During blockchain scanning I need to do:
P − Hs(aR)G
with every output in order to determie whether it is mine, or not.
Where in tx_json are P and R stored?
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1 Answer
The full math you have to do is:
D = P - Hs(8aR || i)G, where i is a varint representing the index of the output. You then check whether D matches your main public spend key or any of your subaddress public spend keys. if it does, the output is destined for you.
The output public key P is in the json as vout.target.key. The transaction public key R is not separately listed, so you'll need to parse the extra field in the json and locate the txpubkey subfield.
The txextra field format is documented here: https://cryptonote.org/cns/cns005.txt
It's the "Tx public key" field mentioned in that document that you are interested in.
Also note that to support transactions with multiple subaddress recipients, there is also a new TX_EXTRA_TAG_ADDITIONAL_PUBKEYS field. If this field is present, then you'll need to check each output against the corresponding additional txpubkey listed in that field.
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@jtgrassie Ah oops thanks, missed that P is in there. Why though would the txpubkey R be listed as "tx_hash"?– knacccCommented Mar 21, 2019 at 12:05
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I would like to write python script, which is going through blockchain and for each output it sends P and R to hardware wallet, where I am determining if output is mine or not. So, I can get P from tx_json, but what is the best method for getting R ? How the tx_blob is structured? Commented Mar 21, 2019 at 12:07
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@jtgrassie I'm not sure why you think that. I've messaged you on IRC so you can sanity check me.– knacccCommented Mar 21, 2019 at 12:20
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1Size is a varint - the example is just a quick demo (I didn't bother adding varint decoding). Commented Apr 8, 2019 at 22:25