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package configfile
import (
"log"
"math"
"os"
"golang.org/x/crypto/scrypt"
"github.com/rfjakob/gocryptfs/internal/cryptocore"
"github.com/rfjakob/gocryptfs/internal/tlog"
)
const (
// ScryptDefaultLogN is the default scrypt logN configuration parameter.
// 1 << 16 uses 64MB of memory,
// takes 4 seconds on my Atom Z3735F netbook
ScryptDefaultLogN = 16
)
// ScryptKDF is an instance of the scrypt key deriviation function.
type ScryptKDF struct {
Salt []byte
N int
R int
P int
KeyLen int
}
// NewScryptKDF returns a new instance of ScryptKDF.
func NewScryptKDF(logN int) ScryptKDF {
var s ScryptKDF
s.Salt = cryptocore.RandBytes(cryptocore.KeyLen)
if logN <= 0 {
s.N = 1 << ScryptDefaultLogN
} else {
if logN < 10 {
tlog.Fatal.Println("Error: scryptn below 10 is too low to make sense. Aborting.")
os.Exit(1)
}
s.N = 1 << uint32(logN)
}
s.R = 8 // Always 8
s.P = 1 // Always 1
s.KeyLen = cryptocore.KeyLen
return s
}
// DeriveKey returns a new key from a supplied password.
func (s *ScryptKDF) DeriveKey(pw string) []byte {
k, err := scrypt.Key([]byte(pw), s.Salt, s.N, s.R, s.P, s.KeyLen)
if err != nil {
log.Panicf("DeriveKey failed: %v", err)
}
return k
}
// LogN - N is saved as 2^LogN, but LogN is much easier to work with.
// This function gives you LogN = Log2(N).
func (s *ScryptKDF) LogN() int {
return int(math.Log2(float64(s.N)) + 0.5)
}
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