SNI Field Blocking and Internet Censorship

Introduction

Last year, the Ministry of Culture, Sports and Tourism, the Korea Communications Commission, and the National Police Agency jointly announced measures to prevent copyright infringement through overseas sites, and intensively cracked down illegal overseas sites from May to July and promoted a copyright protection campaign. In order to prevent the infringement of copyright through overseas sites, it is difficult to prevent sanctions. However, it took a lot of time to deliberate on access blocking, and when using a secure protocol (https), it was difficult to protect copyright because it was not easy to block. Therefore, a technical method was applied that could block even if using secure protocol. In October 2018, DNS servers blocked and SNI field blocking was applied in February 2019 (Lee).

Figure 1.

Network blocking history in Korea

When the SNI field blocking was implemented, there were reports that https was blocked in news and various social media, and that internet censorship in Korea began. However, this is a misleading expression. To be precise, not all websites using https were banned, but were taken to prevent access to illegal sites using methods related to https. Specifically, SNI (Server Name Indication) blocking technology is introduced to block access to blacklist websites.