1 2018-01-29 18:42:49 <ProfMac> when I sign a message, is there a sha256 digest that can be recovered from the signature?
 2 2018-01-29 18:45:34 <arubi> only the signature?
 3 2018-01-29 18:46:51 <ProfMac> Yes, only the signature.  I am deciding whether to explicitly include the sha256 in a report.
 4 2018-01-29 18:46:53 <arubi> ProfMac, if you have the signature, the k value and the private key, then you can know what digest that was signedwas.  but not with just the sig
 5 2018-01-29 18:47:34 <ProfMac> No, signed with someone else's public key, then reported publicly.
 6 2018-01-29 18:48:11 <arubi> there's nothing you can recover from just a signature.  basically almost any two numbers are a valid signature
 7 2018-01-29 18:48:24 <ProfMac> It is a matter of how succinct I can make my report.
 8 2018-01-29 18:48:37 <ProfMac> Thanks.
 9 2018-01-29 18:48:51 <arubi> np
10 2018-01-29 18:50:16 <ProfMac> *both the other person's signing address as well as the signature are reported.
11 2018-01-29 18:54:10 <arubi> even if it were the pubkey, I don't think you could recover z
12 2018-01-29 18:54:29 <arubi> you'd get some point that is z*G, now how do you go back to z? :)
13 2018-01-29 18:55:50 <arubi> s/were/had/ ..
14 2018-01-29 18:56:04 <arubi> err, no.  "even if it were" is right
15 2018-01-29 20:26:02 <ghost43> how should a txn's witness be parsed if the parent txn's scriptPubKey is not available? do I have no way of determining witness program version for example?
16 2018-01-29 20:27:48 <gmaxwell> ghost43: a witness program is all just data pushes.  Generally you should treat it as totally opaque.
17 2018-01-29 20:28:11 <ghost43> gmaxwell: so I do need the scriptPubKey it spends?
18 2018-01-29 20:28:25 <gmaxwell> also this channel is basically dead, I wouldn't recommend asking any questions here and expecting answers.
19 2018-01-29 20:29:06 <gmaxwell> ghost43: Well, need for what?  FWIW, this isn't unique to segwit-- any script pubkey could contain more or less arbritary stuff, what looks like a pubkey and signature might be something else completely.
20 2018-01-29 20:29:12 <ghost43> where should I ask? #bitcoin is usually full of casual talk; so then #bitcoin-core-dev?? seems off-topic there
21 2018-01-29 20:29:32 <gmaxwell> I'd recommend stackoverflow for this sort of question.
22 2018-01-29 20:29:54 <gmaxwell> And tech questions are welcome in #bitcoin fwiw, most of the ops there will tell the casual talk to quiet down when someone has a serious question.