Implementing TLS with Verified Cryptographic Security

Karthikeyan Bhargavan, Cédric Fournet, Markulf Kohlweiss, Alfredo Pironti, Pierre-Yves Strub

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract / Description of output

TLS is possibly the most used protocol for secure communications, with a 18-year history of flaws and fixes, ranging from its protocol logic to its cryptographic design, and from the Internet standard to its diverse implementations. We develop a verified reference implementation of TLS 1.2. Our code fully supports its wire formats, ciphersuites, sessions and connections, re-handshakes and resumptions, alerts and errors, and data fragmentation, as prescribed in the RFCs; it interoperates with mainstream web browsers and servers. At the same time, our code is carefully structured to enable its modular, automated verification, from its main API down to computational assumptions on its cryptographic algorithms. Our implementation is written in F# and specified in F7. We present security specifications for its main components, such as authenticated stream encryption for the record layer and key establishment for the handshake. We describe their verification using the F7 typechecker. To this end, we equip each cryptographic primitive and construction of TLS with a new typed interface that captures its security properties, and we gradually replace concrete implementations with ideal functionalities. We finally typecheck the protocol state machine, and obtain precise security theorems for TLS, as it is implemented and deployed. We also revisit classic attacks and report a few new ones.
Original languageEnglish
Title of host publication2013 IEEE Symposium on Security and Privacy, SP 2013, Berkeley, CA, USA, May 19-22, 2013
Number of pages15
ISBN (Electronic)978-0-7695-4977-4
Publication statusE-pub ahead of print - 25 Jun 2013
Event2013 IEEE Symposium on Security and Privacy - The Westin St. Francis, San Francisco, CA, United States
Duration: 19 May 201322 May 2013


Conference2013 IEEE Symposium on Security and Privacy
Abbreviated titleIEEE SP 2013
Country/TerritoryUnited States
CitySan Francisco, CA
Internet address


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