ones, hiding traffic is rather a sine qua non.
- Routing Protocol Security—There are no well-documented DTN routing protocols, so DTN routing protocol security is an open issue. However, some of the existing security features of the underlying protocols can be used.
- Multicast Security—Currently, there is no mechanism to separate between a multicast and anycast endpoint. DTN security architecture does not address the security aspects of enabling a DTN node to register with a particular multicast or anycast endpoint identifier at all.
- Performance Issues—Security within a DTN imposes both bandwidth utilization costs on the communication links and computational costs at the nodes. In addition, there may be certain limitations regarding how much CPU, storage, energy, and so on can be devoted to security, and the amount of computation costs will undoubtedly depend on the underlying algorithms and their associated parameters.
- Naming—DTN naming is a hard open issue to cope with . For instance, how names are to be used in routing, and the ways this will be mapped to the underlying routing of each convergence layer network, remains unclear. A properly constructed naming system can aid in simplifying both routing and security. That is, for security and resource allocation reasons, one would overwhelmingly prefer to be able to uniquely identify a source as well as to determine which group or groups this source may belong to.
7. Conclusions & Future Research
Conflicts of Interest
|DTNs||Delay Toleran Networks|
|PKI||Public Key Infrastructure|
|IBC||Identity Based Cryptography|
|PKG||Private Key Generator|
|BSP||Bundle Security Protocol|
|BAB||Bundle Authentication Block|
|PIB||Payload Integrity Block|
|PCB||Payload Confidentiality Block|
|GCM||Galois Counter Mode|
|HIBC||Hierarchical Identity Based Cryptography|
|DKE||Distributed Key Establishment|
|CRL||Certificate Revocation List|
|SKC||Secret Key Crypography|
|WoT||Web of Trust|
|DVD||Dynamic Virtual Digraph|
|BSP||Bundle Security Protocol|
|LCF||Leverage of Common Friends|
|CPK||Combined Public Key|
|ECC||Elliptic Curves Cryptography|
|PGP||Pretty Good Privacy|
|ESKTS||Efficient and Scalable Key Transport Scheme|
|DSC-KM||Digital Signature Chains Key Management Scheme|
|LKH||Logical Key Hierarchy|
|CRT||Chinese Remainder Theorem|
|AGKM||Autonomic Group Key Management|
|ONE||Opportunistic Networking Environment|
|ESB||Extension Security Block|
|ASB||Abstract Security Block|
|CCSDS||Consultative Committee for Space Data Systems|
|SBSP||Streamlined Bundle Security Protocol|
|BPSec||Bundle Protocol Security Specification|
|TTP||Trusted Third Party|
|KDC||Key Distribution Center|
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|Scheme||Crypto-Graphy||Methods/Protocols/Schemes||DTN Network||Evaluation Method||Architecture||Year|
|Seth, A., and Keshav, S. ||PKC/SKC||HIBC, Gentry-Silverberg HIBC (HIBE and HIBS),authorized distribution||Rural Area DTN||N/A||Centralised||2005|
|Asokan, N., Kostiainen, K., Ginzboorg, P., Ott, J.and Luo, C. ||PKC/SKC||IBC, cellular authentication infrastructure||Rural Area DTN||Theoretical||Centralised||2007|
|Patra, R., Surana, S., and Nedevschi, S. ||PKC||HIBC||Network-agnostic||N/A||Centralised||2008|
|El Defrawy, K., Solis, J., and Tsudik, G. ||PKC||social contact information||Rural Area DTN||Simulation||Decentralised/Distributed||2009|
|Du, J. and Kranakis, E., and Nayak, A. ||PKC/SKC||key pre-distribution, neighbor distributed key establishment (DKE)||Sensor and Actor Network DTN(DTLBS-WSAN)||Theoretical, Simulation||Decentralised/Distributed||2011|
|Shikfa, A., Önen, M., and Molva, R. ||PKC||self-organised, pseudonym certificates, encapsulated signatures||Opportunistic Networks||Theoretical||Decentralised/Distributed||2012|
|Jia, Z., Lin, X., Tan, S., Li, L., and Yang, Y. ||PKC||two-channel cryptography, dynamic virtual digraph (DVD)||pocket DTN||Simulation||Decentralised/Distributed||2012|
|Xie, Y., and Wang, G. ||SKC||distributed secret key generation system, self-certified identity||Network-agnostic||Simulation||Decentralised/Distributed||2013|
|Djamaludin, C.I., Foo, E., and Corke, P. ||PKC||PGP, Leverage of Common Friends (LCF) method||Network-agnostic||Simulation||Decentralised/Distributed||2013|
|Lv, X. and Mu, Y. and Li, H. ||PKC||two-channel cryptography, time evolving model||Space DTN||Simulation||Decentralised/Distributed||2014|
|Jadhav, C., Dhainje, P., and Pradeep, D. ||PKC||two-channel cryptography, time evolving model||Space DTN||N/A||Decentralised/Distributed||2015|
