Add StringGen() for generating cryptographically secure strings

stringy/gen.go

@@ -0,0 +1,67 @@
+package stringy
+
+import (
+	"crypto/rand"
+	"fmt"
+	"math"
+	"math/big"
+	"strings"
+)
+
+// StringGen generates a random string of a specified length and complexity.
+// Requires: complexity (minimum percentage of special characters to be returned in the generated string; set to 0 to generate a simple string),
+// complexCharsetLevel (1 = safe for filenames, 2 = safe for most password entries, 3 = safe only for well-made password entries)
+func StringGen(length int, complexity float64, complexCharsetLevel uint8) string {
+	var actualSpecialChars int // track the number of special characters in the generated string
+	var minSpecialChars int    // track the minimum number of special characters to accept
+	var extendedCharset string // additions to character set used for complex strings
+
+	charset := "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789" // default character set used for all strings
+	const extendedCharsetFiles = "!#$%&+,-.;=@_~^()[]{}`'"                      // additional special characters for complex strings (safe in file names)
+	const extendedCharsetMostPassword = "*:><?|"                                // additional special characters for complex strings (NOT safe in file names)
+	const extendedCharsetSpecialPassword = "\"/\\"                              // additional special characters for complex strings (NOT safe in file names)
+
+	if complexity > 0 {
+		minSpecialChars = int(math.Round(float64(length) * complexity)) // determine minimum number of special characters to accept
+		switch complexCharsetLevel {
+		case 1:
+			extendedCharset = extendedCharsetFiles
+		case 2:
+			extendedCharset = extendedCharsetMostPassword + extendedCharsetFiles[:len(extendedCharsetFiles)-9]
+		case 3:
+			extendedCharset = extendedCharsetFiles + extendedCharsetMostPassword + extendedCharsetSpecialPassword
+		}
+		charset += extendedCharset
+	}
+
+	// loop until a string of the desired complexity is generated
+	for {
+		// generate a random string
+		result := make([]byte, length)
+		for i := range result {
+			val, _ := rand.Int(rand.Reader, big.NewInt(int64(len(charset))))
+			result[i] = charset[val.Int64()]
+		}
+
+		// return early if the string is not complex
+		if complexity <= 0 {
+			return string(result)
+		}
+
+		// count the number of special characters in the generated string
+		for _, char := range string(result) {
+			if strings.ContainsRune(extendedCharset, char) {
+				actualSpecialChars++
+			}
+		}
+
+		// return the generated string if it contains enough special characters
+		if actualSpecialChars >= minSpecialChars {
+			return string(result)
+		}
+
+		// reset special character counter
+		fmt.Println("Regenerating string until desired complexity is achieved...")
+		actualSpecialChars = 0
+	}
+}