p2p: Use network-dependent timers for inbound inv scheduling #33464

1. 
   mzumsande commented at 5:19 pm on September 23, 2025: contributor

   Currently, NextInvToInbounds schedules each round of inv at the same time for all inbound peers. It’s being done this way because with a separate timer per peer (like it’s done for outbounds), an attacker could do multiple connections to learn about the time a transaction arrived. (#13298).

   However, having a single timer for inbounds of all networks is also an obvious fingerprinting vector: Connecting to a suspected pair of privacy-network and clearnet addresses and observing the inv pattern makes it trivial to confirm or refute that they are the same node.

   This PR changes it such that a separate timer is used for each network. It uses the existing method from getaddr caching and generalizes it to be saved in a new field m_network_key in CNode which will be used for both getaddr caching and inv scheduling, and can also be used for any future anti-fingerprinting measures.

2. net: use generic network key for addrcache

   The generic key can also be used in other places
   where behavior between different network identities should
   be uncorrelated to avoid fingerprinting.
   This also changes RANDOMIZER_ID - since it is not
   being persisted to disk, there are no compatibility issues.

   94db966a3b
3. p2p: Use different inbound inv timer per network

   Currently nodes schedule their invs to all inbound peers at the same time.
   It is trivial to make use this timing pattern for fingerprinting
   identities on different networks. Using a separate timers for each network will
   make the fingerprinting harder.

   beb75e48ae
4. DrahtBot added the label P2P on Sep 23, 2025
5. 
   DrahtBot commented at 5:19 pm on September 23, 2025: contributor

   The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

   Code Coverage & Benchmarks

   For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/33464.

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   ACK	danielabrozzoni

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6. mzumsande marked this as ready for review on Sep 23, 2025
7. 
   danielabrozzoni commented at 4:42 pm on September 25, 2025: contributor

   tACK beb75e48ae1d5771932f427a490c7e1b6c1720d3

   I tested locally by adding a log line, and checking that different networks schedule different inv times:

    0diff --git a/src/net_processing.cpp b/src/net_processing.cpp
    1index f5f04c7a17..fec1cfcb6b 100644
    2--- a/src/net_processing.cpp
    3+++ b/src/net_processing.cpp
    4@@ -5716,6 +5716,7 @@ bool PeerManagerImpl::SendMessages(CNode* pto)
    5                     fSendTrickle = true;
    6                     if (pto->IsInboundConn()) {
    7                         tx_relay->m_next_inv_send_time = NextInvToInbounds(current_time, INBOUND_INVENTORY_BROADCAST_INTERVAL, pto->m_network_key);
    8+                        LogInfo("Scheduling next inv send time for inbound peer on network %d at time %d", pto->m_network_key, tx_relay->m_next_inv_send_time);
    9                     } else {
   10                         tx_relay->m_next_inv_send_time = current_time + m_rng.rand_exp_duration(OUTBOUND_INVENTORY_BROADCAST_INTERVAL);
   11                     }
   

    0$ tail -f ~/.bitcoin/debug.log | grep "Scheduling next inv send time"
    12025-09-25T14:14:09Z Scheduling next inv send time for inbound peer on network 2336814389803672515 at time 1758809657846106us
    22025-09-25T14:14:09Z Scheduling next inv send time for inbound peer on network 2336814389803672515 at time 1758809657846106us
    32025-09-25T14:14:09Z Scheduling next inv send time for inbound peer on network 2336814389803672515 at time 1758809657846106us
    42025-09-25T14:14:09Z Scheduling next inv send time for inbound peer on network 2336814389803672515 at time 1758809657846106us
    52025-09-25T14:14:09Z Scheduling next inv send time for inbound peer on network 2336814389803672515 at time 1758809657846106us
    62025-09-25T14:14:09Z Scheduling next inv send time for inbound peer on network 2336814389803672515 at time 1758809657846106us
    72025-09-25T14:14:09Z Scheduling next inv send time for inbound peer on network 2336814389803672515 at time 1758809657846106us
    82025-09-25T14:14:09Z Scheduling next inv send time for inbound peer on network 2336814389803672515 at time 1758809657846106us
    92025-09-25T14:14:09Z Scheduling next inv send time for inbound peer on network 2336814389803672515 at time 1758809657846106us
   102025-09-25T14:14:09Z Scheduling next inv send time for inbound peer on network 2336814389803672515 at time 1758809657846106us
   112025-09-25T14:14:09Z Scheduling next inv send time for inbound peer on network 2336814389803672515 at time 1758809657846106us
   122025-09-25T14:14:09Z Scheduling next inv send time for inbound peer on network 2336814389803672515 at time 1758809657846106us
   132025-09-25T14:14:09Z Scheduling next inv send time for inbound peer on network 406641846476317050 at time 1758809650020936us
   142025-09-25T14:14:09Z Scheduling next inv send time for inbound peer on network 406641846476317050 at time 1758809650020936us
   152025-09-25T14:14:09Z Scheduling next inv send time for inbound peer on network 406641846476317050 at time 1758809650020936us
   162025-09-25T14:14:09Z Scheduling next inv send time for inbound peer on network 406641846476317050 at time 1758809650020936us
   172025-09-25T14:14:09Z Scheduling next inv send time for inbound peer on network 406641846476317050 at time 1758809650020936us
   182025-09-25T14:14:09Z Scheduling next inv send time for inbound peer on network 406641846476317050 at time 1758809650020936us
   

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mzumsande DrahtBot danielabrozzoni

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