crypto/elliptic: miscalculating points along secp256k1 curve

[gopherbot]

by masterscriptmaker595:

What steps will reproduce the problem?
If possible, include a link to a program on play.golang.org.
1. Use crypto/elliptic with a user-defined curve and use ScalarBaseMult
Example: http://play.golang.org/p/4T0dfjoVnm

What is the expected output?
x: 23960696573610029253367988531088137163395307586261939660421638862381187549638
y: 5176714262835066281222529495396963740342889891785920566957581938958806065714

What do you see instead?
x: 42280923352545849137126817920755343570165861033690210017553292968955371063312
y: 103482896390716835059169134495585006412497735694669345518593957036165264496525

Which compiler are you using (5g, 6g, 8g, gccgo)?
go run

Which operating system are you using?
Win 8

Which version are you using?  (run 'go version')
go version go1.2rc4 windows/amd64

Please provide any additional information below.
The library here seems to get the correct answer:
https://github.com/ThePiachu/Golang-Koblitz-elliptic-curve-DSA-library/blob/master/bitelliptic/bitelliptic.go

[robpike]

Comment 1:

Labels changed: added priority-later, removed priority-triage.

Owner changed to @agl.

Status changed to Accepted.

[agl]

Comment 2:

Please note: http://golang.org/pkg/crypto/elliptic/#Curve, "A Curve represents a
short-form Weierstrass curve with a=-3".
secp256k1 does not meet that requirement.

Status changed to Invalid.