crypt/mwords: add misc function to get N random words from wordlist

crypt/mwords/utility.go

@@ -1,6 +1,10 @@
 package mwords
 
-import "math/big"
+import (
+	"math/big"
+	"math/rand"
+	"time"
+)
 
 // bit mask for 11 least significant bits
 var bits0to11 = big.NewInt(0x7FF)
@@ -46,3 +50,20 @@ func isValidEntropy(bits uint) bool {
 	}
 	return true
 }
+
+// RandomWords will return n random words from the wordlist.
+func RandomWords(n uint) []string {
+	// seed RNG
+	rand.Seed(time.Now().UTC().UnixNano())
+
+	// return slice
+	ret := make([]string, n)
+
+	// get n random words
+	for n > 0 {
+		ret[n-1] = mnemonicWords[rand.Int()%Count]
+		n--
+	}
+
+	return ret
+}

crypt/mwords/utility_test.go

@@ -2,6 +2,8 @@ package mwords
 
 import (
 	"testing"
+
+	"cpl.li/go/cryptor/tests"
 )
 
 func TestEntropyBits(t *testing.T) {
@@ -26,3 +28,13 @@ func TestEntropyBits(t *testing.T) {
 		}
 	}
 }
+
+func assertRandomWords(t *testing.T, num uint) {
+	tests.AssertEqual(t, uint(len(RandomWords(num))), num, "invalid word count")
+}
+
+func TestRandomWords(t *testing.T) {
+	for i := uint(0); i < 100; i++ {
+		assertRandomWords(t, i)
+	}
+}