Paper 2019/1083

What's in a Downgrade? A Taxonomy of Downgrade Attacks in the TLS Protocol and Application Protocols Using TLS

Eman Salem Alashwali and Kasper Rasmussen


A number of important real-world protocols including the Transport Layer Security (TLS) protocol have the ability to negotiate various security-related choices such as the protocol version and the cryptographic algorithms to be used in a particular session. Furthermore, some insecure application-layer protocols such as the Simple Mail Transfer Protocol (SMTP) negotiate the use of TLS itself on top of the application protocol to secure the communication channel. These protocols are often vulnerable to a class of attacks known as downgrade attacks which targets this negotiation mechanism. In this paper we create the first taxonomy of TLS downgrade attacks. Our taxonomy classifies possible attacks with respect to four different vectors: the protocol element that is targeted, the type of vulnerability that enables the attack, the attack method, and the level of damage that the attack causes. We base our taxonomy on a thorough analysis of fifteen notable published attacks. Our taxonomy highlights clear and concrete aspects that many downgrade attacks have in common, and allows for a common language, classification, and comparison of downgrade attacks. We demonstrate the application of our taxonomy by classifying the surveyed attacks.

Available format(s)
Publication info
Published elsewhere. SecureComm 2018 Workshop on Applications and Techniques in Cyber Security
TLSSSLDowngrade attacksTaxonomySurveyTransportApplicatoinProtocol
Contact author(s)
eman alashwali @ gmail com
2019-09-24: received
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Creative Commons Attribution


      author = {Eman Salem Alashwali and Kasper Rasmussen},
      title = {What's in a Downgrade? A Taxonomy of Downgrade Attacks in the TLS Protocol and Application Protocols Using TLS},
      howpublished = {Cryptology ePrint Archive, Paper 2019/1083},
      year = {2019},
      note = {\url{}},
      url = {}
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