---
_id: '60503'
abstract:
- lang: eng
  text: 'Censors have long censored Transport Layer Security (TLS) traffic by inspecting
    the domain name in the unencrypted Server Name Indication (SNI) extension. By
    encrypting the SNI extension, the Encrypted ClientHello (ECH) prevents censors
    from blocking TLS traffic to certain domains. Despite this promising outlook,
    ECH’s current capability to contest TLS censorship is unclear; for instance, Russia
    has started censoring ECH connections successfully. This paper clarifies ECH’s
    current role for TLS censorship. To this end, we evaluate servers’ support for
    ECH and its analysis and subsequent blocking by censors. We determine Cloudflare
    as the only major provider supporting ECH. Additionally, we affirm previously
    known ECH censorship in Russia and uncover indirect censorship of ECH through
    encrypted DNS censorship in China and Iran. Our findings suggest that ECH’s contribution
    to censorship circumvention is currently limited: we consider ECH’s dependence
    on encrypted DNS especially challenging for ECH’s capability to circumvent censorship.
    We stress the importance of censorship-resistant ECH to solve the long-known problem
    of SNI-based TLS censorship.'
author:
- first_name: Niklas
  full_name: Niere, Niklas
  id: '63563'
  last_name: Niere
- first_name: Felix
  full_name: Lange, Felix
  id: '67893'
  last_name: Lange
- first_name: Nico
  full_name: Heitmann, Nico
  id: '74619'
  last_name: Heitmann
  orcid: 0009-0003-7687-7044
- first_name: Juraj
  full_name: Somorovsky, Juraj
  id: '83504'
  last_name: Somorovsky
  orcid: 0000-0002-3593-7720
citation:
  ama: 'Niere N, Lange F, Heitmann N, Somorovsky J. Encrypted Client Hello (ECH) in
    Censorship Circumvention. In: ; 2025.'
  apa: Niere, N., Lange, F., Heitmann, N., &#38; Somorovsky, J. (2025). <i>Encrypted
    Client Hello (ECH) in Censorship Circumvention</i>. Free and Open Communications
    on the Internet, Washington, D.C.
  bibtex: '@inproceedings{Niere_Lange_Heitmann_Somorovsky_2025, title={Encrypted Client
    Hello (ECH) in Censorship Circumvention}, author={Niere, Niklas and Lange, Felix
    and Heitmann, Nico and Somorovsky, Juraj}, year={2025} }'
  chicago: Niere, Niklas, Felix Lange, Nico Heitmann, and Juraj Somorovsky. “Encrypted
    Client Hello (ECH) in Censorship Circumvention,” 2025.
  ieee: N. Niere, F. Lange, N. Heitmann, and J. Somorovsky, “Encrypted Client Hello
    (ECH) in Censorship Circumvention,” presented at the Free and Open Communications
    on the Internet, Washington, D.C., 2025.
  mla: Niere, Niklas, et al. <i>Encrypted Client Hello (ECH) in Censorship Circumvention</i>.
    2025.
  short: 'N. Niere, F. Lange, N. Heitmann, J. Somorovsky, in: 2025.'
conference:
  end_date: 2025-07-14
  location: Washington, D.C.
  name: Free and Open Communications on the Internet
  start_date: 2025-07-14
date_created: 2025-07-03T07:14:00Z
date_updated: 2026-08-17T07:40:46Z
ddc:
- '006'
file:
- access_level: local
  content_type: application/pdf
  creator: nniklas
  date_created: 2025-07-03T07:11:14Z
  date_updated: 2026-08-17T07:40:46Z
  file_id: '60505'
  file_name: foci-2025-0016.pdf
  file_size: 755171
  relation: main_file
file_date_updated: 2026-08-17T07:40:46Z
has_accepted_license: '1'
keyword:
- censorship
- circumvention
- ECH
- TLS
language:
- iso: eng
main_file_link:
- open_access: '1'
  url: https://www.petsymposium.org/foci/2025/foci-2025-0016.pdf
oa: '1'
status: public
title: Encrypted Client Hello (ECH) in Censorship Circumvention
type: conference
user_id: '63563'
year: '2025'
...