from the announcement:
Tor 0.2.3.25, the first stable release in the 0.2.3 branch, features
significantly reduced directory overhead (via microdescriptors),
enormous crypto performance improvements for fast relays on new
enough hardware, a new v3 TLS handshake protocol that can better
resist fingerprinting, support for protocol obfuscation plugins (aka
pluggable transports), better scalability for hidden services, IPv6
support for bridges, performance improvements like allowing clients
to skip the first round-trip on the circuit ("optimistic data") and
refilling token buckets more often, a new "stream isolation" design
to isolate different applications on different circuits, and many
stability, security, and privacy fixes.
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