Paper 2018/089

The Unified Butterfly Effect: Efficient Security Credential Management System for Vehicular Communications

Marcos A. Simplicio Jr., Eduardo Lopes Cominetti, Harsh Kupwade Patil, Jefferson E. Ricardini, and Marcos Vinicius M. Silva


Security and privacy are important requirements for the broad deployment of intelligent transportation systems (ITS). This motivated the development of many proposals aimed at creating a Vehicular Public Key Infrastructure (VPKI) for addressing such needs. Among them, schemes based on pseudonym certificates are considered particularly prominent: they provide data authentication in a privacy-preserving manner while allowing vehicles to be revoked in case of misbehavior. Indeed, this is the approach followed by the Security Credential Management System (SCMS), one of the leading candidate designs for protecting vehicular communications in the United States. Despite SCMS's appealing design, in this article we show that it still can be further improved. Namely, one of the main benefits of SCMS is its so-called butterfly key expansion process, which allows batches of pseudonym certificates to be issued for authorized vehicles by means of a single request. Whereas this procedure requires the vehicle to provide two separate public/private key pairs for registration authorities, we present a modified protocol that uses a single key for the same purpose. As a result, the processing and bandwidth costs of the certificate provisioning protocol drop as far as 50%. Such performance gains come with no negative impact in terms of security, flexibility or scalability when compared to the original SCMS.

Note: Acknowledgements added and acceptance status updated

Available format(s)
Cryptographic protocols
Publication info
Published elsewhere. Minor revision. 2018 IEEE Vehicular Networking Conference (VNC)
Vehicular communicationssecurity and privacypseudonym certificatesbutterfly key expansion
Contact author(s)
mjunior @ larc usp br
2018-11-15: last of 4 revisions
2018-01-28: received
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Creative Commons Attribution


      author = {Marcos A.  Simplicio Jr. and Eduardo Lopes Cominetti and Harsh Kupwade Patil and Jefferson E.  Ricardini and Marcos Vinicius M.  Silva},
      title = {The Unified Butterfly Effect: Efficient Security Credential Management System for Vehicular Communications},
      howpublished = {Cryptology ePrint Archive, Paper 2018/089},
      year = {2018},
      note = {\url{}},
      url = {}
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