TECH Signal 398
Decompiled 2004 RuneScape client reveals ISAAC-encrypted opcodes and 600ms ticks
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An article explains how the 2004 RuneScape client used a single TCP connection, ISAAC-encrypted opcodes, and 600ms server ticks to support multiplayer on 56k dial-up.
For engineers building low-bandwidth or real-time systems, the article demonstrates extreme byte-saving techniques: encrypting only the opcode, using a single TCP stream, and relying on a 600ms tick. These constraints forced a design that prioritizes minimal data over security and latency, offering lessons for constrained environments like IoT or mobile networks.
Written by elseif from the cluster below · every claim links back to a sourceThe three things worth knowing
The Java applet sandbox forced a single TCP connection, eliminating UDP and adding per-segment overhead.
Only the packet opcode is encrypted with the ISAAC stream cipher, leaving the body plaintext to save bytes.
Walk packets use a length byte and delta-encoded waypoints, and the server advances in 600ms cycles.
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