FINDING · DEFENSE
The Helol tunnel encodes data in the permutation of TLS CHLO list-type parameters (cipher suites, extensions, elliptic curves, signature hashing algorithms), achieving a median throughput of roughly 8–12 bytes/packet from cipher-suite permutation alone, significantly outperforming SNICat across median and upper quartiles. The per-packet payload from full factorial encoding is ⌊log₂ N!⌋ bits for a list of N elements, yielding ~17–22 bytes/packet at median cipher-suite list lengths observed in local captures.
From 2026-soosahabi-helol-tunnel-covert — Helol Tunnel: Covert Channel Exploitation of TLS Extensibility & Privacy Features · §6.1 / Figure 4–5 · 2026 · arXiv preprint
Implications
- Circumvention protocols can leverage TLS CHLO parameter ordering as a high-bandwidth, low-detectability side-channel for key exchange or bridge distribution — cipher-suite order alone carries ~17 bytes/packet at typical list lengths, requiring no payload modification.
- Prioritize cipher-suite ordering over extension or elliptic-curve ordering for any TLS-embedded signaling: cipher suites have the highest median list length (19–22 elements) and contribute the most bits per CHLO packet.
Tags
Extracted by claude-sonnet-4-6 — review before relying.