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Date: Thu, 9 Jul 2015 03:27:43 +0100
From: denis bider <>
Subject: Re: [PHC] Memory-hard proof of work with fast verification (CPU Hash)

It is generally a good idea for the network to defend itself against DoS by requiring incoming node connections to submit a costly proof of work A that's cheap to verify, just to accept the connection. If this measure is effective, it allows use of proof of work B that's costlier to verify for actual block verification. If a node submits an invalid block, disconnect it and require it to go through proof of work A again if it wants to re-connect.

Of course, this requires some proof of work A that's cheap to verify and still not trivializable. But the incentives to attack proof of work A (which merely gates connections) are much different to incentives to attack proof of work B (which underpins the currency).

-----Original Message-----  From: Zooko Wilcox-O'Hearn  Sent: Wednesday, July 8, 2015 15:27  To:  Subject: Re: [PHC] Memory-hard proof of work with fast verification (CPU  Hash)    Dear Bill Cox and Solar Designer:   Thanks for the useful conversation.   On Tue, Jul 7, 2015 at 10:29 PM, Bill Cox <>  wrote: > > One more concern is a possible DDoS attack on the network.   Publishing > 1,000's of fake solutions to blocks per second that require the  entire > network to debunk them with a very computationally expensive  verification > would be bad.  I read about that DDoS problem somewhere recently...  can't > remember if it was the Argon2 paper or somewhere else.   Hm, that's a good point. I haven't thought this one all the way through. I don't know how to assign a budget to this one, other than "the cheaper verification is the better".

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