refactor: remove math/big, fix RNG bias, optimize builds, and bump Go version

go.mod

@@ -1,3 +1,3 @@
 module GoPass
 
-go 1.19
+go 1.25.5

main.go

@@ -5,8 +5,8 @@ package main
 import (
 	"crypto/rand"
 	"fmt"
-	"math/big"
 	"os"
+	"runtime"
 	"strconv"
 	"strings"
 )
@@ -14,8 +14,9 @@ import (
 var allowedCharacters = []rune("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890`~!@#$%^&*()_+[]\\{}|;':,./<>?")
 
 const (
-	Version = "1.3.0"
-	symbols = "`~!@#$%^&*()_+[]\\{}|;':,./<>?"
+	Version   = "1.3.5"
+	symbols   = "`~!@#$%^&*()_+[]\\{}|;':,./<>?"
+	chunkSize = 16 // The size of each chunk of the password to be generated by the worker goroutines
 )
 
 func matchArguments(args []string) string {
@@ -26,11 +27,10 @@ func matchArguments(args []string) string {
 
 	// First argument is special, must be an integer, -v, or -h
 	var size = 0 // Password length
-	err := error(nil)
-	if size, err = strconv.Atoi(args[0]); err == nil { // If first argument is an integer
-	} else if args[0] == "-v" {
+	switch args[0] {
+	case "-v":
 		return "GoPass version " + Version
-	} else if args[0] == "-h" {
+	case "-h":
 		return "GoPass - A simple password generator written in Go\n" +
 			"Usage: gopass [length] [disallowed characters] [optional remove symbols -s]\n" +
 			"     Example: gopass 16\n" +
@@ -38,16 +38,23 @@ func matchArguments(args []string) string {
 			"     Example: gopass 16 -s\n" +
 			"\nFor help (this output): gopass -h\n" +
 			"For version: gopass -v\n"
+	default:
+		var err error
+		size, err = strconv.Atoi(args[0])
+		if err != nil {
+			return "Invalid first argument (\"" + args[0] + "\") supplied! (Type gopass -h for help)"
+		}
 	}
 
 	for i := 1; i < len(args); i++ {
 		v := args[i]
-		if v == "-s" {
+		switch {
+		case v == "-s":
 			removeDisallowed([]rune(symbols))
-		} else if strings.HasPrefix(v, "-r=") { // If argument starts with -r=
+		case strings.HasPrefix(v, "-r="):
 			// Remove all characters after the = until next whitespace
 			removeDisallowed([]rune(v[2:]))
-		} else {
+		default:
 			return "Invalid argument (\"" + v + "\") supplied! (Type gopass -h for help)"
 		}
 	}
@@ -61,28 +68,88 @@ func matchArguments(args []string) string {
 
 // Remove all disallowed characters from the allowedCharacters slice
 func removeDisallowed(disallowed []rune) {
+	disallowedMap := make(map[rune]bool, len(disallowed))
 	for _, r := range disallowed {
-		for i, v := range allowedCharacters {
-			if v == r {
-				allowedCharacters = append(allowedCharacters[:i], allowedCharacters[i+1:]...)
-			}
+		disallowedMap[r] = true
+	}
+
+	i := 0
+	for _, v := range allowedCharacters {
+		if !disallowedMap[v] {
+			allowedCharacters[i] = v
+			i++
 		}
 	}
+	allowedCharacters = allowedCharacters[:i]
 }
 
 func generatePassword(size int) string {
 	// Make empty array of runes with size of size
 	pass := make([]rune, size)
 
-	// Assign every slot of pass to a random allowedCharacter
-	for i := range pass {
-		// Generate a random int greater than 0 and not to exceed the length of allowedCharacters
-		index, err := rand.Int(rand.Reader, big.NewInt(int64(len(allowedCharacters))))
-		if err != nil {
-			println("Error securely generating random character!")
-			return ""
-		}
-		pass[i] = allowedCharacters[index.Int64()]
+	// Create a channel to receive chunks of the password
+	passChan := make(chan []rune)
+
+	// Determine the number of worker goroutines to use
+	numWorkers := runtime.NumCPU()
+
+	// Launch the worker goroutines
+	for range numWorkers {
+		go func() {
+			allowedLen := len(allowedCharacters)
+
+			// Calculate the rejection limit to avoid modulo bias.
+			// Any random byte value > maxByte must be discarded.
+			maxByte := 255 - (256 % allowedLen)
+
+			// Create a buffer for random bytes.
+			// We read enough bytes for the whole chunk at once (plus some extra
+			// in case of rejections) to reduce system calls.
+			randBuf := make([]byte, chunkSize*2)
+
+			for {
+				// Fill the buffer initially
+				if _, err := rand.Read(randBuf); err != nil {
+					println("Error securely generating random character chunk!")
+					return
+				}
+				bufIdx := 0
+
+				chunk := make([]rune, chunkSize)
+				for i := range chunk {
+					for {
+						// If we exhausted the buffer due to rejections, refill it
+						if bufIdx >= len(randBuf) {
+							if _, err := rand.Read(randBuf); err != nil {
+								println("Error securely generating random character chunk!")
+								return
+							}
+							bufIdx = 0
+						}
+
+						b := randBuf[bufIdx]
+						bufIdx++
+
+						// If the byte causes bias, discard and retry
+						if int(b) > maxByte {
+							continue
+						}
+
+						// Safe to map to character set
+						chunk[i] = allowedCharacters[int(b)%allowedLen]
+						break
+					}
+				}
+				// Send the chunk of the password to the main goroutine
+				passChan <- chunk
+			}
+		}()
+	}
+
+	// Collect the chunks of the password from the channel
+	for i := 0; i < size; i += chunkSize {
+		chunk := <-passChan
+		copy(pass[i:], chunk)
 	}
 
