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96 lines
2.5 KiB
96 lines
2.5 KiB
package main
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import (
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"bufio"
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"flag"
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"fmt"
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"io"
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"os"
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"strconv"
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"strings"
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"unicode"
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)
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// Function to decode number pairs into characters
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func decodePair(pair string) rune {
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alphabet := " ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
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num, err := strconv.Atoi(pair)
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if err != nil || num < 0 || num >= len(alphabet) {
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return rune(-1) // Return -1 if pair is not valid
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}
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return rune(alphabet[num])
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}
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// Function to apply the reverse shift and wrap around
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func applyReverseShift(value, shift int) int {
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shifted := (value - shift) % 37
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if shifted < 0 {
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shifted += 37
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}
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return shifted
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}
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func main() {
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// Define command-line flags
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shift := flag.Int("s", 0, "Shift amount for the cipher")
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flag.Usage = func() {
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fmt.Fprintf(os.Stderr, "Usage: %s [options] <<< \"String\"\n", os.Args[0])
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fmt.Fprintf(os.Stderr, " %s [options] < file.txt\n", os.Args[0])
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fmt.Fprintf(os.Stderr, " echo \"string\" | %s [options]\n", os.Args[0])
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fmt.Fprintf(os.Stderr, "\nDescription:\n")
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fmt.Fprintf(os.Stderr, " A companion program to numberstation, intended to make easy work of decrypting very basic ciphers for numbers station projects using the logic of nsencode.\n")
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fmt.Fprintf(os.Stderr, "\nOptions:\n")
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flag.PrintDefaults() // Print the default flag help information
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fmt.Fprintf(os.Stderr, "\nExamples:\n")
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fmt.Fprintf(os.Stderr, " %s -s 2 <<< \"22101 12102 11210 20302 22072 122\"\n", os.Args[0])
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fmt.Fprintf(os.Stderr, " %s -s 16 < file.txt\n", os.Args[0])
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}
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flag.Parse()
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// Check if there is input from stdin
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info, _ := os.Stdin.Stat()
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if (info.Mode() & os.ModeCharDevice) != 0 {
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flag.Usage()
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os.Exit(1)
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}
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// Read all input from stdin
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reader := bufio.NewReader(os.Stdin)
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inputBytes, _ := io.ReadAll(reader)
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input := string(inputBytes)
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// Remove all spaces and line breaks
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input = strings.ReplaceAll(input, " ", "")
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input = strings.ReplaceAll(input, "\n", "")
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input = strings.TrimSpace(input)
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var decoded strings.Builder
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// Decode the input string
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for i := 0; i < len(input); i += 2 {
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if i+1 >= len(input) {
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break // If there's an odd number of characters, break out
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}
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pair := input[i : i+2]
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num, err := strconv.Atoi(pair)
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if err != nil {
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continue // Skip invalid pairs
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}
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shiftedValue := applyReverseShift(num, *shift)
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char := decodePair(fmt.Sprintf("%02d", shiftedValue))
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if !unicode.IsPrint(char) || char == rune(-1) {
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continue // Skip invalid characters
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}
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decoded.WriteRune(char)
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}
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// Output the decoded string
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fmt.Println(decoded.String())
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}
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