Limiting the impact of unreliable randomness in deployed security protocols

Akhmetzyanova, Liliya and Cremers, Cas and Garratt, Luke and Smyshlyaev, Stanislav and Sullivan, Nick
(2020) Limiting the impact of unreliable randomness in deployed security protocols.
In: 33rd IEEE Computer Security Foundations Symposium, June 22-25, 2020.
Conference: CSF IEEE Computer Security Foundations Symposium (was CSFW)

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Many cryptographic mechanisms depend upon the availability of securely generated random numbers. In practice,the sources of random numbers can be unreliable for many reasons, including bugs, compromise or subversion of standards. While there exist ways to significantly reduce the impact of unreliable randomness, these typically do not work well with practical constraints, such as long-term keys stored in hardware security modules. In practice, even modern protocols like TLS 1.3 lack such mechanisms and are therefore highly vulnerable to unreliable randomness.We propose a wrapper construction that reduces the impact of untrusted randomness, and which is is compatible with, and effective in, existing deployments of protocols such as TLS. We provide a security analysis of the construction and elaborate on design choices and practical interpretations. Our findings show that it is possible to effectively harden deployed protocols against unreliable randomness.


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