 	return string(pass)

makefile

@@ -1,5 +1,5 @@
 # The current version number of the program
-VERSION := 1.3.0
+VERSION := 1.3.5
 
 # List of OS and architecture combinations to build
 BUILD_OS_ARCH := \
@@ -24,64 +24,64 @@ all: $(BUILD_OS_ARCH)
 darwin/amd64:
 	GOOS=darwin \
 	GOARCH=amd64 \
-	go build -ldflags="-s -w" -o "gopass-darwin-amd64-$(VERSION)" main.go
+	go build -trimpath -buildvcs=false -ldflags="-s -w" -o "gopass-darwin-amd64-$(VERSION)" main.go
 
 freebsd/386:
 	GOOS=freebsd \
 	GOARCH=386 \
-	go build -ldflags="-s -w" -o "gopass-freebsd-386-$(VERSION)" main.go
+	go build -trimpath -buildvcs=false -ldflags="-s -w" -o "gopass-freebsd-386-$(VERSION)" main.go
 
 freebsd/amd64:
 	GOOS=freebsd \
 	GOARCH=amd64 \
-	go build -ldflags="-s -w" -o "gopass-freebsd-amd64-$(VERSION)" main.go
+	go build -trimpath -buildvcs=false -ldflags="-s -w" -o "gopass-freebsd-amd64-$(VERSION)" main.go
 
 freebsd/arm:
 	GOOS=freebsd \
 	GOARCH=arm \
-	go build -ldflags="-s -w" -o "gopass-freebsd-arm-$(VERSION)" main.go
+	go build -trimpath -buildvcs=false -ldflags="-s -w" -o "gopass-freebsd-arm-$(VERSION)" main.go
 
 linux/386:
 	GOOS=linux \
 	GOARCH=386 \
-	go build -ldflags="-s -w" -o "gopass-linux-386-$(VERSION)" main.go
+	go build -trimpath -buildvcs=false -ldflags="-s -w" -o "gopass-linux-386-$(VERSION)" main.go
 
 linux/amd64:
 	GOOS=linux \
 	GOARCH=amd64 \
-	go build -ldflags="-s -w" -o "gopass-linux-amd64-$(VERSION)" main.go
+	go build -trimpath -buildvcs=false -ldflags="-s -w" -o "gopass-linux-amd64-$(VERSION)" main.go
 
 linux/arm:
 	GOOS=linux \
 	GOARCH=arm \
-	go build -ldflags="-s -w" -o "gopass-linux-arm-$(VERSION)" main.go
+	go build -trimpath -buildvcs=false -ldflags="-s -w" -o "gopass-linux-arm-$(VERSION)" main.go
 
 plan9/386:
 	GOOS=plan9 \
 	GOARCH=386 \
-	go build -ldflags="-s -w" -o "gopass-plan9-386-$(VERSION)" main.go
+	go build -trimpath -buildvcs=false -ldflags="-s -w" -o "gopass-plan9-386-$(VERSION)" main.go
 
 plan9/amd64:
 	GOOS=plan9 \
 	GOARCH=amd64 \
-	go build -ldflags="-s -w" -o "gopass-plan9-amd64-$(VERSION)" main.go
+	go build -trimpath -buildvcs=false -ldflags="-s -w" -o "gopass-plan9-amd64-$(VERSION)" main.go
 
 plan9/arm:
 	GOOS=plan9 \
 	GOARCH=arm \
-	go build -ldflags="-s -w" -o "gopass-plan9-arm-$(VERSION)" main.go
+	go build -trimpath -buildvcs=false -ldflags="-s -w" -o "gopass-plan9-arm-$(VERSION)" main.go
 
 windows/386:
 	GOOS=windows \
 	GOARCH=386 \
-	go build -ldflags="-s -w" -o "gopass-windows-386-$(VERSION)" main.go
+	go build -trimpath -buildvcs=false -ldflags="-s -w" -o "gopass-windows-386-$(VERSION)" main.go
 
 windows/amd64:
 	GOOS=windows \
 	GOARCH=amd64 \
-	go build -ldflags="-s -w" -o "gopass-windows-amd64-$(VERSION)" main.go
+	go build -trimpath -buildvcs=false -ldflags="-s -w" -o "gopass-windows-amd64-$(VERSION)" main.go
 
 windows/arm:
 	GOOS=windows \
 	GOARCH=arm \
-	go build -ldflags="-s -w" -o "gopass-windows-arm-$(VERSION)" main.go
+	go build -trimpath -buildvcs=false -ldflags="-s -w" -o "gopass-windows-arm-$(VERSION)" main.go