diff --git a/main.go b/main.go
index 2bb1cd6..14e2420 100644
--- a/main.go
+++ b/main.go
@@ -1,24 +1,42 @@
 package main // import "moul.io/cryptoguess"
 
 import (
-	"bufio"
+	"flag"
 	"fmt"
-	"io"
+	"io/ioutil"
+	"log"
 	"os"
 
 	"moul.io/cryptoguess/cryptoguess"
 )
 
 func main() {
-	in := bufio.NewReader(os.Stdin)
-	input := []byte{}
-	for {
-		chunk, err := in.ReadByte()
-		if err == io.EOF {
-			break
+	if err := guess(); err != nil {
+		log.Printf("Error: %v", err)
+		os.Exit(1)
+	}
+}
+
+func guess() error {
+	flag.Parse()
+	var data []byte
+	var err error
+	switch flag.NArg() {
+	case 0:
+		data, err = ioutil.ReadAll(os.Stdin)
+		if err != nil {
+			return err
 		}
-		input = append(input, chunk)
+	case 1:
+		data, err = ioutil.ReadFile(flag.Arg(0))
+		if err != nil {
+			return err
+		}
+	default:
+		return fmt.Errorf("input must be from stdin or file")
 	}
-	question := cryptoguess.New(input)
+
+	question := cryptoguess.New(data)
 	fmt.Println(question)
+	return nil
 }
diff --git a/test/pem-rsa-pubkey.txt b/test/pem-rsa-pubkey.txt
new file mode 100644
index 0000000..437dc95
--- /dev/null
+++ b/test/pem-rsa-pubkey.txt
@@ -0,0 +1,14 @@
+-----BEGIN PUBLIC KEY-----
+MIICIjANBgkqhkiG9w0BAQEFAAOCAg8AMIICCgKCAgEAlRuRnThUjU8/prwYxbty
+WPT9pURI3lbsKMiB6Fn/VHOKE13p4D8xgOCADpdRagdT6n4etr9atzDKUSvpMtR3
+CP5noNc97WiNCggBjVWhs7szEe8ugyqF23XwpHQ6uV1LKH50m92MbOWfCtjU9p/x
+qhNpQQ1AZhqNy5Gevap5k8XzRmjSldNAFZMY7Yv3Gi+nyCwGwpVtBUwhuLzgNFK/
+yDtw2WcWmUU7NuC8Q6MWvPebxVtCfVp/iQU6q60yyt6aGOBkhAX0LpKAEhKidixY
+nP9PNVBvxgu3XZ4P36gZV6+ummKdBVnc3NqwBLu5+CcdRdusmHPHd5pHf4/38Z3/
+6qU2a/fPvWzceVTEgZ47QjFMTCTmCwNt29cvi7zZeQzjtwQgn4ipN9NibRH/Ax/q
+TbIzHfrJ1xa2RteWSdFjwtxi9C20HUkjXSeI4YlzQMH0fPX6KCE7aVePTOnB69I/
+a9/q96DiXZajwlpq3wFctrs1oXqBp5DVrCIj8hU2wNgB7LtQ1mCtsYz//heai0K9
+PhE4X6hiE0YmeAZjR0uHl8M/5aW9xCoJ72+12kKpWAa0SFRWLy6FejNYCYpkupVJ
+yecLk/4L1W0l6jQQZnWErXZYe0PNFcmwGXy1Rep83kfBRNKRy5tvocalLlwXLdUk
+AIU+2GKjyT3iMuzZxxFxPFMCAwEAAQ==
+-----END PUBLIC KEY-----