Which bcrypt cost to use for 2018? - go

Question

Update
Actually it seems the benchmark was incorrectly setup I have followed the resource shared by user #Luke Joshua Park and now it works.
package main
import "testing"
func benchmarkBcrypt(i int, b *testing.B){
for n:= 0; n < b.N; n++ {
HashPassword("my pass", i)
}
}
func BenchmarkBcrypt9(b *testing.B){
benchmarkBcrypt(9, b)
}
func BenchmarkBcrypt10(b *testing.B){
benchmarkBcrypt(10, b)
}
func BenchmarkBcrypt11(b *testing.B){
benchmarkBcrypt(11, b)
}
func BenchmarkBcrypt12(b *testing.B){
benchmarkBcrypt(12, b)
}
func BenchmarkBcrypt13(b *testing.B){
benchmarkBcrypt(13, b)
}
func BenchmarkBcrypt14(b *testing.B){
benchmarkBcrypt(14, b)
}
Output:
BenchmarkBcrypt9-4 30 39543095 ns/op
BenchmarkBcrypt10-4 20 79184657 ns/op
BenchmarkBcrypt11-4 10 158688315 ns/op
BenchmarkBcrypt12-4 5 316070133 ns/op
BenchmarkBcrypt13-4 2 631838101 ns/op
BenchmarkBcrypt14-4 1 1275047344 ns/op
PASS
ok go-playground 10.670s
Old incorrect benchmark
I have a small set on benchmark test in golang and am curios of to what is a recommended bcrypt cost to use as of May 2018.
This is my benchrmark file:
package main
import "testing"
func BenchmarkBcrypt10(b *testing.B){
HashPassword("my pass", 10)
}
func BenchmarkBcrypt12(b *testing.B){
HashPassword("my pass", 12)
}
func BenchmarkBcrypt13(b *testing.B){
HashPassword("my pass", 13)
}
func BenchmarkBcrypt14(b *testing.B){
HashPassword("my pass", 14)
}
func BenchmarkBcrypt15(b *testing.B){
HashPassword("my pass", 15)
}
and this is HashPassword() func inside main.go:
import (
"golang.org/x/crypto/bcrypt"
)
func HashPassword(password string, cost int) (string, error) {
bytes, err := bcrypt.GenerateFromPassword([]byte(password), cost)
return string(bytes), err
}
The current output is:
go test -bench=.
BenchmarkBcrypt10-4 2000000000 0.04 ns/op
BenchmarkBcrypt12-4 2000000000 0.16 ns/op
BenchmarkBcrypt13-4 2000000000 0.32 ns/op
BenchmarkBcrypt14-4 1 1281338532 ns/op
BenchmarkBcrypt15-4 1 2558998327 ns/op
PASS
It seems that for a bcrypt with cost of 13 the time it takes is 0.32 nanoseconds, and for cost 14 the time is 1281338532ns or ~1.2 seconds
Which I believe is too much. What do is the best bcrypt cost to use for the current year 2018.

Answer 1

I'm not certain what's going on with Benchmark here. If you just time these, it works fine, and you can work out the right answer for you.
package main
import (
"golang.org/x/crypto/bcrypt"
"time"
)
func main() {
cost := 10
start := time.Now()
bcrypt.GenerateFromPassword([]byte("password"), cost)
end := time.Now()
print(end.Sub(start) / time.Millisecond)
}
For a work factor of 10, on my MacBook Pro I get 78ms. A work factor of 11 is 154ms, and 12 is 334ms. So we're seeing roughly doubling, as expected.
The goal is not a work factor; it's a time. You want as long as you can live with. In my experience (mostly working on client apps), 80-100ms is a nice target because compared to a network request it's undetectable to the user, while being massive in terms of brute-force attacks (so the default of 10 is ideal for my common use).
I generally avoid running password stretching on servers if I can help it, but this scale can be a reasonable trade-off between server impact and security. Remember that attackers may use something dramatically faster than a MacBook Pro, and may use multiple machines in parallel; I pick 80-100ms because of user experience trade-offs. (I perform password stretching on the client when I can get away with it, and then apply a cheap hash like SHA-256 on the server.)
But if you don't do this very often, or can spend more time on it, then longer is of course better, and on my MacBook Pro a work factor of 14 is about 1.2s, which I would certainly accept for some purposes.
But there's a reason that 10 is still the default. It's not an unreasonable value.