[{"keyword":["decryption contexts","EFAIL","OpenPGP","S/MIME","AEAD"],"language":[{"iso":"eng"}],"_id":"25336","department":[{"_id":"632"}],"series_title":"CCS '20","user_id":"83504","abstract":[{"text":"OpenPGP and S/MIME are two major standards for securing email communication introduced in the early 1990s. Three recent classes of attacks exploit weak cipher modes (EFAIL Malleability Gadgets, or EFAIL-MG), the flexibility of the MIME email structure (EFAIL Direct Exfiltration, or EFAIL-DE), and the Reply action of the email client (REPLY attacks). Although all three break message confidentiality by using standardized email features, only EFAIL-MG has been mitigated in IETF standards with the introduction of AEAD algorithms. So far, no uniform and reliable countermeasures have been adopted by email clients to prevent EFAIL-DE and REPLY attacks. Instead, email clients implement a variety of different ad-hoc countermeasures which are only partially effective, cause interoperability problems, and fragment the secure email ecosystem.We present the first generic countermeasure against both REPLY and EFAIL-DE attacks by checking the decryption context including SMTP headers and MIME structure during decryption. The decryption context is encoded into a string DC and used as Associated Data (AD) in the AEAD encryption. Thus the proposed solution seamlessly extends the EFAIL-MG countermeasures. The decryption context changes whenever an attacker alters the email source code in a critical way, for example, if the attacker changes the MIME structure or adds a new Reply-To header. The proposed solution does not cause any interoperability problems and legacy emails can still be decrypted. We evaluate our approach by implementing the decryption contexts in Thunderbird/Enigmail and by verifying their correct functionality after the email has been transported over all major email providers, including Gmail and iCloud Mail.","lang":"eng"}],"status":"public","publication":"Proceedings of the 2020 ACM SIGSAC Conference on Computer and Communications Security","type":"conference","title":"Mitigation of Attacks on Email End-to-End Encryption","doi":"10.1145/3372297.3417878","date_updated":"2022-08-03T09:57:27Z","publisher":"Association for Computing Machinery","date_created":"2021-10-04T18:58:37Z","author":[{"last_name":"Schwenk","full_name":"Schwenk, Jörg","first_name":"Jörg"},{"first_name":"Marcus","full_name":"Brinkmann, Marcus","last_name":"Brinkmann"},{"first_name":"Damian","full_name":"Poddebniak, Damian","last_name":"Poddebniak"},{"first_name":"Jens","last_name":"Müller","full_name":"Müller, Jens"},{"first_name":"Juraj","last_name":"Somorovsky","orcid":"0000-0002-3593-7720","full_name":"Somorovsky, Juraj","id":"83504"},{"last_name":"Schinzel","full_name":"Schinzel, Sebastian","first_name":"Sebastian"}],"place":"New York, NY, USA","year":"2020","page":"1647–1664","citation":{"apa":"Schwenk, J., Brinkmann, M., Poddebniak, D., Müller, J., Somorovsky, J., &#38; Schinzel, S. (2020). Mitigation of Attacks on Email End-to-End Encryption. <i>Proceedings of the 2020 ACM SIGSAC Conference on Computer and Communications Security</i>, 1647–1664. <a href=\"https://doi.org/10.1145/3372297.3417878\">https://doi.org/10.1145/3372297.3417878</a>","bibtex":"@inproceedings{Schwenk_Brinkmann_Poddebniak_Müller_Somorovsky_Schinzel_2020, place={New York, NY, USA}, series={CCS ’20}, title={Mitigation of Attacks on Email End-to-End Encryption}, DOI={<a href=\"https://doi.org/10.1145/3372297.3417878\">10.1145/3372297.3417878</a>}, booktitle={Proceedings of the 2020 ACM SIGSAC Conference on Computer and Communications Security}, publisher={Association for Computing Machinery}, author={Schwenk, Jörg and Brinkmann, Marcus and Poddebniak, Damian and Müller, Jens and Somorovsky, Juraj and Schinzel, Sebastian}, year={2020}, pages={1647–1664}, collection={CCS ’20} }","mla":"Schwenk, Jörg, et al. “Mitigation of Attacks on Email End-to-End Encryption.” <i>Proceedings of the 2020 ACM SIGSAC Conference on Computer and Communications Security</i>, Association for Computing Machinery, 2020, pp. 1647–1664, doi:<a href=\"https://doi.org/10.1145/3372297.3417878\">10.1145/3372297.3417878</a>.","short":"J. Schwenk, M. Brinkmann, D. Poddebniak, J. Müller, J. Somorovsky, S. Schinzel, in: Proceedings of the 2020 ACM SIGSAC Conference on Computer and Communications Security, Association for Computing Machinery, New York, NY, USA, 2020, pp. 1647–1664.","ama":"Schwenk J, Brinkmann M, Poddebniak D, Müller J, Somorovsky J, Schinzel S. Mitigation of Attacks on Email End-to-End Encryption. In: <i>Proceedings of the 2020 ACM SIGSAC Conference on Computer and Communications Security</i>. CCS ’20. Association for Computing Machinery; 2020:1647–1664. doi:<a href=\"https://doi.org/10.1145/3372297.3417878\">10.1145/3372297.3417878</a>","ieee":"J. Schwenk, M. Brinkmann, D. Poddebniak, J. Müller, J. Somorovsky, and S. Schinzel, “Mitigation of Attacks on Email End-to-End Encryption,” in <i>Proceedings of the 2020 ACM SIGSAC Conference on Computer and Communications Security</i>, 2020, pp. 1647–1664, doi: <a href=\"https://doi.org/10.1145/3372297.3417878\">10.1145/3372297.3417878</a>.","chicago":"Schwenk, Jörg, Marcus Brinkmann, Damian Poddebniak, Jens Müller, Juraj Somorovsky, and Sebastian Schinzel. “Mitigation of Attacks on Email End-to-End Encryption.” In <i>Proceedings of the 2020 ACM SIGSAC Conference on Computer and Communications Security</i>, 1647–1664. CCS ’20. New York, NY, USA: Association for Computing Machinery, 2020. <a href=\"https://doi.org/10.1145/3372297.3417878\">https://doi.org/10.1145/3372297.3417878</a>."},"publication_identifier":{"isbn":["9781450370899"]},"publication_status":"published"}]