Background ECDH precomputation (#497)#489
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Add EcdhPrecomputeCache: a background thread precomputes ECDH shared secrets with all known participant public keys. When encryptFor is called, it checks the cache — if the ECDH is already computed, only KDF + AES remains on the critical path (~0.03ms instead of ~0.4ms per recipient). Each precomputed entry is consumed exactly once (forward secrecy) and automatically refilled in the background. The output format is unchanged — existing decrypt code works without modification. For the Global Synchronizer with 20 SVs, after the cache warms up (~50ms), every CC transfer's encryption drops from ~8ms to ~0.6ms per view. The ECDH work still happens, but off the transaction's critical path. Implementation: - EcdhPrecomputeCache.scala: background precompute + consume cache with auto-refill. Uses BouncyCastle's ECDHBasicAgreement directly. - JcePureCrypto.scala: encryptWithPrecomputedEcdh using IESEngine with precomputed shared secret. ecdhPrecomputeCache field with periodic refill thread. - SyncCryptoApiParticipantProvider.scala: encryptFor checks precompute cache before falling back to full ECIES. Registers recipient keys for background precomputation. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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This was referenced Apr 16, 2026
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Closes #497
Summary
Precompute ECDH shared secrets with known participants in a background thread. When a transaction needs to encrypt views, the expensive ECDH key agreement (~0.36ms per recipient, 77% of ECIES cost) is already done — only KDF + AES remains on the critical path (~0.03ms).
Impact
Encrypt-side latency (submitter, warm cache):
Total CPU unchanged — the ECDH work still happens, just in a background thread between transactions instead of on the critical path. Cache warmup takes ~50ms (one background refill cycle).
Each precomputed entry is consumed exactly once (forward secrecy) and automatically refilled in the background.
Relation to other PRs
Test plan
SimplestPingIntegrationTestpasses🤖 Generated with Claude Code