what are chaff coins in cryptocurrency?

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I read in several paper about "chaff coins" but I could not find a clear definition for this phenomenon. Does it refer to a specific coin? Is there any "formal" definition for that ?

Reference: https://arxiv.org/abs/1704.04299

Questioner

Posted 2017-10-01T14:16:34.423

Reputation: 906

It refers to the altcoins that no one uses.MCCCS 2017-10-01T14:50:12.050

@MCCCS: Please don't use comments to answer the question. :)Murch 2017-10-01T14:55:03.697

@MCCCS, Would you explain more about that ? e.g. which altcoin called as a chaff coin ?Questioner 2017-10-01T15:35:21.533

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There are over 900 altcoins in this list (https://coinmarketcap.com), and only less than 100 of them are serious money. Others are junk.

MCCCS 2017-10-01T16:04:44.033

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Are you talking about this paper? https://arxiv.org/abs/1704.04299

Nick ODell 2017-10-01T20:50:20.687

@ Nick ODell, Yes, of course, Do you know what does it mean exactly?Questioner 2017-10-02T12:03:29.437

Answers

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The term is used specifically in Monero's ring signature based spending scheme.

Monero transactions do not exactly specify which previous outputs are being spent. Instead, a list of alternative inputs is provided (consisting of the real one, and a number of chaff coins). A ring signature is then used to prove authority to spend from the real one, without revealing which one that is.

This has the advantage of obscuring the transaction graph significantly. It also comes at a very high price - as it means validation cannot use a UTXO set based approach, and must instead maintain an ever-growing database of spent coins to prevent double spending.

Pieter Wuille

Posted 2017-10-01T14:16:34.423

Reputation: 54 032