send entropy in packets, validate entropy in received ACKs

utils/utils.go

@@ -2,6 +2,7 @@ package utils
 
 import (
 	"bytes"
+	"crypto/rand"
 	"io"
 )
 
@@ -123,6 +124,20 @@ func Min(a, b int) int {
 	return b
 }
 
+// RandomBit returns a cryptographically secure random bit (encoded as true / false)
+func RandomBit() (bool, error) {
+	// ToDo: it's probably more efficient to read a bigger slice of random numbers at once and to cache them somewhere
+	b := make([]byte, 1)
+	_, err := rand.Read(b)
+	if err != nil {
+		return false, err
+	}
+	if uint8(b[0])%2 == 0 {
+		return false, nil
+	}
+	return true, nil
+}
+
 // Uint32Slice attaches the methods of sort.Interface to []uint32, sorting in increasing order.
 type Uint32Slice []uint32
 

utils/utils_test.go

@@ -110,6 +110,14 @@ var _ = Describe("Utils", func() {
 		})
 	})
 
+	Context("Rand", func() {
+		It("returns either true or false", func() {
+			val, err := RandomBit()
+			Expect(err).ToNot(HaveOccurred())
+			Expect(val).To(SatisfyAny(Equal(true), Equal(false)))
+		})
+	})
+
 	Context("ReadUintN", func() {
 		It("reads n bytes", func() {
 			m := map[uint8]uint64{