roll: use crypto/rand, D&D is serious business

1 files changed, 12 insertions, 5 deletions

diff --git a/roll.go b/roll.go
index f5f9b67..414b0d2 100644
--- a/roll.go
+++ b/roll.go
@@ -1,19 +1,27 @@
-/* Copyright (C) 2011, 2013-2014 Luke Shumaker <lukeshu@sbcglobal.net> */
+/* Copyright (C) 2011, 2013-2014, 2017 Luke Shumaker <lukeshu@sbcglobal.net> */
 package main
 
 import (
+	"crypto/rand"
 	"fmt"
-	"math/rand"
+	"math/big"
 	"os"
 	"regexp"
 	"strconv"
-	"time"
 )
 
 func usage() {
 	fmt.Printf("Arguments are in the format [<COUNT>]d<SIZE>[+<MOD>]\n")
 }
 
+func rollDie(size int) int {
+	num, err := rand.Int(rand.Reader, big.NewInt(int64(size)))
+	if err != nil {
+		panic(err)
+	}
+	return int(num.Int64()) + 1
+}
+
 func roll(input string) {
 	parser := regexp.MustCompile("^([0-9]*)d([0-9]+)([+-][0-9]+)?$")
 	parts := parser.FindStringSubmatch(input)
@@ -33,7 +41,7 @@ func roll(input string) {
 
 	total := 0
 	for i := 0; i < dice; i++ {
-		v := rand.Intn(die_size) + 1
+		v := rollDie(die_size)
 		fmt.Printf("%d+", v)
 		total += v
 	}
@@ -42,7 +50,6 @@ func roll(input string) {
 }
 
 func main() {
-	rand.Seed(time.Now().UTC().UnixNano())
 	if len(os.Args) == 1 {
 		usage()
 	}