Secure Call: Principles of Private Communications
The foundational security philosophy of GNU Telephony, examining the telecommunications surveillance state, wiretapping vectors, the failure of centralized CAs, and the mathematical case for peer-to-peer ZRTP.
Historical Security Treatise
This document presents the political and technical security worldview of GNU Telephony circa 2007-2011. While the threat model remains strikingly relevant, consult modern cryptographic standards for new deployments.
§1The Modern Telecommunications Threat Model
For over a century, public telecommunications systems were built under state-mandated surveillance models. In the United States, CALEA (Communications Assistance for Law Enforcement Act) legally mandated that telephone switches incorporate backdoors for law enforcement access. Similar regulations were enacted worldwide.
When voice migrated to the Internet, commercial entities realized that metadata was as valuable as voice recordings. Centralized voice providers (Skype, Vonage, Google Voice, and cellular carriers) accumulate: - Complete social interaction graphs (who speaks to whom, when, and for how long). - Physical geolocation logs of both callers. - Unencrypted audio captures for transcription, advertising analysis, or intelligence sharing.
True privacy cannot exist on a network where a third-party server mediates the session keys.
§2The Three Pillars of Secure Calling
GNU Telephony formulated three non-negotiable architectural requirements:
1. End-to-End Cryptography: Encryption keys must exist only in volatile RAM on the participants' end devices. No intermediary-not even the server routing the call-can hold the keys. 2. Peer-to-Peer Media Paths: RTP streams must travel directly between endpoints over the shortest Internet path, eliminating choke points where media can be intercepted. 3. Cryptographic Verification by Humans: The Short Authentication String (SAS) empowers the human voice to verify the mathematics of Diffie-Hellman exchanges, defeating sophisticated Man-in-the-Middle attacks without requiring trust in corporate Certificate Authorities.
This page reconstructs material originally published at gnutelephony.org. It has been formatted and annotated for archival preservation.
Historical source: GNU Telephony. Reproduced or adapted under the GNU Free Documentation License (GFDL) 1.2 or later where stated.
Historical revision date: 2007-09-01 (Revised 2011-04-05). Restored to permanent static archive in October 2026.