Alert fix #1729

1. 
   gavinandresen commented at 2:51 PM on August 27, 2012: contributor

   These commits:

   1. prevents a possible DoS (make nodes waste CPU time checking alert signatures) attack (thanks to Sergio Lerner for finding/reporting)
   2. implement's theymos' suggestion of a non-overrideable alert message, to be used only in case the alert key is compromised.

   Both thoroughly tested by me in a testnet-in-a-box environment:

   Verified that nodes are disconnected/banned if they send too many invalid alerts. Verified that the alert system still works properly when sent valid alerts. Verified that nId=max alerts are ignored unless they match hard-coded values. Verified that nId=max alerts work properly if they do match.

2. Alert system DoS prevention

   This fixes two alert system vulnerabilities found by
   Sergio Lerner; you could send peers unlimited numbers
   of invalid alert message to try to either fill up their
   debug.log with messages and/or keep their CPU busy
   checking signatures.
   
   Fixed by disconnecting/banning peers if they send 10 or more
   bad (invalid/expired/cancelled) alerts.

   d5a52d9b3e
3. Special-case the last alert for alert-key-compromised case

   Hard-code a special nId=max int alert, to be broadcast if the
   alert key is ever compromised. It applies to all versions, never
   expires, cancels all previous alerts, and has a fixed message:
      URGENT: Alert key compromised, upgrade required
   
   Variations are not allowed (ignored), so an attacker with
   the private key cannot broadcast empty-message nId=max alerts.

   ea2fda46c3
4. 
   jgarzik commented at 3:49 PM on August 27, 2012: contributor

   ACK

5. 
   laanwj commented at 3:56 PM on August 27, 2012: member

   ACK

6. in src/main.cpp:None in ea2fda46c3

   2337 | +                nCancel == (maxInt-1) &&
   2338 | +                nMinVer == 0 &&
   2339 | +                nMaxVer == maxInt &&
   2340 | +                setSubVer.empty() &&
   2341 | +                nPriority == maxInt &&
   2342 | +                strStatusBar == "URGENT: Alert key compromised, upgrade required"
   

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   Diapolo commented at 4:02 PM on August 27, 2012:

   Could you add an "!" at the end of the message? Yes a nitpick ;-).

7. gavinandresen merged this on Aug 27, 2012
8. gavinandresen closed this on Aug 27, 2012

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9. owlhooter referenced this in commit 3e86c41be5 on Oct 10, 2018
10. DrahtBot locked this on Sep 8, 2021

Milestone
0.7.0