Merge pull request #2014 from hashicorp/f-secure-rand

Use a cryptographically secure seed

lib/rand.go

@@ -1,6 +1,9 @@
 package lib
 
 import (
+	crand "crypto/rand"
+	"math"
+	"math/big"
 	"math/rand"
 	"sync"
 	"time"
@@ -8,11 +11,24 @@ import (
 
 var (
 	once sync.Once
+
+	// SeededSecurely is set to true if a cryptographically secure seed
+	// was used to initialize rand.  When false, the start time is used
+	// as a seed.
+	SeededSecurely bool
 )
 
 // SeedMathRand provides weak, but guaranteed seeding, which is better than
 // running with Go's default seed of 1.  A call to SeedMathRand() is expected
 // to be called via init(), but never a second time.
 func SeedMathRand() {
-	once.Do(func() { rand.Seed(time.Now().UTC().UnixNano()) })
+	once.Do(func() {
+		n, err := crand.Int(crand.Reader, big.NewInt(math.MaxInt64))
+		if err != nil {
+			rand.Seed(time.Now().UTC().UnixNano())
+			return
+		}
+		rand.Seed(n.Int64())
+		SeededSecurely = true
+	})
 }