106 lines
3.0 KiB
Go
106 lines
3.0 KiB
Go
package configfile
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import (
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"log"
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"math"
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"os"
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"golang.org/x/crypto/scrypt"
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"github.com/rfjakob/gocryptfs/internal/cryptocore"
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"github.com/rfjakob/gocryptfs/internal/tlog"
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)
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const (
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// ScryptDefaultLogN is the default scrypt logN configuration parameter.
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// logN=16 (N=2^16) uses 64MB of memory and takes 4 seconds on my Atom Z3735F
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// netbook.
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ScryptDefaultLogN = 16
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// From RFC7914, section 2:
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// At the current time, r=8 and p=1 appears to yield good
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// results, but as memory latency and CPU parallelism increase, it is
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// likely that the optimum values for both r and p will increase.
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// We reject all lower values that we might get through modified config files.
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scryptMinR = 8
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scryptMinP = 1
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// logN=10 takes 6ms on a Pentium G630. This should be fast enough for all
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// purposes. We reject lower values.
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scryptMinLogN = 10
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// We always generate 32-byte salts. Anything smaller than that is rejected.
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scryptMinSaltLen = 32
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)
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// ScryptKDF is an instance of the scrypt key deriviation function.
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type ScryptKDF struct {
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// Salt is the random salt that is passed to scrypt
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Salt []byte
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// N: scrypt CPU/Memory cost parameter
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N int
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// R: scrypt block size parameter
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R int
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// P: scrypt parallization paramter
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P int
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// KeyLen is the output data length
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KeyLen int
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}
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// NewScryptKDF returns a new instance of ScryptKDF.
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func NewScryptKDF(logN int) ScryptKDF {
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var s ScryptKDF
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s.Salt = cryptocore.RandBytes(cryptocore.KeyLen)
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if logN <= 0 {
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s.N = 1 << ScryptDefaultLogN
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} else {
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s.N = 1 << uint32(logN)
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}
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s.R = 8 // Always 8
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s.P = 1 // Always 1
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s.KeyLen = cryptocore.KeyLen
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return s
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}
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// DeriveKey returns a new key from a supplied password.
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func (s *ScryptKDF) DeriveKey(pw string) []byte {
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s.validateParams()
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k, err := scrypt.Key([]byte(pw), s.Salt, s.N, s.R, s.P, s.KeyLen)
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if err != nil {
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log.Panicf("DeriveKey failed: %v", err)
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}
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return k
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}
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// LogN - N is saved as 2^LogN, but LogN is much easier to work with.
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// This function gives you LogN = Log2(N).
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func (s *ScryptKDF) LogN() int {
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return int(math.Log2(float64(s.N)) + 0.5)
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}
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// validateParams checks that all parameters are at or above hardcoded limits.
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// If not, it exists with an error message.
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// This makes sure we do not get weak parameters passed through a
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// rougue gocryptfs.conf.
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func (s *ScryptKDF) validateParams() {
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minN := 1 << scryptMinLogN
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if s.N < minN {
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tlog.Fatal.Println("Fatal: scryptn below 10 is too low to make sense")
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os.Exit(1)
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}
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if s.R < scryptMinR {
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tlog.Fatal.Printf("Fatal: scrypt parameter R below minimum: value=%d, min=%d", s.R, scryptMinR)
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os.Exit(1)
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}
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if s.P < scryptMinP {
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tlog.Fatal.Printf("Fatal: scrypt parameter P below minimum: value=%d, min=%d", s.P, scryptMinP)
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os.Exit(1)
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}
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if len(s.Salt) < scryptMinSaltLen {
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tlog.Fatal.Printf("Fatal: scrypt salt length below minimum: value=%d, min=%d", len(s.Salt), scryptMinSaltLen)
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os.Exit(1)
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}
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if s.KeyLen < cryptocore.KeyLen {
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tlog.Fatal.Printf("Fatal: scrypt parameter KeyLen below minimum: value=%d, min=%d", len(s.Salt), cryptocore.KeyLen)
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os.Exit(1)
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}
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}
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