1 files changed, 57 insertions, 0 deletions
diff --git a/internal/configfile/kdf.go b/internal/configfile/kdf.go
new file mode 100644
index 0000000..f1a7a40
--- /dev/null
+++ b/internal/configfile/kdf.go
@@ -0,0 +1,57 @@
+package configfile
+
+import (
+	"fmt"
+	"math"
+	"os"
+
+	"golang.org/x/crypto/scrypt"
+
+	"github.com/rfjakob/gocryptfs/internal/cryptocore"
+)
+
+const (
+	// 1 << 16 uses 64MB of memory,
+	// takes 4 seconds on my Atom Z3735F netbook
+	ScryptDefaultLogN = 16
+)
+
+type scryptKdf struct {
+	Salt   []byte
+	N      int
+	R      int
+	P      int
+	KeyLen int
+}
+
+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 {
+			fmt.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
+}
+
+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 {
+		panic(fmt.Sprintf("DeriveKey failed: %s", err.Error()))
+	}
+	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)
+}