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fix BCH-01-004: rate-limit subscription-triggered announces

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Adds rate-limiting to prevent device enumeration attacks via rapid
subscription/disconnect cycles. Without this fix, an attacker could
enumerate ~120 bitchat devices per minute by connecting, subscribing,
capturing the announce packet, then disconnecting and moving to the next.

Key changes:
- Add per-central rate-limit tracking with exponential backoff
- Minimum 2-second interval between announces per central
- Exponential backoff (2x) up to 30 seconds for rapid reconnects
- After 5 rapid attempts, suppress announces entirely (likely attack)
- Clean up stale rate-limit entries after 60-second window
- Clear rate-limit state during panic mode

Configuration:
- bleSubscriptionRateLimitMinSeconds: 2.0
- bleSubscriptionRateLimitBackoffFactor: 2.0
- bleSubscriptionRateLimitMaxBackoffSeconds: 30.0
- bleSubscriptionRateLimitWindowSeconds: 60.0
- bleSubscriptionRateLimitMaxAttempts: 5

Security audit reference: Cure53 BCH-01-004 (Medium severity)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
This commit is contained in:
jack
2026-01-12 10:43:36 -10:00
co-authored by Claude Opus 4.5
parent b84c36c6fa
commit 99896bcded
3 changed files with 179 additions and 2 deletions
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bitchat/Services/TransportConfig.swift
+8
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@@ -162,6 +162,14 @@ enum TransportConfig {
static let blePostAnnounceDelaySeconds: TimeInterval = 0.4
static let bleForceAnnounceMinIntervalSeconds: TimeInterval = 0.15
// BCH-01-004: Rate-limiting for subscription-triggered announces
// Prevents rapid enumeration attacks by rate-limiting announce responses
static let bleSubscriptionRateLimitMinSeconds: TimeInterval = 2.0 // Minimum interval between announces per central
static let bleSubscriptionRateLimitBackoffFactor: Double = 2.0 // Exponential backoff multiplier
static let bleSubscriptionRateLimitMaxBackoffSeconds: TimeInterval = 30.0 // Maximum backoff period
static let bleSubscriptionRateLimitWindowSeconds: TimeInterval = 60.0 // Window for tracking subscription attempts
static let bleSubscriptionRateLimitMaxAttempts: Int = 5 // Max attempts before extended cooldown
// Store-and-forward for directed packets at relays
static let bleDirectedSpoolWindowSeconds: TimeInterval = 15.0