Slitheen++'s relay station introduces minimal overt forwarding overhead: 95% of setups saw downstream per-packet delays between 1 ms and a maximum of 4 ms, with on average only 0.0029% of downstream packets affected (peak 0.006% in any single scenario). Upstream delays were similarly low except for a single outlier near 60 ms caused by thread contention during crawling-induced relay load spikes.

Slitheen++ achieves a median covert site loading time of 7 seconds in the naive setup, rising to 8 seconds with crawling and 13 seconds with a 1-second thinking-time (TT) delay. The Baseline-to-Covert factor ranges from 3.7–8.5 without TT and from 7.6–21.4 when crawling and 1-second TT are combined, reflecting the fundamental tradeoff between stealth overt behavior and covert throughput.

§5 (Figure 1, Figure 2) evaluation

Slitheen++ embeds covert upstream data by applying HTTP/2-like header field compression to overt HTTP requests, using the recovered space for covert data placement. This ensures that neither timing information nor observable changes to packet sizes or delays can reveal decoy routing use to an omni-scientist passive censor. GZIP compression was explicitly avoided to prevent the CRIME side-channel attack.

§4 defense

The original Slitheen appended covert upstream data directly to overt HTTP requests, significantly changing upstream traffic patterns and enabling censor identification even when traffic is encrypted. This upstream traffic analysis vulnerability—absent from Slitheen's original threat model—is the primary weakness Slitheen++ addresses.

§1, §4 detection

A censor can identify Slitheen relay connections by observing that all packets in a suspected overt flow arrive in strict order while flows from the same source naturally exhibit out-of-order delivery: the relay station's traffic-server component reorders TCP segments to enable TLS record decryption, creating a statistically anomalous per-connection ordering pattern. The reordering buffer also increases per-packet round-trip times, providing a secondary timing signal.

§4, §6 detection

A three-stage detection pipeline exploiting the "dual-role" behavioral fingerprint of single-IP circumvention relays achieved 23.2% recall (96/414 ground-truth relays) with a 0.18% false-positive rate against 97,651 benign TLS servers, for an overall accuracy of 99.5%. The ground-truth set covered OpenVPN, WireGuard, and SOCKS relays identified in a 17 TB single-day backbone trace (WIDE Project, April 9, 2025).

2026-almutairi-server §3.4, Table 1 traffic-shapedpiflow-correlation

The paper identifies a fundamental architectural vulnerability in single-IP circumvention designs: a relay must generate new observable flows (via DNS or TLS SNI) to reach end services after receiving client connections, creating a detectable server-and-client behavioral contrast. A relay accessing user-facing domains (news, social media) scores high on a Relay Suspicion Score (w=0.9) versus infrastructure domains (w=0.1). The paper argues this host-level signal is censorship-invariant and cannot be concealed by link obfuscation.

2026-almutairi-server §2.4, §4 traffic-shapedpisni-blocking

AnyTLS's default padding scheme operates across 8 levels (stop=8), with initial padding fixed at 30 bytes, small-data padding 100–400 bytes, and medium-to-large data padding chains of 400–500 bytes continuing through multiple 500–1000 byte segments. The 'c' (continue) marker allows multi-stage padding sequences within a single connection burst.

2026-anon-anytls-anytls-sing-box-2026 §2.3 traffic-shapedpi

AnyTLS implements a persistent idle-session pool with configurable parameters: idle_session_check_interval (default 30s), idle_session_timeout (default 30s), and min_idle_session (default 5). The client maintains at least 5 pre-established TLS sessions at all times to enable fast connection reuse without a new TLS handshake per request.

2026-anon-anytls-anytls-sing-box-2026 §2.4, §5.3 tls-fingerprinttraffic-shape

Compared to peer protocols, AnyTLS rates 'medium' performance (vs. VLESS 'high', Hysteria2 'very high', TUIC 'high'), uses TCP/TLS transport (vs. UDP/QUIC for Hysteria2 and TUIC), and relies on padding-based obfuscation vs. REALITY/WebSocket (VLESS) or HTTP/3 framing (Hysteria2). Client ecosystem support is currently limited primarily to sing-box, vs. broad cross-client support for VLESS, Trojan, and Hysteria2.

2026-anon-anytls-anytls-sing-box-2026 §1.5, Table 1.5 traffic-shapetls-fingerprint

AnyTLS is a TLS-based proxy protocol maintained by the sing-box team, designed in 2024 and first released in the sing-box dev-next branch. Its core mechanism wraps arbitrary proxy traffic in standard TLS and applies a configurable padding scheme (Padding Scheme) to enhance traffic concealment while maintaining compatibility with standard TLS infrastructure.

2026-anon-anytls-anytls-sing-box-2026 §1.1–1.3 tls-fingerprinttraffic-shapedpi