Subject: [quicwg/base-drafts] ECN attacks (#2163)

From: ekr <[email-masked]>
Date: Thu, 13 Dec 2018 14:11:10 -0800

S 21.7 

```
An on-the-side attacker can duplicate and send packets with modified ECN
codepoints to affect the sender's rate.  If duplicate packets are discarded by a
receiver, an off-path attacker will need to race the duplicate packet against
the original to be successful in this attack.  Therefore, QUIC receivers ignore
ECN codepoints set in duplicate packets (see {{ecn}}).
```

This could use more elaboration. As written, it seems like if you win the race (which you might like half the time) then you will succeed in the attack. Is that true?

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From: Martin Thomson <[email-masked]>
Date: Thu, 13 Dec 2018 21:00:48 -0800

Yes, the winner of a race can reduce the congestion window or maybe prevent it from being reduced.

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