diff --git a/cmd/taler-auditor-offline-signing/main.go b/cmd/taler-auditor-offline-signing/main.go
index d35bc18..78e2809 100644
--- a/cmd/taler-auditor-offline-signing/main.go
+++ b/cmd/taler-auditor-offline-signing/main.go
@@ -608,14 +608,24 @@ func Sign(input *Input, url string, pk ed25519.PrivateKey) ([]SignOperation, err
 }
 
 var (
+	injson  = flag.String("input", "-", "input json for signing")
 	keyfile = flag.String("key", "auditor.key", "filename of EC25519 private key")
 	url     = flag.String("url", "https://auditor.codeblau.de/", "auditor url")
 )
 
 func main() {
 
+	flag.Usage = func() {
+		fmt.Fprintf(flag.CommandLine.Output(), "Usage of %s:\n	%s [Options] (show|sign)\nOptions:\n", os.Args[0], os.Args[0])
+		flag.PrintDefaults()
+	}
 	flag.Parse()
 
+	if len(flag.Args()) == 0 {
+		flag.Usage()
+		os.Exit(1)
+	}
+
 	if len(*keyfile) == 0 {
 		log.Println("keyfile needed")
 		return
@@ -626,25 +636,48 @@ func main() {
 		log.Printf("couldn't read keyfile: %v\n", e)
 		return
 	}
+
 	pk := ed25519.NewKeyFromSeed(k)
+	pub := (pk.Public()).(ed25519.PublicKey)
+	pe, _ := crockfordEncode(pub)
 
-	input := new(Input)
-	dec := json.NewDecoder(os.Stdin)
-	e = dec.Decode(input)
-	if e != nil {
-		log.Fatal(e)
-	}
+	switch flag.Arg(0) {
+	case "show":
+		fmt.Printf("public key: %s\n", string(pe))
+	case "sign":
+		var dec *json.Decoder
 
-	output, err := Sign(input, *url, pk)
-	if err != nil {
-		log.Fatalf("error signing: %v", err)
-	}
+		input := new(Input)
+		if *injson == "-" {
+			dec = json.NewDecoder(os.Stdin)
+		} else {
+			f, e := os.Open(*injson)
+			if e != nil {
+				log.Fatal(e)
+			}
+			defer f.Close()
 
-	enc := json.NewEncoder(os.Stdout)
-	enc.SetIndent("", "  ")
-	e = enc.Encode(output)
-	if e != nil {
-		log.Fatal(e)
+			dec = json.NewDecoder(f)
+		}
+		e = dec.Decode(input)
+		if e != nil {
+			log.Fatal(e)
+		}
+
+		output, err := Sign(input, *url, pk)
+		if err != nil {
+			log.Fatalf("error signing: %v", err)
+		}
+
+		enc := json.NewEncoder(os.Stdout)
+		enc.SetIndent("", "  ")
+		e = enc.Encode(output)
+		if e != nil {
+			log.Fatal(e)
+		}
+	default:
+		flag.Usage()
+		os.Exit(2)
 	}
 
 }