Output keys are 256 bits public keys. They should be unique.
Are there any duplicate output keys ?
What happens if there is any ? Is it a double spend ?
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Here are the duplicates for block in range(1,1500000), with the count:
- 8837 9b2e4c0281c0b02e7c53291a94d1d0cbff8883f8024f5142ee494ffbbd088071
- 70 2a74a3c4c36d32e95633d44ba9a7b8188297b2ac91afecab826b86fabaa70916
- 8 362da94d535b602c1ea909627da4ffb35bf01dd4689698f6393f3a5e995973b8
- 7 0ad4bab9288ecbb1066ece2ea3fba29a013301cfa1d472da7467876635996a34
- 6 71420acc3b5e7b3aa5405fdf06cc435c37339f8efd08c7033c4a000e0d4804b7
- 6 ad0f4a8bb1849166d5e75c46f52b8390629f093cf100f8221f9de8f00f00f80a
- 5 944e84a00c2e47b8ab6c1ed4e7d5325449940bd7d9947c321f2f78c6f67266cc
- 5 52d128bc9913d5ee8b702c37609917c2357b2f587e5de5622348a3acd718e5d6
- 4 88883ef499326c4344935c57f088758e1370a80ab757d45e0e09413485542f3b
- 3 21242bd2219db8651fbd553339fae003d05b1c01b20424554725bd8e7834ad11
- 3 42e782ea6c9b43d2fc101bf31db45847e2a99f91b596db1afe4851b63bdfa7d6
- 3 b8ed916c56b3a99c9cdf22c7be7ec4e85587e5d40bc46bf6995313c288ad841e
- 3 a6f70eae9db3e3a06000fc2cbf38d48f236d289b9ca3673e4a6edb5719e970e2
- 2 8d820398c912ca0916e964990fd4a34ab5cda3d4f8ad992dc12fc7ee63cfa0f0
- 2 142076b705ec912288816f0a08da20b64f9907bf99fbce74e39a85a300658191
- 2 7e69fc5c12439bc793ec53993207ea5594ab64e2d148cb81f465c3d88f905b87
- 2 5d397b2a3cb2788a1de2be6632fa2e389b885e59f531d11c51470ae12240f86a
- 2 1b452b4ac6c6419e06181f8c9f0734bd5bb132d8b75b44bbcd07dd8f553acba6
- 2 c574420256922b0783196e42c98156814e61d9ffa87c1262089be1d42e5f0d27
- 2 b10ba13e303cbe9abf7d5d44f1d417727abcc14903a74e071abd652ce1bf76dd
As noted in this reddit thread, the first key (used 8837 times) is also the output key of the coinbase transaction in the genesis block.
Quoting smooth:
No its not a double spend. It is burning coins, so in a sense the opposite of a double spend. Possibly unintended due to a bug, but without knowing who is generating those or why it is impossible to say.
Each key can only be spent once, so out of these 8950 outputs, 8930 are unspendable.
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2Related question, which might be of interest to the reader: monero.stackexchange.com/questions/4163/… – dEBRUYNE♦ Mar 6 '18 at 10:06
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As I've recently stumbled over this issue as well, here's a CSV file that contains all reused pubkeys and their count: reused_pubk.csv
And here also the blocks and transactions where and when they occur (Timestamp, Block, TX Hash): reused_pubk_full.csv
(Both links go to a github repo, if changes occur at some point, use this commit)
It seems that whatever bug was responsible for it has been patched at some time after 2016-10-23 (or the last client updated his wallet software back then).