|Mukundhan E. and Veeramani, M.E. ||PKC||two-channel cryptography, time evolving mode||Space DTN||N/A||Decentralised/Distributed||2015|
|Scheme||Crypto-Graphy||Key Manage-Ment Area||Methods/Protocols/Schemes||DTN Network||Evaluation Method||Architecture||Year|
|Kate, A., Zaverucha, G., and Hengartner, U. ||PKC/SKC||key agreement||IBC, Sakai-Ohgishi-Kasahara (SOK) key agreementscheme and HIBC (HIBE and HIBS)||Rural Area DTN||Simulation||Centralised||2007|
|Van Besien, W.L. ||PKC/SKC||key pre-distribution, key distribution||IBC bilinear maps over elliptic curves||Network-agnostic||N/A||Centralised||2010|
|Ahmad, N., Cruickshank, H., and Sun, Z. ||PKC/SKC||key agreement||IBC||Rural Area DTN||N/A||Centralised||2010|
|Ding, Y., Zhou, X., Cheng, Z., and Zeng, W. ||PKC/SKC||key agreement||CPK (Combined Public Key), AKP protocol, ECC||Network-agnostic||Theoretical||Centralised||2013|
|Scheme||Crypto-Graphy||Key Manage-Ment Area||Methods/ Protocols/Schemes||DTN Network||Evaluation Method||Architecture||Year|
|Bhutta, M., Ansa, G. and Johnson, E., Ahmad, N.,Alsiyabi, M. and Cruickshank, H. ||PKC/SKC||key predistribution, manual keys,key establishment||PKI, proxy certificates||Satellite and Sensor DTN||N/A||Centralised||2009|
|Menesidou, S.A., and Katos, V. ||PKC/SKC||key agreement||PKI, HMP protocol||Space DTN||N/A||Centralised||2012|
|Johnson, E., Cruickshank, H., and Sun, Z. ||PKC||key pre-distribution||PKI||Satellite DTN||Simulation||Centralised||2013|
|Bhutta, M., Cruickshank HS., and Sun Z. ||PKC/SKC||key distribution||PKI, proxy signatures, Symmetric Key Transport,Efficient, Scalable Key Transport Scheme (ESKTS)||Network-agnostic||Simulation||Centralised||2014|
|Rajan, G., and Cho, G. ||PKC/SKC||key distribution||PKI||Network-agnostic||N/A||Centralised||2015|
|Andrade, D., and Albini, C. ||PKC||key establishment||PGP, DSC-KM||Network-agnostic||Simulation||Decentralised/Distributed||2016|
|Scheme||Crypto- Graphy||Security Properties||Methods/Protocols/Schemes||DTN Network||Evaluation Method||User Join Message Cost||User Leave Message Cost||Architecture||Year|
|Edelman, P., Donahoo, M., and Sturgill, D. ||PKC||FS, BS, KI, CF||Group Membership Tree (GMT), Logical Key Hierarchy (LKH), key graphs||Network-agnostic||Simulation||O (log n)||O (log n)||Centralised||2010|
|Xu, Gl, Chen, X., and Du, X. ||SKC||FS (one-to-manyscenario),BS, CF||XOR, Chinese Remainder Theorem, Chinese Remainder DTN Group Key(CRDGK) scheme, time-based group key management scheme||Network-agnostic||Simulation||O (1)||O (1)||Centralised||2012|
|Zhou, J., Song, M.m Song. J., Zhou, X.,and Sun, L. ||PKC||FS, BS, KI, CF||autonomic group key management (AGKM) scheme, Logical KeyHierarchy (LKH), one-encryption-key multi-decryption-key key protocol||Space DTN||Theoretical Proof, Simulation||O (log n)||O (1)||Centralised||2014|
|Gupta ||PKC||FS, BS, CF||Modified version of Chinese Remainder Theorem||Network-agnostic||Theoretical Proof, Simulation||O (1)||O (1)||Centralised||2016|
|Scheme||Crypto-Graphy||Methods/Protocols/Schemes||DTN Network||Evaluation Method||Architecture||Year|
|Djamaludin, C.I., Foo, E.,Camtepe, S. and Corke, P. ||PKC||DS revocation scheme, PGP,△CRL||Large scale DTNs(e.g., MANET, VANET)||Simulation||Decentralised/Distributed||2016|
|Bhutta, M. and Sun, Z. ||PKC||PKI, Hash Table, CRL||Network-agnostic||Simulation||Centralised||2017|
|Title||Naming Conventions||Released Date||Expiration Date|
|DTN Key Management Requirements ||draft-farrell-dtnrg-km-00||June 2007||December 2007|
|Delay-Tolerant Networking Security Overview ||draft-irtf-dtnrg-sec-overview-06||March 2009||September 2009|
|Bundle Security Protocol Specification ||RFC6257||May 2011||-|
|Space Mission Key Management Concept ||CCSDS 350.6-G-1||November 2011||-|
|Delay Tolerant Networking Security Key Management - Problem Statement ||draft-templin-dtnskmps-00||March 2014||September 2014|
|Streamlined Bundle Security Protocol Specification ||draft-irtf-dtnrg-sbsp-01||May 2014||November 2014|
|DTN Security Key Management - Requirements and Design ||draft-templin-dtnskmreq-00||February 2015||August 2015|
|Architecture for a Delay-and-Disruption Tolerant Public-Key Distribution Network (PKDN) ||draft-viswanathan-dtnwg-pkdn-00||August 2015||February 2016|
|Bundle Protocol Security Specification ||draft-ietf-dtn-bpsec-04||March 2017||September 2017|
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