DEFENSES
trojan Trojan (TLS-mimicking)
2 papers on file
- 2026-anon-gpt-6-astra GPT-6 Astra 跨过网络安全门槛：机场数据泄露、平台问责与吉隆恢复周报 | 二毛
- 2022-blocking-tls-circumvention Large scale blocking of TLS-based censorship circumvention tools in China
10 findings tagged here
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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.
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The article documents that large-scale 'one-click' commercial VPN providers with static protocol stacks have become effectively non-viable in China, while subscription-based proxy node services using open-source clients (Clash, Shadowrocket) with server-side rapid IP and datacenter switching demonstrate substantially greater resilience to GFW blocking waves.
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Per-flow RTTdiff detection rates are only ~20% because the majority of proxy flows connect to CDN-cached content (Cloudflare, Google, Fastly) that sits within 5ms of the proxy, suppressing the discrepancy. However, aggregating across flows per website visit yields detection rates exceeding 70%—and from the abstract, approximately 80% of top-5K domains generate at least one detectable flow—with half of those detections made within the first 60 packets. This means an adversary can reliably expose client and proxy IPs after just a few website visits.
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Cross-layer RTT discrepancy (RTTdiff) is a protocol-agnostic fingerprint that exploits an inherent architectural property of all proxy setups: transport-layer sessions terminate at the proxy while application-layer sessions remain end-to-end. Evaluation across 10 proxy protocols—including VMess, Shadowsocks, VLESS, Trojan, XTLS-Vision, and obfs4-wrapped SOCKS—shows near-identical detection rates for all except obfs4, confirming the fingerprint is not tied to any specific obfuscation scheme. At FPR=0.01, per-website detection rates exceed 70% across all tested client and proxy location combinations.
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LZR, built on top of ZMap, can identify 99% of unexpected Internet services in five handshakes by acting as a shim between ZMap and ZGrab. This gives censors and researchers alike an efficient active-probing primitive to fingerprint proxy protocols at scale.
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Obfuscated proxy traffic (including Shadowsocks, VMess, VLESS, Trojan, obfs4, and REALITY) can be reliably fingerprinted by detecting encapsulated TLS handshakes — the inner TLS ClientHello that appears inside an outer encrypted tunnel. This fingerprint is protocol-agnostic: any proxy that wraps TLS-bearing application traffic will produce it. The authors deployed a similarity-based classifier within a mid-size ISP serving over one million users and demonstrated detection with minimal collateral damage.
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Starting October 3, 2022, more than 100 users reported simultaneous blocking of TLS-based circumvention servers running Trojan, Xray, V2Ray TLS+WebSocket, VLESS, and gRPC. Blocking was port-specific initially (mainly port 443, but also non-443 ports), then escalated to full IP blocking when users switched ports. Domain names were not added to DNS or SNI blocklists. naiveproxy was notably not affected. The blocking was dynamic in at least some cases (browsers could still reach the port, but circumvention tools could not), strongly indicating protocol-level identification rather than blind port blocking.
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The October 2022 blocking wave is the confirmed operational deployment of the fully-encrypted-traffic detector later formalized in Wu et al. (USENIX Security 2023). The detector was therefore in live production from at least late 2022, more than a year before the academic paper describing it was published. This event establishes that the GFW's passive fully-encrypted classifier operates at scale in adversarial real-world conditions, not just in controlled experiments.
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Internet filtering in Saudi Arabia is implemented primarily as HTTP URL-keyword filtering augmented by TLS-level (SNI) filtering for HTTPS connections; DNS and IP-level failures were minimal and consistent with transient network issues rather than deliberate blocking. In 2019, 82.2% of Adult, 7.6% of Shopping, and 6.2% of Games websites returned HTTP 403; TLS filtering of Shopping sites decreased from 9.6% to 6.6% between 2018 and 2020.
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The protocol filter's HTTPS fingerprint requires only that the first 5 bytes match a TLS header (type 0x16, version 0x03 0x01–0x03, correct length field); all subsequent bytes of the Client Hello are unchecked. Any TLS-based circumvention tool naturally satisfies this fingerprint and will bypass the filter by default. Furthermore, any one of the three permitted fingerprints (DNS, HTTP, HTTPS) can be used on any of the three monitored ports to whitelist an entire flow.