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-rw-r--r--internal/configfile/scrypt.go63
1 files changed, 53 insertions, 10 deletions
diff --git a/internal/configfile/scrypt.go b/internal/configfile/scrypt.go
index 31bcbe4..e1fbf15 100644
--- a/internal/configfile/scrypt.go
+++ b/internal/configfile/scrypt.go
@@ -13,17 +13,34 @@ import (
const (
// ScryptDefaultLogN is the default scrypt logN configuration parameter.
- // 1 << 16 uses 64MB of memory,
- // takes 4 seconds on my Atom Z3735F netbook
+ // logN=16 (N=2^16) uses 64MB of memory and takes 4 seconds on my Atom Z3735F
+ // netbook.
ScryptDefaultLogN = 16
+ // From RFC7914, section 2:
+ // At the current time, r=8 and p=1 appears to yield good
+ // results, but as memory latency and CPU parallelism increase, it is
+ // likely that the optimum values for both r and p will increase.
+ // We reject all lower values that we might get through modified config files.
+ scryptMinR = 8
+ scryptMinP = 1
+ // logN=10 takes 6ms on a Pentium G630. This should be fast enough for all
+ // purposes. We reject lower values.
+ scryptMinLogN = 10
+ // We always generate 32-byte salts. Anything smaller than that is rejected.
+ scryptMinSaltLen = 32
)
// ScryptKDF is an instance of the scrypt key deriviation function.
type ScryptKDF struct {
- Salt []byte
- N int
- R int
- P int
+ // Salt is the random salt that is passed to scrypt
+ Salt []byte
+ // N: scrypt CPU/Memory cost parameter
+ N int
+ // R: scrypt block size parameter
+ R int
+ // P: scrypt parallization paramter
+ P int
+ // KeyLen is the output data length
KeyLen int
}
@@ -34,10 +51,6 @@ func NewScryptKDF(logN int) ScryptKDF {
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
@@ -48,6 +61,8 @@ func NewScryptKDF(logN int) ScryptKDF {
// DeriveKey returns a new key from a supplied password.
func (s *ScryptKDF) DeriveKey(pw string) []byte {
+ s.validateParams()
+
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)
@@ -60,3 +75,31 @@ func (s *ScryptKDF) DeriveKey(pw string) []byte {
func (s *ScryptKDF) LogN() int {
return int(math.Log2(float64(s.N)) + 0.5)
}
+
+// validateParams checks that all parameters are at or above hardcoded limits.
+// If not, it exists with an error message.
+// This makes sure we do not get weak parameters passed through a
+// rougue gocryptfs.conf.
+func (s *ScryptKDF) validateParams() {
+ minN := 1 << scryptMinLogN
+ if s.N < minN {
+ tlog.Fatal.Println("Fatal: scryptn below 10 is too low to make sense")
+ os.Exit(1)
+ }
+ if s.R < scryptMinR {
+ tlog.Fatal.Printf("Fatal: scrypt parameter R below minimum: value=%d, min=%d", s.R, scryptMinR)
+ os.Exit(1)
+ }
+ if s.P < scryptMinP {
+ tlog.Fatal.Printf("Fatal: scrypt parameter P below minimum: value=%d, min=%d", s.P, scryptMinP)
+ os.Exit(1)
+ }
+ if len(s.Salt) < scryptMinSaltLen {
+ tlog.Fatal.Printf("Fatal: scrypt salt length below minimum: value=%d, min=%d", len(s.Salt), scryptMinSaltLen)
+ os.Exit(1)
+ }
+ if s.KeyLen < cryptocore.KeyLen {
+ tlog.Fatal.Printf("Fatal: scrypt parameter KeyLen below minimum: value=%d, min=%d", len(s.Salt), cryptocore.KeyLen)
+ os.Exit(1)
+ }
+}