Oddbean new post about | logout
▲ ▼
mleku | 3 months ago (raw) | root | parent | reply | flag 
 it's 1 bit missing, claude is wrong

i literally was getting ~50% error on an ECDH test that used secrets that weren't checked for being even pubkeys

as soon as i made it check for 2 only, fixed
▲ ▼
cloud fodder | 3 months ago (raw) | root | parent | reply | flag 
 now i need to check if go-nostr keygen does it right.. thats typically what ive been using..
▲ ▼
mleku | 3 months ago (raw) | root | parent | reply | flag 
 spoiler alert: it doesn't check

i just never encountered this before, because it looks like most generators check for a 2 key and either invert it or reject it

it's not specified in either nip-04 or bip-340 except obliquely and not explicitly

you can't get around it, claude is wrong, the ECDH computation makes two different keys depending on whether it's an odd or even Y
▲ ▼
cloud fodder | 3 months ago (raw) | root | parent | reply | flag 
 huh, but it has the pubkey, why wouldnt it be able to know its even or odd when computing shared secret?  im missing something here..
▲ ▼
mleku | 3 months ago (raw) | root | parent | reply | flag 
 it's not possible for the sender to know the extra bit, they pick the wrong one, the receiver at best could send back a reply "wrong bit"
▲ ▼
cloud fodder | 3 months ago (raw) | root | parent | reply | flag 
 damn 🌋🌊
▲ ▼
ChipTuner | 3 months ago (raw) | root | parent | reply | flag 
 I think it's time to hopefully ask @fiatjaf and maybe @JeffG 

Something seems really wrong. This is nothing that's come up in my tests before. Were all missing something?? This is a huge deal! I beleive this would be part of an EC twist vulnerability...
▲ ▼
ChipTuner | 3 months ago (raw) | root | parent | reply | flag 
 CC @@Magister Michael Dilger M.Sc. @Vitor Pamplona
▲ ▼
mleku | 3 months ago (raw) | root | parent | reply | flag 
 i wasn't aware of what this exactly means, it's not a vulnerability, it's a bug that surely is killing nostr adoption because everyon expects DMs to work, but they obviously can't work without that extra bit

if my dm partners are mostly different sign keys to me, we can't use it
▲ ▼
Magister Michael Dilger M.Sc. | 3 months ago (raw) | root | parent | reply | flag 
 BIP-340 specifies choosing the 02.  Look at the section "Implicit Y coordinates"
▲ ▼
mleku | 3 months ago (raw) | root | parent | reply | flag 
 so using code that doesn't check for it is wrong

go read some source code of nostr libraries again with regard to key generation

i'm not gonna pretend i checked the javascript or rust libraries, as i hate both of these languages but the Go libraries DO NOT CHECK

just write a short piece of code generating new keys and then use two of them to make an ECDH key both ways

then you'll know if the library is doing it right