coder · deansheather · Aug 21, 2025 · Aug 20, 2025 · ethanndickson · Aug 21, 2025
diff --git a/cryptorand/numbers.go b/cryptorand/numbers.go
@@ -47,6 +47,12 @@ func Int63() (int64, error) {
 	return rng.Int63(), cs.err
 }
 
+// Int63n returns a non-negative integer in [0,maxVal) as an int64.
+func Int63n(maxVal int64) (int64, error) {
+	rng, cs := secureRand()
+	return rng.Int63n(maxVal), cs.err
+}
+
 // Intn returns a non-negative integer in [0,maxVal) as an int.
 func Intn(maxVal int) (int, error) {
 	rng, cs := secureRand()

diff --git a/cryptorand/numbers_test.go b/cryptorand/numbers_test.go
@@ -19,6 +19,27 @@ func TestInt63(t *testing.T) {
 	}
 }
 
+func TestInt63n(t *testing.T) {
+	t.Parallel()
+
+	for i := 0; i < 20; i++ {
+		v, err := cryptorand.Int63n(100)
+		require.NoError(t, err, "unexpected error from Int63n")
+		t.Logf("value: %v <- random?", v)
+		require.GreaterOrEqual(t, v, int64(0), "values must be positive")
+		require.Less(t, v, int64(100), "values must be less than 100")
+	}
+
+	// Ensure Int63n works for int larger than 32 bits
+	_, err := cryptorand.Int63n(1 << 35)
+	require.NoError(t, err, "expected Int63n to work for 64-bit int")
+
+	// Expect a panic if max is negative
+	require.PanicsWithValue(t, "invalid argument to Int63n", func() {
+		cryptorand.Int63n(0)
+	})
+}
+
 func TestIntn(t *testing.T) {
 	t.Parallel()
 

@@ -136,8 +136,8 @@ func (p *tallymanPublisher) Start() error {
 	if p.initialDelay <= 0 {
 		// Pick a random time between tallymanPublishInitialMinimumDelay and
 		// tallymanPublishInterval.
-		maxPlusDelay := int(tallymanPublishInterval - tallymanPublishInitialMinimumDelay)
-		plusDelay, err := cryptorand.Intn(maxPlusDelay)
+		maxPlusDelay := tallymanPublishInterval - tallymanPublishInitialMinimumDelay
+		plusDelay, err := cryptorand.Int63n(int64(maxPlusDelay))
 		if err != nil {
 			return xerrors.Errorf("could not generate random start delay: %w", err)
 		}