How to recover ECDSA public key from the signature?
I know that all is need is a hash of the unsigned message and signature.
But may be there is some detailed method for to calculate ECDSA public key?
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do want to sign a message, or do you want to extract pubkey from an already signed tx?– pebwindkraftCommented Oct 20, 2017 at 7:57
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i interested about extraction publickey from already signed tx– Denis LeonovCommented Oct 20, 2017 at 8:02
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@HughMarstonHefner Are you asking about transactions, or you are looking for a general way of deriving an ECDSA public key from a given signature and message?– sr_giCommented Oct 20, 2017 at 15:22
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@sr-gi i pointed out very clearly– Denis LeonovCommented Oct 20, 2017 at 22:52
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That may be the way then: crypto.stackexchange.com/questions/18105/…– sr_giCommented Oct 20, 2017 at 22:55
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1 Answer
when looking at a signed (P2PKH) tx, the signature looks like this:
483045022100A428348FF55B2B59BC55DDACB1A00F4ECDABE282707BA5185D39FE9CDF05D7F0022074232DAE76965B6311CEA2D9E5708A0F137F4EA2B0E36D0818450C67C9BA259D0121025F95E8A33556E9D7311FA748E9434B333A4ECFB590C773480A196DEAB0DEDEE1
This can be further split into two parts:
signature: 483045022100A428348FF55B2B59BC55DDACB1A00F4ECDABE282707BA5185D39FE9CDF05D7F0022074232DAE76965B6311CEA2D9E5708A0F137F4EA2B0E36D0818450C67C9BA259D01
pubkey: 21025F95E8A33556E9D7311FA748E9434B333A4ECFB590C773480A196DEAB0DEDEE1
and further looks like this in detail (with address for pubkey at the end):
##################################################################
48: OP_DATA_0x48: push hex 48 (decimal 72) bytes as data
30: OP_SEQUENCE_0x30: type tag indicating SEQUENCE, begin sigscript
45: OP_LENGTH_0x45: length of R + S
02: OP_INT_0x02: type tag indicating INTEGER
21: OP_LENGTH_0x21: this is SIG R
00A428348FF55B2B:59BC55DDACB1A00F
4ECDABE282707BA5:185D39FE9CDF05D7
F0
02: OP_INT_0x02: type tag indicating INTEGER
20: OP_LENGTH_0x20: this is SIG S
74232DAE76965B63:11CEA2D9E5708A0F
137F4EA2B0E36D08:18450C67C9BA259D
01: OP_SIGHASHALL: this terminates the ECDSA signature (ASN1-DER structure)
#########################################################
21: OP_DATA_0x21: type tag indicating LENGTH
02: OP_INT_0x02: type tag indicating INTEGER
5F95E8A33556E9D7:311FA748E9434B33
3A4ECFB590C77348:0A196DEAB0DEDEE1
* This terminates the Public Key (X9.63 COMPRESSED form)
* corresponding bitcoin address is:
1HTNtayFkoBV28wqDygMbW33qSnRjxAuNR
answered Oct 20, 2017 at 8:06
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please tell where is the hash which is need for signature verification with corresponding public key? Commented Oct 20, 2017 at 8:10
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hmmm, I think I don't get it.... the hash is constructed before signing, or can be reconstructed, as described here bitcoin.stackexchange.com/questions/60051/… - achow explained it with another link. So the hash is not included in the tx itself. Commented Oct 20, 2017 at 8:17
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2Hmm I don't get the answer. The question is about key recovery while the answer talks about signatures without key recovery.– Jus12Commented Dec 27, 2017 at 5:20
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maybe I need some help then... the first line in the question says: "How to recover ECDSA public key from the signature?", I thought I'd show how to get to the pubkey from the signature... There it is in X9.63 (compressed) format. Is op looking for a different format, like the p,r,s and z format? Commented Dec 27, 2017 at 7:41
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late, but anyhow: based on the comment from @Jus12, I reviewed some other posts on ECDSA, and found this link, which is also referenced in some other threads: bitcointalk.org/index.php?topic=6430.0 - it shows tht pubkey is included in signature itself, but not implemented in Bitcoin, due to more CPU cycles - and it would probably require a hardfork. Commented Mar 2, 2018 at 22:58