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Edit: nevermind https://www.getmonero.org/resources/moneropedia/ringsignatures.html https://www.getmonero.org/resources/moneropedia/ringsignatur... cleared it u

by KMag 5y ago

Edit: nevermind https://www.getmonero.org/resources/moneropedia/ringsignatures.html https://www.getmonero.org/resources/moneropedia/ringsignatur... cleared it up. Zero-knowledge proofs/cryptographic accumulators are used to verify each coin is spent at most once. Any of 11 coins could have been spent, each owned by a different single key. For some reason, I thought Monero was basically ZCash plus using ring signatures to make traffic analysis much more difficult even if the zk proof system were broken. I was completely mistaken. Edit 2: Sorry droffel, I wasn't fast enough editing away my old understanding of how it worked and asking what I was missing. Thanks for the explanation.

droffel 5y ago
The piece you are missing is called the Key Image. The key image can be thought of as a fingerprint/hash (one way function) of the true spender, and is always produced when the true spender signs the transaction. Signing the transaction with any of the decoy keys will not produce a valid key image, and therefore they are not able to spend the funds (or see their amount). This key image is also used to verify that transactions aren't being spent twice - despite not knowing which input in a ring is actually being spent, a transaction with a key image that has never been used before guarantees that it hasn't been spent in the past.