Analysis of the AOL search corpus shows an average search query length of 17.42 bytes with an entropy of 4.48 bits/byte, yielding 78.04 bits of deniable information per HTTP GET request. This entropy matches real user search behavior, making entropy-based traffic analysis unable to distinguish Facade traffic from genuine search sessions.

By deploying covert channels inside legitimate high-traffic web services (e.g., OpenSearch sites), Facade raises the censor's cost of blocking to unacceptable collateral damage: blocking Facade requires blocking the legitimate web service, which harms local businesses and normal users. Facade explicitly assumes censors are unwilling to block major platforms such as AWS or popular search services.

§3.2, §5.1 defense

Facade encodes 78.04 bits per HTTP GET request using search-query terms, compared to Infranet's 3 bits per URL — a ~26× improvement — while maintaining comparable statistical deniability. StegoTorus encodes 12,000 bits per URL but offers no statistical deniability against traffic-pattern analysis.

§5.2, Table 1 evaluation

Facade routes all encoded HTTP requests through a Selenium-controlled Chrome browser instance, so every message the censor observes is generated by a real browser implementation. This defeats 'parrot attack' fingerprinting, which exploits discrepancies between a protocol emulator's responses to error conditions and those of the genuine client or server.

§4, §5.1 defense

Facade faces an inverse tradeoff between upstream throughput and deniability: pure search encoding maximizes bits per request (78.04 bits) but does not reflect real user click behavior, while mixing in click-range mapping (lg(k) bits per URL, k=8 → 3 bits) reduces throughput but better models normal browsing. Neither pure strategy is optimal; the design requires tuning the search-to-click ratio.

§5.2 evaluation

obfs4 and obfs⋆ produce characteristic wire patterns—bursts of roughly MTU-sized payloads followed by a randomly-sized chaff packet—that CNN classifiers detect purely from packet-size sequences without payload inspection. A trivial per-bridge entropy-biasing re-encoding (obfs⋆) completely defeats the hand-tuned decision tree (0% precision, 0% recall) but does not reduce CNN detectability, because the CNN generalizes across size-distribution variants.

2024-wails-precisely §V-E, §IV-D-3, Figure 4 traffic-shapeml-classifierrandom-payload-detect

Meteor is proven secure against chosen-hiddentext attacks: any PPT adversary distinguishing Meteor output from honest model output can be reduced to breaking the underlying PRG. The scheme produces stegotext provably indistinguishable from the generative model's own output distribution, and requires only a shared public model — not a secret channel — making the model analogous to a common random string. On GPU the encoding overhead is ~1× model-load time; on CPU ~4.6×; on mobile ~49.5×.

2021-kaptchuk-meteor §5.2 / §6 / Table 2 random-payload-detectml-classifiertraffic-shape

The GFW's passive classifier uses two features of the first data packet to flag probable Shadowsocks traffic: (1) high Shannon entropy (per-byte entropy > ~7 bits strongly correlates with replay probability, which is nearly 4x higher at entropy 7.2 than at 3.0) and (2) packet length in the range 160–700 bytes with specific remainders mod 16. A single data packet after the TCP handshake is sufficient to trigger the downstream active-probing pipeline.

2020-alice-shadowsocks-detection §4.2 dpirandom-payload-detecttraffic-shape

Wiley's Bayesian classifier against obfuscated protocols (Dust, SSL, obfs-openssh) found that entropy detection achieved 94% accuracy using only the first packet, timing-based detection achieved 89% accuracy over entire packet streams, and length-based detection achieved only 16% accuracy.

2016-khattak-sok §2.4.1 random-payload-detecttraffic-shapeml-classifier

Obfsproxy3 and obfsproxy4 are reliably detected by an entropy-distribution test (KS test, block size k=8) applied to the first 2,048 bytes of the first client-to-server packet, combined with a minimum payload-length check of 149 bytes. On three university campus datasets totaling over 14 million TCP flows, the test achieves TPR=1.0 with FPR ranging from 0.24% to 0.33%. Omitting the length check raises the SSL/TLS false-positive rate to approximately 23%.

2015-wang-seeing §5.1, Table 5 dpirandom-payload-detecttraffic-shape

SSH transfers utilized only 15% of available bandwidth versus 85–89% for HTTP/HTTPS. When SSH was obfuscated by XORing payloads with a constant key (hiding the plaintext handshake), throughput dropped to near-zero during all trials. Applying the same obfuscation to HTTP transfers produced the same near-zero result, supporting the hypothesis that Iran whitelists known-approved protocols rather than blacklisting specific ones, which would preemptively block any unrecognized or randomized transport including Tor's obfsproxy.

2013-aryan-internet §4.4 traffic-shapethrottlingrandom-payload-detect