How data is split can swing encrypted traffic classifier scores by 40 points

Standard random data splits inflate accuracy to near-perfect levels, while session-disjoint splits reveal performance at chance.

Independent
Mayan Sharma · Kriti Saini · Devansh Behl
Research Digest··2 min read
Illustration: How data is split can swing encrypted traffic classifier scores by 40 points
The authors show that the evaluation protocol, specifically how packet flows are partitioned into training and test sets, can change reported macro-F1 from 0.992 to 0.567 on the same model and code.

Using two public corpora of encrypted traffic (including a month of backbone QUIC traffic), the authors re-evaluated a common flow-level classifier under five split protocols: random, temporal, client-disjoint, session-disjoint, and server-disjoint.

How it works

before and after
STANDARD SPLIT (RANDOM PER FLOW)Encrypted traffic: raw flowsEncrypted trafficraw flowsRandom split: per flow, shuffles Pcap IDsRandom splitper flow, shuffles PcapIDsmacro-F1 0.992: inflated by label leakagemacro-F1 0.992inflated by labelleakageSESSION-DISJOINT SPLITflowsbundled bycapturetest set not seen by modelvalidatessplit axis(0.000Encrypted traffic: raw flows, but grouped byEncryptedtrafficraw flows, butgrouped bySession-disjoint split: keeps all flows from one Pcap onSession-disjoint…keeps all flowsfrom one Pcap onSingle-ID probe: decision tree on capture ID aloneSingle-IDprobedecision tree oncapture ID alonemacro-F1 0.567: true score, gap of 0.426macro-F10.567true score, gapof 0.426Diagnostic validated on two corpora (backbone QUIC vs. TLS); generalizability to VPN/Tor not shown.
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