Paper 2006/009

Breaking and Fixing Public-Key Kerberos

Iliano Cervesato, Aaron D. Jaggard, Andre Scedrov, Joe-Kay Tsay, and Christopher Walstad


We report on a man-in-the-middle attack on PKINIT, the public key extension of the widely deployed Kerberos 5 authentication protocol. This flaw allows an attacker to impersonate Kerberos administrative principals (KDC) and end-servers to a client, hence breaching the authentication guarantees of Kerberos. It also gives the attacker the keys that the KDC would normally generate to encrypt the service requests of this client, hence defeating confidentiality as well. The discovery of this attack caused the IETF to change the specification of PKINIT and Microsoft to release a security update for some Windows operating systems. We discovered this attack as part of an ongoing formal analysis of the Kerberos protocol suite, and we have formally verified several fixes to PKINIT that prevent our attack.

Available format(s)
Cryptographic protocols
Publication info
Published elsewhere. Submitted to WITS'06; will be revised before publication if accepted.
PKINITman-in-the-middle attack
Contact author(s)
icervesato @ gmail com
2006-01-10: received
Short URL
Creative Commons Attribution


      author = {Iliano Cervesato and Aaron D.  Jaggard and Andre Scedrov and Joe-Kay Tsay and Christopher Walstad},
      title = {Breaking and Fixing Public-Key Kerberos},
      howpublished = {Cryptology ePrint Archive, Paper 2006/009},
      year = {2006},
      note = {\url{}},
      url = {}
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