The paper's threat model explicitly assumes censors can enforce client-side VoIP software (e.g., TOM-Skype in China) giving the adversary access to the pre-encoding audio signal at both endpoints. Despite this, SkypeLine forces the censor into an all-or-nothing position: intercepting hidden data requires blocking the entire VoIP service, since no network-layer observable (packet headers, timing, encrypted payload) distinguishes steganographic from legitimate calls.
From 2016-kohls-skypeline — SkypeLine: Robust Hidden Data Transmission for VoIP
· §3.1, §6.1
· 2016
· ASIA Computer and Communications Security
Implications
Choose cover channels the censor is economically or politically incentivized to keep available (commercial VoIP, CDN traffic, messaging platforms) — steganographic systems that force an all-or-nothing blocking choice inherit the political cost of collateral damage as a structural defense.
Assume endpoint compromise is possible in high-threat deployments (China, Iran); design steganographic schemes so that even with audio access, the adversary gains nothing without the pre-shared DSSS secret — DSSS session-key isolation is the critical security primitive here.