Cryptology ePrint Archive: Report 2016/475

Nonce-Disrespecting Adversaries: Practical Forgery Attacks on GCM in TLS

Hanno Böck and Aaron Zauner and Sean Devlin and Juraj Somorovsky and Philipp Jovanovic

Abstract: We investigate nonce reuse issues with the GCM block cipher mode as used in TLS and focus in particular on AES-GCM, the most widely deployed variant. With an Internet-wide scan we identified 184 HTTPS servers repeating nonces, which fully breaks the authenticity of the connections. Affected servers include large corporations, financial institutions, and a credit card company. We present a proof of concept of our attack allowing to violate the authenticity of affected HTTPS connections which in turn can be utilized to inject seemingly valid content into encrypted sessions. Furthermore we discovered over 70,000 HTTPS servers using random nonces, which puts them at risk of nonce reuse if a large amount of data is sent over the same connection.

Category / Keywords: cryptographic protocols / TLS, AES, GCM, AEAD, nonce

Date: received 17 May 2016

Contact author: hanno at hboeck de

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Version: 20160519:150547 (All versions of this report)

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