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

  • It refers to the altcoins that no one uses.
    – MCCCS
    Oct 1, 2017 at 14:50
  • @MCCCS: Please don't use comments to answer the question. :)
    – Murch
    Oct 1, 2017 at 14:55
  • @MCCCS, Would you explain more about that ? e.g. which altcoin called as a chaff coin ?
    – Questioner
    Oct 1, 2017 at 15:35
  • 1
    There are over 900 altcoins in this list (coinmarketcap.com), and only less than 100 of them are serious money. Others are junk.
    – MCCCS
    Oct 1, 2017 at 16:04
  • 2
    Are you talking about this paper? arxiv.org/abs/1704.04299
    – Nick ODell
    Oct 1, 2017 at 20:50

1 Answer 1


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.

  • If it doesn't reveal which one is spent, then how can we know it isn't a double-spend?
    – user253751
    Apr 22, 2021 at 11:47

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